Are You Interested in Propagating Rhododendrons or Azaleas from Cuttings?
The following articles describe many different methods. Some of these are for large scale efforts, and some are for kitchen table hobbyists. Some presentations address only rooting the cutting; while others also detail the after care. Anyone interested in growing rhododendrons and azaleas from cuttings should be able to find a method and/or technique among the following ideas to fit his or her individual needs.
Propagation Of Rhododendrons By Cuttings
Pete McNees, Tuscumbia, AL
Art - the ability to make or do things through the skill of an artist.
Science - knowledge made up of an orderly system of facts that have been learned from study, observation and experiments.
The practice of rooting plants in the Genus Rhododendron is a changing and hopefully never ending procedure. As information is disseminated to those who are interested, the ability to root cuttings gets nearer to a science and less of an art. In the early days of developing the methods used there were established guilds. These people guarded their hard won information and it was passed within the guild members and these were mainly within the confines of the family unit. In the early days secrecy was the order. There are many of the older hybrids where the parentage is unknown because of this secrecy. Today through various publications, books, periodicals, and societies, this information flows in a never ending stream of words. Today I believe there is in the propagation of rhododendrons a tilting toward the science of propagation and less of an art. There is still the art of feeling the cuttings, the timing, seeing to their proper care and to be in communion with the plants. These things will ever be. But there is now available an outline that can be prepared. By searching out the steps to be followed the chances of success are extremely high.
There is both a feeling of joy and sense of sadness as this happens. The great joy is being able to root cuttings with some success in an initial effort by doing exactly what is required. If you add 2 + 2 + 2 you will get 6 every time as this is one of the laws of mathematics and by following the propagation laws you will get rooted cuttings every time.
Well now to these laws of propagation. It is my hypothesis that someone who has never done anything but cut grass, can by following exactly this outline; get ten rooted cuttings of rhododendrons out of twenty cuttings attempted. Commercial nurseries can and do survive on a percentage of 50% success. I have no doubts that you can do that well or better the first time you try.
Big Boss Pepsi bottles
Styrofoam cups (about 12 oz. size)
Rooting Hormone 2% indolebutyric acid with 5% Benlate in talc. (from local druggist)
One gallon size freezer bags with ties
Strainer type used for french fries
Marking pen (permanent ink)
Three gallon container
One gallon bucket
Timing - early in the morning preferably after a rain the night before. Here in North Alabama anytime after the first of July when the cutting is no longer sticky to the touch.
Type Cutting - take the cuttings from the side of the plant where there are at least three new shoots growing from one terminal. If there are at least three take one and if as many as five you can take two. Do not take more than 20% of the cuttings available on any one plant and if this is done annually the fourth year the plant must be allowed to rest one full year.
Taking the Cuttings - with a very sharp knife cut the stem close to the base at the next whorl of leaves, whereby you get the longest cutting you can. It can be shortened later and your plant will look better if there is no long stem sticking up without any leaves.
Rooting Mixture - take a measured amount of peat moss probably one gallon and screen through a strainer into a container that will hold at least three gallons. Add water to the peat moss until there is enough to thoroughly wet the mixture. Next take your hands and squeeze the peat moss in the water until it is completely wet. Take the wet peat moss and squeeze most of the water out and put it back into the gallon container. Clean your three gallon container and screen the wet peat moss back into the three gallon container and add an equal measure of perlite which in the above case would be one gallon. With your hands thoroughly mix the two ingredients until you have a light and fluffy rooting medium.
Holding - If there is to be any delay in the sticking of the cutting take one of the freezer bags and put some water in the bag then shake out all the water and what is left in the bag will be enough to keep the cutting fresh. Put the cutting in the bag along with a label for later identification and blow up the bag like a balloon. Twist the top of the bag to retain the air inside and seal with a tie.
Dip - the following is to be used as a dip for the cuttings. (Stirred prior to each variety)
2 gallons water
1 tablespoon Benlate
1 tablespoon Malathion
Put cuttings in dip before working up.
Cutting Preparation - Reduce the leaves of the cutting to 4 to 6 each. Each leaf of the cutting is reduced in size by 1/3 to 1/2 depending on the size of the leaf. The length of the cutting is reduced in size to about three inches. Each cutting is then double wounded (meaning a slice of the cutting at the base is cut off about the bottom inch of the cutting on two sides). This wound should be just through the cambium layer and is not cut too deep into the wood of the stem.
Container - the Styrofoam cups are notched along the bottom where the sides join about 4 times around the cup. This gives drainage. These cups are then filled to overflowing with the rooting mixture and tapped on the bottom about three or four times to settle the mixture. Do Not Pack
Inserting & Hormone Dip - Take the unsharpened pencil and punch a hole in the center of the rooting mixture to receive the cutting. This hole should be about two inches deep. The cutting should be somewhat dryer after the dip and you have worked it up. Dip the cutting in the 2% indolebutyric acid about one and one half inches (cover completely the double wound). After the dip tap off the excess hormone and stick the cutting in the hole in the container. Gently (repeat gently) firm the rooting mixture around the cutting.
Watering - with the watering can completely wet the cutting and the mixture until there is water flowing out the bottom of the holes in the cup. Water from at least two sides of the cup. By using a watering can oxygen will be added to the mixture which is necessary for rooting.
Pepsi-Bottles - Set the cup in the black base of the Pepsi bottle and place the clear cover over and around the cutting. Press down until the top goes down about an inch or less.
Labels - At all times the label with the identification of the plant must be kept with the cutting and it can be inserted in the medium facing out for you to see during the rooting period.
Location During Rooting - The cuttings are now ready to be put in the shade for the time necessary for rooting. All direct (repeat all direct) sunlight must be eliminated. On the north side of your house would be a good place to set the bottles. They need all the light that is available: but again no direct sunlight as they will cook in a very short time if it ever reaches them.
The plants are left in the bottles undisturbed for 12 weeks. Then the top of the container is raised and left off for one hour late in the afternoon for three days. At this time additional water from the watering can is added. The container is then removed at night for three nights and then removed altogether. The plants are left in the same place where they rooted during this period. If you and I have been in communion through the above during the period of rooting and I have told you all to do and you have done everything above - you will have at least fifty percent of the plants you inserted with roots - be very careful with these at this time as they are not firmly attached and are easily broken off. Pot these plants up in one gallon pots with a mixture of one third peat moss, one third mini nugget pine bark and one third good top soil. Keep them watered and protected during the winter and they will be ready for planting in your yard early in the spring.
Remember there are no short cuts. All of these that I have tried have in the end cost me in the success percentage. Have fun and it really does work.
Marie Tietjens, Blue Bell, PA
Max and I are not professionals. We are strictly avid hobbyists. We grew up in New York City. Our first garden was a window box outside our fifth story apartment. We spent many hours in the Bronx Botanical Garden admiring the plants. I recall writing down the name of one plant we just loved. It was a rhododendron.
During the war when we lived in New Jersey, we had a victory garden. Our interest in exotic gardening did not materialize until our children were grown, married and gone. We got rid of the sandbox and swings and started our garden.
We owe thanks to two, in our estimation, very great men in Rhododendron circles who are no longer with us. One was Jim Sholomskas and the other was John Schamenek. It was Jim who invited us to a meeting of the Philadelphia Chapter of the American Rhododendron Society. Jim was president at that time. Max, who was a building inspector and zoning officer for the township, went to Jim's house to inspect a picture window Jim put in facing his beautiful garden. Max was awed by the beauty. Jim gave him some literature which we read before we went to the meeting. Shortly afterwards, Jim asked me if I would help him out by being temporary secretary for four months. The secretary at the time wanted to resign. In spite of the fact that I was totally green, I said "yes." Well, the four months lasted five years. In addition to being secretary, I was also given the "honor" of being elected treasurer too. I held both positions at the same time for five years. No regrets. I learned a great deal.
We had invited John Schamenek to a picnic at our home. We were very proud of our border plantings. John took one look at our grounds and told Max, "Max, you've got too much lawn." Well, that started it. Max dug into the lawn, starting at the right hand corner of our property. Among the rhododendrons and companion plants he put in was a plant John had given us and which he thought very highly of. It was a rhododendron he had hybridized: R. smirnowii x R. yakushimanum - very heavily indumented foliage, excellent plant habit and beautiful apple blossom pink and white flowers. In John's memory, after he passed away, we had this plant registered as 'Schamenek's Glow'.
When Lloyd Partain and Charlie Herbert came to take pictures of this plant and fill out the necessary papers, Lloyd saw another rhododendron in bloom that he thought worthy of being registered. It was a plant I started from seed, a cross of 'Goldfort' x 'Full Moon' which was registered as 'Goldmoon', a beautiful large white flower. Also registered at this time was another rhododendron I started from seed, a cross of Gable's Vernicosum 18139 #1 x 'Full Moon,' which I named 'Marie Tietjens'. The multicolor flowers of peach, pink, yellow and white, were absolutely gorgeous. I must admit I have been very disappointed in the plant habit since then.
When the Philadelphia Chapter ARS exhibited for the first time at the flower show, Max helped set up the exhibit. It was the first time he had ever been to the Philadelphia Flower Show. He was so inspired by what he saw. He came home bubbling with enthusiasm. He said he was going to build a mountain, a stream, a pond, a waterfall and a bridge. I let it go in one ear and out the other. The next day when I came home from work, there was a load of rock and dirt in the middle of our lawn. "0h, no," I thought, "he's really flipped his lid this time." "What will the neighbors think?" Well, he began to create and what he visualized became a beautiful reality. This was a continuation of the first garden he created. Each year thereafter, Max would dig further into the lawn creating new gardens, each one different. I wondered about some of his radical ideas, but he has the ability to visualize and the end results were always artistic and beautiful. We have utilized all the space we have and we have even encroached on our neighbor's property, with their permission, of course. In addition to our rhododendrons and azaleas, we have companion plants, bulbs, a scree, rock garden plants, wild flowers, roses, dwarf conifers, heather, cacti, etc. Max has also incorporated artistically many mineral specimens, interesting tree stumps and driftwood. While Max is the landscape artist and gardener, I am the propagator. This is my love.
What is my method? It is a very simple, efficient and rewarding method of propagating cuttings outdoors under glass jars. I use no bottom heat, no misting, no strong hormodin powders. I let mother nature do most of my work for me. It is ironic that the very primitive method and the very latest, sophisticated tissue culture method, both use glass jars.
What, when, where and how do I propagate?
WHAT? Anything and everything; azaleas, rhododendrons, dwarf conifers, trees, roses, Chrysanthemums, rock garden plants, etc.
WHEN? Whenever the opportunity presents itself; from January 1st to December 31st. I recall one instance while touring the Wister's garden in Swarthmore, I asked Dr. Wister if I might have a cutting of R. mucronulatum 'Cornell Pink', which I always admired. "But Marie," he replied, "is it the right time?" I gave him my stock answer, "Dr. John, when the opportunity presents itself, that is the right time for me." With that, he told me to help myself. So, in the pouring rain, I did just that. The cutting took and grew into nice healthy plants. I have since taken cuttings of the cuttings and have spread the cheer around. My greatest delight is in giving away plants that I have propagated. I have, perhaps, been influenced by a remark Line Foster made at one of the Rock Garden Society conventions when Max and I were comparatively new members. He told us the importance of sharing plants; of extending beauty. When you share a plant, you never lose it. You can always get a cutting back if you lose your own plant. I am a firm believer in sharing and in spreading beauty. Besides, I have a mania for propagating plants. I must propagate anything and everything - especially when someone says it can't be done. My daughter-in-law has spread the rumor that I can propagate a broomstick.
WHERE? My original propagating bed, which I still use, is a protected area about 4 'x 4', in front of our house, facing north. This is actually a natural Nearing Frame. The cuttings are protected by the wall of the house. Some azalea bushes in front of the propagating bed not only protects the plants too, but hides the view of the unsightly jars. The area gets light but no direct sun, which is very important. I can strike about 100 cuttings here. At first, I did nothing to the soil, which was the worst imaginable foundation excavation soil. Would you believe that I had tremendous luck with my cuttings? Max has since added quite a bit of peat moss, sand and humus and has made the soil loose and friable.
I have encroached on another area; a raised bed alongside the fence of our pool, facing north. We had azaleas here at one time, but they did not do too well on account of the shade from the apple tree nearby. As Max moved the azaleas, I took over with my jars, much to Max's disgust and horror. He is such a perfectionist that the thought of seeing all those exposed jars, all sizes and shapes, just did not appeal to him at all. He called it the "city dump." Elaine Kern, a friend of mine called it the "crystal" garden. I like that name much better. Recently, someone called it a "bubble" garden. Someone else refers to me as the lady with a thousand green houses. So, what's in a name?
HOW? I take a cutting, preferable one without a flower bud, just below a leaf node. The size of the cutting is dependent upon the size of the plant. If it is a dwarf rhododendron or a dwarf conifer, I usually take about a 2" cutting. If it is a medium leaf rhododendron, I would take about a 3" to 4" cutting. If it is a large leaf rhododendron or a dogwood or a cut leaf maple, I would take about a 6" cutting. If the leaves are large, I cut the leaves in half. I remove some of the lower leaves. At either end of the base, I shave off a sliver about 1" long for a large leaf rhododendron and much less, if anything at all, on the smaller plants. As I said earlier, I do not believe in strong hormodin powders. If I use anything at all, it is some old rootone that someone had given me years ago and which has probably lost all of its effectiveness. I then put the cutting right into the ground and put a jar over top. Mother nature takes over at this point, I do not water unless we have a particularly dry spell in the summer. Patience is a virtue at this time. I am not in any particular hurry to remove the jars. From time to time, I would lift up the jars to see how the plants are doing. I am a firm believer in the "power of positive thinking". I know in my mind that the cutting is going to take - and it usually does. If, for some reason, it doesn't, I remove it, stir up the soil a bit and put another cutting in its place. When do I remove the jars? Well, that depends. Instinct guides me. Usually, after sufficient growth has been made. Sometimes it takes a year and sometimes it takes two years. When the plant has made sufficient growth after the jars have been removed, it can then be moved into a nursery bed for further growth, or somewhere in the garden, or it can be given to someone who might appreciate it. Since these plants have been exposed to the elements, they will not suffer from transplanting. They are good, healthy, strong plants that should continue to grow well with the proper care.
I want to give you a quick lesson in propagator's math. If you strike ten cuttings and only one takes, that's 100% success. Why? It's one more plant than you had before so that makes it 100%. If two plants take, it's 200% success and so on.
A Grafting Technique which Encourages Own-Rooting of Scions
Jack Ayers, Oakton, Virginia
Any propagator who has been discouraged by advice that a particularly desirable plant is "difficult" or "impossible" to root realizes the value of grafting techniques. Many of us are, however, hesitant to resort to grafting either because it appears to be more difficult than rooting cuttings or because we have read the often published advice that grafted rhododendrons are not as vigorous or healthy as own-rooted plants. In an article on rhododendron propagation, Ross Davis (1) described a solution to the latter problem. He suggested that hard to root clones be cleft grafted near the base of an easy to root cutting and that the union be buried when potting the rooted cutting so as to encourage root formation from the scion. His description prompted me to speculate that own-rooting might be even more likely if the difficult and easy to root cuttings were side grafted and struck to an equal depth in the rooting medium. My initial experiments with this technique were successful enough to encourage me to compose this short article in order to recommend it to others for trial. When Ed Egan received my manuscript he recognized the technique as one used for over twenty years by Cy Ward, the most widely known propagator in the Portland area. Cy relates that the technique is of ancient Chinese origin and that he read about it and adopted it to modern materials and methods. Cy calls the technique "Scion on Scion" rooting. His long experience with the method further encourages me to recommend it to readers of the Journal.
I have conducted tests by grafting the desired cutting to similar size cuttings of 'County of York,' a clone which roots very easily. For rooting difficult varieties of small stature one might prefer grafting to a cutting from an easily propagated plant of smaller size. Both cuttings are prepared exactly as described by Leach (2) for the rooting of stem cuttings. This preparation consists of trimming off excess leaves and of wounding the stem by slicing through the bark and cambium layer of the bottom 1 inches, on both sides. Remove all axial buds on the lower portion of the less desirable cutting so as to preclude sucker formation. Place the two cuttings side-by-side with their bases even and their cambium layers matched, and join them with a rubber band which is stretched just enough to prevent a relative motion of the two cuttings during subsequent handling. The joined cuttings are now handled exactly as is any normal cutting, except that all growth buds are broken out of the undesired cutting as they swell.
In mid July of 1984 I prepared the joined cutting pair, another joined pair of the same varieties, and a pair consisting of 'Spellbinder' and 'County of York.' All three were dipped in a Benomyl solution, soaked for 16 hours in a 75 ppm solution of indole-3-butyric acid, and struck in a moist mixture of 2/3 sphagnum, 1/3 perlite. The cuttings were maintained under lights in a basement with temperatures ranging from 75 degrees in August down to 60 degrees in mid-winter. By mid August the 'Spellbinder' cutting was dead from an unidentified fungus infection, but its 'County of York' mate proceeded to root and make rapid growth. Both 'Hardy Giant'/'County of York' pairs were well rooted within 12 weeks. When the pair with more rapid root growth was potted on Nov. 24, its root mass was found to completely fill the 2 inch deep potting medium within the one-gallon milk jug bottom in which it was stuck. 'Hardy Giant' is reported to be a difficult plant to root and is still very rare even though it is a sought after plant which was hybridized in 1952. Because of its rarity I did not disturb either root ball to determine what fraction of the roots, if any, originated on the 'Hardy Giant' stem.
Bud swelling was evident on the 'Hardy Giant' of the more advanced pair by the end of November, and on the second by the end of December. On both plants this first growth cycle yielded a growth stem of only 1 inches, but several leaves exceeded 8 inches in length. Both plants are beginning a second growth cycle at the time of this writing in early February of 1985, and I look forward to seeing soon some of the truly magnificent leaves for which this plant is noted (perhaps the largest on any rhododendron dependably hardy in the East).
As was mentioned above, all growth buds on the less desirable mate should be removed as they swell, but no further action is required. This portion of the united plant will die in time and the desired portion will proceed to grow just as it would if one of its weaker branches failed. You need not worry about the rubber band either, for it will disintegrate with time. I find this method to require no special skill and estimate that it should add no more than 20 minutes total, per plant, to the time one normally invests in starting a new plant from a cutting. I believe you might find that small investment will yield a large return.
I am grateful to Ed Egan for familiarizing me with Cy Ward's use of this technique, and for publishing my description, despite the fact that others have long known the value of the method.
1. Davis, Ross B., Jr., (1980), Quarterly Bulletin, American Rhododendron Society, 34, 3, pp 160-162.
2. Leach, David G., (1960), Rhododendrons of the World, Charles Scribner's Sons, New York, p 317.
Rhododendron And Azalea Propagation Methods
Emil V. Bohnel, Pearl River, NY
- Cut leaves 1/3 off if too long. Cuttings, taken the day after the plant has been thoroughly watered, from the north side of the plant, should be cut 2" long. Thin stemmed rather than thick or stout stemmed cuttings are best.
- Wound cuttings: Cut the cambium layer of the cutting with a sharp knife or razor blade down to the wood on two sides opposite each other. One side 1 ", the other side ". Do not slice to the end of the cutting but begin wound about " from the end of the cutting. Immerse cuttings in a solution of fungicide Benomyl (1 tablespoon per 2 gals, water).
- Prepare solution of either regular ROOTONE or #10 ROOTONE (for professional use). Moisten ROOTONE with 95% ethyl alcohol. 'Vodka' may be substituted. ⅛of a teaspoon alcohol moistened ROOTONE stirred into 1 gallon of rainwater or distilled water. Allow the cuttings to soak in the ROOTONE solution for 18 hours. Put stems through holes in cover of plastic container filled with ROOTONE solution.
Strike the cuttings in either:
a. Nearing Frame
b. Plastic covered flat
- The frame or flat should be situated in an area devoid of sun. An exposure should be found where only reflected northern light obtains. No sunlight should be available to the cuttings. It has since been found that a Nearing frame roof of frosted fiberglass affords the cuttings more light and encourages the rooting of the cuttings better than the reflected northern light of a Nearing frame with a tin or aluminum roof. A glass frame should cover the cuttings either way. Both frames work in encouraging rooting of cuttings.
- MEDIA: Equal volumes of peat moss plus PERLITE. Thoroughly washed coarse builders sand may be substituted for PERLITE. If sand is used, clay must not be present - wash it out thoroughly.
- Cuttings may be taken either in July or October, only when thoroughly hardened off. Cuttings are hardened off when they are not sticky, are smooth and dry on the stem surface. Trial and error is the only way the best time to take cuttings will be found. Some cuttings would not root for me when taken in October but would root when the cuttings were taken in July. The use of bottom heat eliminates this problem. This bottom heat propagator makes it possible to root the most difficult cuttings if taken when they are hardened off.
- After the cuttings have been struck, they should be watered in and kept moist at all times. Cuttings should be set apart so that the leaves will not touch each other. Condensation on the surface of the glass or plastic cover will show that sufficient moisture is present. Water the cuttings when condensation is not present or when the media appears dry.
- I have found that 4" clay pots or yogurt cups with holes punched into the bottom for drainage sunk to the rim in frame or flat to be the most efficient method in rooting cuttings when the following media is used: Moderately composted PINE NEEDLES placed 1/3 in the bottom of the pot. The pot is then filled with 2/3 peat moss plus PERLITE or sand. It is my contention that by using composted pine needles, mycorrhizae are present and these fungi promote the rooting of rhododendron and azalea cuttings.
- The above method makes it possible to tap out the media from the pot to see if the cutting has rooted. If the cutting has not rooted, it can be replaced into the pot and placed back into its place in the frame. If cuttings are placed directly into the media in the frame, in order to know whether they are rooted they must be dug out. This method of digging up the cutting can create a mess in the frame and disturb the other cuttings.
- Another plus is that the entire media in the frame will not have to be replaced each year. Only the media in the pot requires changing when the rooted cuttings are removed. The un-rooted cutting may be replaced into its pot and be placed back into the place in the frame.
- I water the cuttings twice weekly in the summer whether they require it or not since when you water, oxygen is flushed to the root area in this manner. Never water when the media in the frame is frozen. It is best to give a thorough watering just before you expect a freeze, before the cuttings go into the winter season.
- Plants should be thoroughly watered the day before cuttings are taken. Only cuttings with leaf buds should be taken. When lepidote, small leaved cuttings are taken it is sometimes difficult to find cuttings without flower buds. Remove the flower buds in this situation.
- Lepidote and azalea cuttings need not be wounded.
- Cuttings should be struck at an angle of about 60 degrees in the media.
- When cuttings are found to be rooted they should be transplanted into a growing media and kept in a moderately shaded area. A lath house or a frame allowing 50% sunlight is the best condition for growing rooted cuttings.
- A covered frame is best for wintering newly rooted cuttings.
- I have had the most success in taking azalea cuttings in July, when they are springy, not stiff and striking them in thoroughly washed sand.
- Azalea cuttings should be bent at the tip of the cutting and severed at the spot where the cutting remains firm. Discard the tip of the cutting.
- Three to four leaves are left to remain on elepidotes, (large leaf cuttings). Six to seven leaves are left on azaleas, four to five leaves are left on lepidotes, (small scaly leafed cuttings).
- I have found that tip cuttings of newly grown seedlings root in about two months under fluorescent lights and make sturdier plants than the original seedlings left to grow on their own.
- MEDIA: 50% peat moss plus PERLITE plus a small amount of charcoal is the media used for tip cuttings.
- In order to obtain a well branched plant from a rooted cutting, the leaf bud at the tip of the branch on the new growth should be pinched. A sturdy well branched plant will result.
Aluminum Beer Can Labels:
a. Cut the label to the size to fit the name. Place several layers of newspaper on the surface picked to work. With a sturdy ball point pen, print the name by putting a little pressure with pen on the aluminum label.
b. Use a Dymo labeler. Place the printed name into two slits cut in each end of the label. Fit the label and close the slits with a pair of pliers.
How To Grow Rhododendron Seedlings And To Root Cuttings
Russell Gilkey, Kingsport, TN
There are as many methods for growing rhododendron seedlings as there are people who grow seedlings. This is another procedure to add to the list of those already published in the Journal of the American Rhododendron Society and elsewhere. The advantage of this method, as I see it, is that you can grow as few or as many seedlings as you wish to a fair size inside your house, with a minimum of care. One disadvantage is that it is sometimes hard to find the containers (plastic boxes) which I'm going to recommend. Other disadvantages will be mentioned in due course. I'm sure you will be able to eliminate those which affect you by modifying the procedure for your own use. If you want to grow only a dozen or less plants, you can. On the other hand, you can grow thirty dozen or more if you set up shelving of suitable dimensions to accommodate the boxes, and outfit each shelf with fluorescent lighting.
Rhododendron seed that you get from the ARS Seed Exchange or from other sources will have varying histories. Some seed capsules are collected early in the fall; some late. Some are ripened on the plant; some are collected green and then dried in various ways, such as indoors at room temperature, or in a refrigerator, or over chemical drying agents. Some seeds, yakushimanum for instance, require a cold period to break dormancy. The germination percentage will therefore vary, not only due to the percentage of the seed, but also to the conditions during development and subsequent processing of the seed capsule and the seed. Most seed (40%-80%) will germinate well in the condition in which they are received. A few won't germinate, period. Some, of course, will be intermediate. If you want to play it safe, just in case the seeds need a cold period to break dormancy, sow them and then store the box in the refrigerator at 35°-40° F. for 4-6 weeks before placing the box under fluorescent light at 65°-75° F. for germination. For example, the germination percentages for five 1984 seeds from the seed exchange, representing a range of germination percentages, were 30/22, 40/20, 67/52, 50/11 and 40/31 with (5 weeks)/without cold storage. R. yakushimanum seed, as previously mentioned, will germinate much better after a cold storage treatment. If the experiments I have planned for yakushimanum seed pan out, they might be worth reporting at some future date.
For germinating the seed I use a clear plastic shoe box with a clear plastic lid. The box is 12" x 6" x 3". The last ones I got came from Woolworth and were made by Sterilite Corp., Townsend, MA 01469. No provision is made for drainage. I usually saw or cut plastic dividers to divide the box into 2 or 3 sections. A different variety of seed is sowed in each section. The boxes are used over and over, so the first step is to wash and sterilize box and lid. Household Clorox is used for sterilization. Swish it around and give it a few minutes contact time. Rinse and dry. For planting medium for one box use (by volume) 4 cups of milled sphagnum (e.g. Mosser-Lee No damp off), 2 cups of vermiculite, and 2 cups of water in which 1/6 teaspoon of Benlate (also called Benomyl) has been dispersed. I have a spoon that came with a doll tea set (hereinafter called doll spoon) which measures 1/6 teaspoon when full and level, and this is what I use. Mix ingredients thoroughly and spread evenly in box. To compact and smooth the germination medium, press moderately with a fat object.
I generally divide the box into two sections and sow about 60 seeds in each section. The seeds are first scattered on a piece of white paper. A long fireplace matchstick moistened on one end is used to pick up one seed at a time and touch it to the germination medium surface, about " in each direction from its neighbors. After sowing seed, mist spray each section with 50 strokes (approx. oz.) of a hand-levered mister (available in discount stores) containing 2 level doll spoons Benlate in 20 oz. water. This is equivalent to 2 teaspoons per gallon, whereas the amount recommended by the manufacturer for spraying plants outdoors is 3-6 teaspoons per gallon. Put lid on box and place box 2"-3" below fluorescent light tubes, at room temperature. My room temperature in the winter is 70°F. I use cool white bulbs and time the light to turn on at 7 A.M. and off at 11 P.M. Generally the seeds will start germinating in about 2 weeks and will continue germinating over a period of about one month.
Nothing else needs to be done before transplant time, with the following exceptions. The variables associated with spores on the seed, in the medium or in the air, and with sanitation, fineness of spray, fit of box lid, temperature, heat from lights, room humidity, etc. preclude a perfect response for everyone every-time. Thus, the mention of adverse effects (which have occasionally been my lot) seems to be in order. If mold or mildew develops on seed or detritus that came with the seed, mist spray with Benlate again; maybe 10-20 mister strokes, using freshly made up suspension. Don't overdo the spraying or you'll get the medium too wet. The top of the medium should look damp but not wet or soggy. One indication of too much water is the formation of water mold or other unsavory looking growths. Amazingly enough, these don't seem to bother the seedlings too much, and the Benlate treatment keeps them in check if they occur. After the seedlings have developed a set of leaves and the roots have penetrated the medium, you can keep them growing and healthy by fertilizing every 2 weeks with a freshly made mixture of 1 level doll spoon of Benlate and 1/2 level doll spoon of Miracid (available in all lawn and garden departments) in 20 oz. of water. Give each section 10-20 strokes of mister (fine mist). If the leaf tips start turning brown you are applying too much water and/or fertilizer. You may have to crack open the box lid for a few days to let some moisture evaporate. Watering (mist spray) is indicated if the surface of the medium starts looking dry. Most of the time these measures won't be necessary, but in the well-known words of Robert Burns, "The best laid schemes o' mice an' men gang aft a-gley." Don't forget to label the box or box section with the seed number and/or the rhododendron variety. It wouldn't hurt to identify the box and its seed in a notebook as well.
In the course of 12 years of growing seedlings I have started germination of seed anywhere from Nov. 5 to May 19. Generally, my crosses were started in December and seed from the seed exchange in late March or early April. There's a disadvantage in starting them too early in that the seedlings may get too tall for the transplant boxes which are used in the next step much sooner than you wish them to. More will appear about that later.
The next step in the procedure is to transplant the seedlings to a larger container. This can be done from 7 to 16 weeks after the seed has germinated. Mainly it will depend on how tall the seedlings get, how crowded they are and/or when transplanting is convenient. My usual time is 11-12 weeks after germination. You may be able to leave them in the shoe box as much as a year if you stop fertilizing. I transplant into clear plastic sweater and storage boxes with clear plastic lids. The dimensions of these boxes are 16" x 11" x6". Unfortunately, these boxes don't seem to be readily available. I have found them at drug stores, discount stores, and Woolworth's, but not as regularly stocked items. Three companies that produce them are: Lerner Manufacturing, Inc., Melville, L.I., NY 11746; Hugh H. Wilson Co., Sunbury, PA 17801; and Sterilite Corp., Townsend, MA 01469. The Sears 1985 spring catalog has boxes of this type, but they have colored rather than clear lids and therefore are not suitable. Don't get the ones that are only 3" deep. The seedlings would be pushing up the lids before you could turn around.
Wash and sterilize the storage box and its lid as previously described for the shoe box. For one box use 12 cups of ordinary sphagnum peat, 12 cups of perlite, 6 cups of vermiculite, and 7⅔ cups of water containing 2 level doll spoons of Benlate, all well mixed together. Place the planting mix in the box and hand level. Leave it loose; don't compress it. I plant 35 seedlings in a box, using evenly spaced toothpicks, 5 across and 7 lengthwise, to plot their location. Transplanting the seedlings is easy. You need an instrument (knife, fork, stick, screwdriver or whatever) to dig around the seedling to loosen it. Then lift it out with thumb and forefinger by a leaf, transfer it to a proper size hole in the larger box, and level the medium around it. A proper size hole is one which will accommodate the root ball and place it at the same depth as it had been originally. How many seedlings should you grow further? There is no satisfactory answer. Most of us can't raise enough of a rhododendron cross to get a representation of all the characteristics in which we are interested. So, the only advice I can give is to grow as many as you have time and space for. Sometimes I grow 35 of a cross, sometimes only 7. I usually grow 10-20 of a species rhododendron if that many germinate, but that's because I'm in a species study group. When I transplant, I don't pick just the biggest and healthiest, but rather a cross-section of what's available.
When all seedlings have been transplanted, put the lid on the box. Do no watering in, no misting or spraying. Label the box and make a diagram in a notebook for the layout of seedling seed numbers and/or rhododendron species or hybrid varieties in the box. Now locate a board on which the box will sit comfortably, and weigh the combination of board and seedling-filled box on a platform kitchen scale. The storage boxes I use weigh about 8 lbs. at this stage. Record the weight and keep the board for future weighing. Regular weighing is the way to get by without drainage holes in the box. If you maintain the original weight, the medium won't get too wet or too dry.
Place the box so the lid is 4"-5" below the tubes of cool white fluorescent lights. I use shop lights with two 48", 40 watt cool white tubes. If you wish, you can use one cool white and one plant light tube. I've tried both kinds and haven't noticed any appreciable difference. I have outfitted 72" x 42" x 18" metal shelving with 4 shop lights over 4 shelves. Each light fixture is grounded and is controlled with a separate timer. (You can see that I tend to be somewhat cautious with electrical equipment that turns on and off every day for years.) Four boxes can be arranged on one shelf in this setup. However, you don't need all this. A 24" shop light or one of the commercial table-top houseplant lights would be fine for one box.
The lights are timed to turn on at 7 A.M. and off at 11 P.M. The temperature in the vicinity of the boxes is about 78°F. summer, 70°F. winter, and somewhere in between spring and fall. Allow the transplanted seedlings about two weeks to adjust to their new environment. Then start a program of misting or spraying the seedlings about every 2 weeks with a freshly made mixture of 1 level doll spoon of Benlate and level doll spoon of Miracid in 20 oz. of water. Don't use all of this on one box. It's enough for ten boxes. I give each seedling 5 strokes of the mister (fine mist). If you occasionally forget to fertilize, don't worry about it, it won't matter. As long as the box lids are kept on you should lose very little water. About once a month weigh, and spray with water to the original weight if necessary.
Let's do a little recapping here. Say you sowed the seed March 1; refrigerated them until April 1; they started germinating by April 15; and you transplanted them July 15. How big would the seedlings be by the end of the year? The answer depends, of course, on the variety. R. yakushimanum seedlings, for instance, would be perfect little gentlemen from start to finish. They stay relatively small, often do their own branching, look adorable the whole time, and by April of the next year would average 3" in diameter by 2" tall for a box full. With fewer in a box, each would get somewhat larger. On the other hand, consider a catawbiense or a maximum cross. The seedlings would probably have to be pruned in September and would still be pushing up the lid by January. Incidentally, I have pruned all manner of seedlings and have yet to find one that died as a consequence of pruning. I cut them back (with alcohol-sterilized scissors) above a leaf which is 1" to 2" above medium level. Sometimes they branch, sometimes not. You should guess from this that it is wise to plant low-growing varieties in one box and more rampant ones in another. Otherwise, give the larger ones plenty of room or they will tend to crowd out the smaller ones.
We have now arrived at another disadvantage of this procedure for growing seedlings. They tend to get too big too soon - before the outdoors is ready for them. Many of them have grown to the top of the box by December or January. You can, among other things: (1) delay starting seed until later in the year, (2) prune one or more times, (3) stop fertilizing, (4) devise a height extension for the box, or (5) start ventilation by gradually raising the lid, with the object of eventually removing it entirely. I've tried everything but (3). If you choose (5) it will entail a higher level of care and tie you down to plant sitting sooner in the overall procedure, because you will need to water more and more often. Necessity is the mother of invention, so one year when my wife and I were going on a month's trip in January and February, I made extensions for the boxes from polyethylene film reinforced with 2" x 2" wire mesh (available in hardware and discount stores). A strip of the reinforced plastic was cut to length to wrap around the box top. The ends of the reinforcing wire were joined to get a good fit of the strip around the box top and to allow the box lid to fit over the extension top. Black plastic electrician's tape was used to join the bottom of the extension to the top edge of the box. I made my extension 2" high; 3"-4" would allow even more time before you need to start the process of removing the lid to accommodate the growing seedlings. So, actually, I now use a combination of (2) and (4) when there are vigorous growers to contend with. The extensions can be removed by removing the tape and can be used again the next time. I don't put them on until the need arises because there is more water loss with them in place (4-6 oz. per week), and therefore you need to tend to them more often. Let me set your mind at rest, though. For various and sundry reasons I have had boxes lose 24 oz. of water before I got around to watering them. The plants may not have looked exactly perky, but after being watered they were perfectly all right.
By the middle to the last of February I have started ventilating the boxes so the plants will become acclimated to the lower humidity of the real world. This also gives relief to plants which are pushing on the lid. Ventilation is done gradually over a period of about a month. All it involves is laying wooden sticks across the box top (or extension top) so the box lid rests on the sticks. A 1/8" spacing is used first; then every 4-5 days another set of sticks is used, to increase the spacing to ", ", ", 1", and finally lid off. Naturally, you will have to water more often. The box will lose 8-16 oz. of water every 3-4 days with the lid off, so I'm watering every 3-4 days at this stage. I have moved from misting to spraying to pouring the water from a measuring cup in order to replace the water lost by evaporation. Water loss is determined as before by weighing the box on the board on the kitchen scale. Oh yes, I'm still misting the plants with the same amount of Benlate and Miracid about every two weeks. This brings up a question for which I have no answer. I have a conveniently located downspout from which I collect rainwater to use in watering the seedlings. If you use tap water, and it is very hard, would the accumulation of salts eventually injure the seedlings? I don't know, since I have always used rainwater. My guess is that it wouldn't. I have done some calculations based on my experiences with the procedure. An estimated 0.3g. of fertilizer per box would be added assuming fertilization every two weeks from August to May. Based on 1 00 ppm water hardness, watering the box that lost the most water would add about 0.8g. of salts for the whole time. That doesn't seem like an unreasonable amount.
Continuing the scenario, it is now the middle to the last of March. Continue watering, but as soon as weather permits move the boxes outdoors. In my locality that's the middle to the last of April. Set the boxes (by now without lids) so they get plenty of northern light but no direct sunlight for a week or so. Gradually expose them to partial sunlight. Watering needs will be much reduced now because of the cooler outdoor conditions. Protect them from rain. Most boxes will present a solid mass of leaves and the canopy will rise 0-5" above the top level of the box. The seedlings are ready to be transplanted again.
I try to get around to this transplanting in early May. The danger of a heavy frost should be past. I remove the plants from the box by placing both my hands on the medium between the plants and having someone else invert the box onto my hands. The whole contents of the box should come out in one piece, since the roots are intermingled. Now flip the mass over, root side down, onto a handy working surface. Gingerly pull the plants apart; refer to your diagram and label each one as you transplant it to bed or pot. (Don't try to remove plants from a box in this fashion if it's apparent that the root mass isn't going to hang together). I water the plants in well with tap water after transplanting.
Some seedlings are transplanted to raised beds and some to one gallon plastic pots (with drainage holes). The raised bed is outlined with cedar logs and the planting medium is about 12" deep. You should be able to get used one gallon pots from a landscape nurseryman for a very reasonable price. I wash and sterilize them before use. I have used all kinds and combinations of planting mediums and haven't discovered any magic formula. In my opinion you can be successful with whatever humusy materials are available to you. Just to give you ideas, though, here are my typical formulas (all by volume):
39% pine bark mulch
29% good dirt
19% 1 yr. old leaf compost (mostly oak)
3% sphagnum peat
One Gallon Pot
35% leaf compost (same kind)
32% pine bark mulch
16% pine bark mini nuggets
10% good dirt
I have a hunch, but no experimental proof whatsoever, that planting medium containing some dirt will speed the plants' adjustment to planting in the garden at a later date. At that time I use a mix very much like the raised-bed mix. The dirt-containing mix will retain water longer, which is an advantage in dry weather but a disadvantage in very wet weather.
There are umpteen different ways of handling fertilization from this stage on. I haven't experimented enough to be able to recommend a best way or even a better way - this is just my way. I don't fertilize when I transplant. The leaf compost has some 6-12-12 fertilizer in it which had been used to help the composting process. Toward the end of May I'll lightly spray the plants' foliage with a mixture of 1 tablespoon of Miracid in 1 gallon of water. The next year I'll give each plant about tablespoon Miracid in a small amount of water, plus a solid application of teaspoon of triple-phosphate and 2 tablespoons Agrinite (reprocessed sewage sludge. Provide the bed or pots with partial shade - either high overhead shade from trees or man-made shade such as from lath. I set my pots on a patio where they are shaded by trees in the morning and by the house in the afternoon. They get only about an hour of direct sunlight, around noon, but a fair amount of light from the northern sky all day. I water during dry spells in the summer and fall. If the pots get too dry, water will run through them without really wetting the soil. Even after watering, the pots will feel light when you pick them up. If this happens, immerse the pots in a tub of water until the soil is thoroughly wetted. As for fungi and insects, there's no use in my attempting to cover those. My bugs and your bugs won't be exactly the same anyway.
I will mention one last thing, which worried me when I first got started. That's the question of what to do with or for the plants during their first winter outdoors. If you are like me you will have a mixture of plants; some presumably cold hardy, some borderline cold hardy, and some unknown cold hardy. The plants become more cold hardy as they get older, so I usually give them some protection during their first winter. There have been years when the bedded plants had to fend for themselves, though. You lose a few more that way. One method of protecting bedded plants that has worked well for me is to lay across the bed several 2" x 6" planks, supported by the border logs. Run across the bed: lath fencing, supported by the planks. Run down the bed: roofing felt, supported by the lath fencing. Make some nail holes in the roofing felt to allow some rainwater to seep through. Anchor it to wood with nails or rocks. Don't cover the bed too soon or Indian Summer will bake the soil and desiccate the plants. The last of November is soon enough in my area unless it is an unusually cold and early winter. I place the pots in enclosures made from landscape timbers or cross ties and covered with fiberglass reinforced plastic panels. This is done in late November also. The pots sit nested on the ground, and are not watered or tended in any way until spring (April). My area, you should know, has October 15 as the average date of earliest frost, April 15 as the average date of latest frost, and an average minimum temperature of 0°F. For the last five years the minimum temperature has averaged more like -5°F. Our coldest temperature on record was -15°F. until we reached a new record low of -21 °F. on January 21 of this year (1985). The damage to young plants from this record freeze won't be known until spring. I do know that flower buds have been severely damaged on all my rhododendron, including 'Roseum Elegans' and R. carolinianum .
I don't expect anyone to duplicate this procedure. I've gone into such detail in order to at least give you ideas and at most allow you to follow it in general and modify it to suit your own needs as you go along. Try growing a few rhododendron from seed. You don't have to grow a field full or a bed full. I think you will enjoy it. Looking forward to seeing what plant habits they will develop, their leaf forms, their overall performance, and finally, all the characteristics associated with their bloom will stimulate and maintain your interest year after year. The seed exchange makes it possible for any ARS member to obtain seed for no more than one dollar per packet.
The storage boxes used for growing seedlings can also be used for rooting cuttings. An account as detailed as that for growing seedlings wont be necessary, but I will touch on a few deviations from the usual methods and some cautions about this procedure. In general, the procedure is a modification of that suggested by Leach in Rhododendrons of the World .
Use the same sanitary precautions and the same kind and amount of ingredients in the boxes as when growing seedlings. Twenty-four rhododendron cuttings or thirty-five azalea cuttings are stuck in each box. My cuttings are taken in early to mid-July. I believe timing is important, but not critical, in that it will influence the yield of rooted cuttings. Follow the general advice of taking them neither too early (still very limber) nor too late (considerably beyond the rigid state). As you take the cuttings, identify each one by writing its name or a coded designation on a leaf that won't be removed. Use water resistant ink, such as in a Sharpie pen. Trim the leaves and stem and wound the stem in the generally recommended fashion. As you prepare each cutting, throw it into a bucket containing 1 level tablespoon of Benlate and 1 heaping doll spoon of a detergent such as Tide in 1 gallon of water. When all the cuttings are in the bucket, leave them to soak for at least 15 minutes. Then pour off the Benlate suspension and wash them once with water. Next add a solution of 100 ppm of 3-indole butyric acid (rooting hormone) in water, enough so the cuttings are entirely immersed. Allow them to soak for 9-18 hours, whatever is convenient, at room temperature. Remove them from the 3-indole butyric acid solution and carefully stick each cutting into its place in the rooting medium. Prepared holes in which to stick the cuttings are not necessary. Watering in is not necessary. To prepare 1 gallon of 3-indole butyric acid solution containing 100 ppm of the acid do the following. Dissolve 0.38g. of the acid in 5 ml. of ethyl alcohol or its equivalent, such as vodka. Pour this solution into 1 gallon of hot water (out of the hot water tap). Use several alcohol rinses to transfer all the 3-indole butyric acid. Allow the solution to cool to room temperature and use it to cover cuttings for soaking. I use 50 ppm 3-indole butyric acid for azalea cuttings treated the same way.
I've tried to make this report as complete as possible so you will have some ideas about where you can get supplies and how you can execute some of the directions. In this vein let me give you some ideas about 3-indole butyric acid. It is available from Eastman Organic Chemicals, Eastman Kodak Co., DC Special Products, 2400 Mt. Reed Blvd., Rochester, NY 14650. However, I quote: "Eastman Organic Chemicals are not intended for or sold for household use. These chemicals are intended for strictly scientific chemical work such as research, control and analytical work in a laboratory, either educational or industrial, or for industrial applications in a plant." (All inclusive government regulations as you may guess.) Eastman Organic Chemicals requires orders to be written on a school or business (such as a nursery) letterhead. I have been dispensing from one 25g. bottle for many years. An alternative is the potassium salt of 3-indole butyric acid. According to Norman Beaudry in an ARS regional talk a few years ago, this chemical is available from ICN-K and K Pharmaceuticals, Cleveland, OH 44128. I don't know what their ordering policy is. The potassium salt should be equivalent to the acid in rooting effectiveness. It is very water soluble and wouldn't have to be dissolved in alcohol first..
Now let's assume that you don't have access to an analytical balance either directly or through a friend. How are you going to weigh 0.38g. of 3-indole butyric acid or its potassium salt? Where there's a will, there's a way. Take a 12" ruler or similar flat stick. Attach a 3 oz. size paper cup to each end of the ruler with a thumb tack. Tie a string around the middle of the ruler and slide the tied portion back and forth until the ruler balances when held by the string. In one cup place a 3" x 3" square of heavy duty Reynolds aluminum foil (approximately 0.38g. in weight) and load 3-indole butyric acid or its potassium salt in the other cup until the ruler balances. You get the general idea, I hope. In three such weighings I got 0.36g., 0.34g., and 0.36g. That's close enough.
I used to soak only the stems of the cuttings, and used 150 ppm of 3-indole butyric acid. Several years ago Russ Haag asked me what would happen if you soaked the whole cutting. That seemed like a reasonable question, so I ran an experiment to find out. I took 8 cuttings each of 3 different hybrids. Half of them were stem soaked and the other half were totally immersed. In this particular experiment 20 out of 24 rooted and there was no difference in percentage rooting or size of root ball for the two methods. From then on I started soaking the whole cutting because for me it is the easier method. The only adverse effect I have noticed is that the central growth bud on some of the cuttings dies and turns brown. However, that doesn't affect rooting, and sometimes gives you more than one shoot when new growth starts. You could undoubtedly use a hormone powder treatment with the storage box procedure but I haven't tried it.
My rooting percentage for rhododendron cuttings for the last six years varied from a high of 85% to a low of 64%, with an average of 72%. You wouldn't want to start a nursery business based on these results, but they are adequate for the hobbyist. You also have to consider that this includes all kinds of hybrids and species rhododendron. Do the figures mean that if you start with three cuttings of a given variety, two will root? No! Murphy's Law comes into operation. If you are particularly interested in rooting a certain variety, perhaps none will root. On the other hand, all three cuttings of some ho-hum variety are apt to root. Actually, most of the time I get at least one rooted cutting out of three, even the hybrid 'Nestucca.' Since azaleas are easier to root, my rooting percentage for them varied from a high of 100% to a low of 70%, with an average of 88%.
I have digressed from the procedure. The cuttings have already been stuck. Now we put the lid on the box and weigh the box on a board on a platform kitchen scale. Record the weight and make a diagram in a notebook of the location in the box of the cutting varieties. Place the box outdoors where it will get plenty of light but no direct sunlight. I started out trying to root cuttings under fluorescent light indoors. Many years ago a comparative experiment taught me that it worked very much better to root them outdoors. I believe that the difference between day and night temperatures outdoors, with the attendant water condensation on the underside of the box lid, gives an atmosphere more conducive to their remaining healthy and rooting. The only attention you have to give the cuttings now is to check occasionally to see if a caterpillar has hatched from an egg and is eating the leaves, or if some cutting has developed stem rot (remove it), or if you need to spray for fungus attack, etc. If so, take appropriate action. Before the first heavy frost take the box(es) indoors and place it (them) under fluorescent light alongside the seedlings if you are also growing them. From this point on they are treated just as previously described for the seedlings. I don't start fertilizing until after they are brought indoors. They will start new growth in December or January and will put on one or two flushes, depending on how much head space is available in the box or extended box. I pot them in one gallon pots at potting time.
I hope you will give this or some other procedure a try. Rooting cuttings is a cheap and fun way to add to your collection or beautify your garden with rhododendrons, azaleas and companion plants. Yes, they too can be rooted.
Editor's note: This article arrived too late to be included in the last issue along with all the other articles on growing from seed. I am including Russell Gilkey's article in this issue as he also covers propagating from cuttings.
Accelerated Propagation Of Rhododendrons
Weldon E. Delp, Harrisville, PA
Rhododendron and azalea seeds are among the easiest to grow. No stratification is necessary. They can be sown as soon as they come out of the seed capsule or held over as long as they are kept cool and dry.
Delp Seed Germinating Mix:
1 cu. ft. Plaster Grade Perlite
1 cu. ft. Peat Moss (screened thru " hardware cloth)
1 oz. dry Aqua Grow
Firm mix in 4" square plant bands. Pour scalding water on bands containing mix with a sprinkling can, and let set overnight. The following morning, place 5" plastic labels on opposite sides of plant band. (One label is to contain seed identification.) Sprinkle seed on top of mix. DO NOT COVER SEED. Place plant band containing seed inside a freezer bag and close with a tie. Place containers where they will receive 70-75 degrees F. bottom temperature and give them 18 hour day lengths. No further care is necessary until seeds have germinated.
Group of seed in bands under lights
Photo by Weldon E. Delp
As soon as the roots have gone into the mix, gradually give more air by opening bag. After one week, remove the freezer bag completely. At this point, mist the seedlings to keep medium moist.
When the first true leaves form, it is time to transplant the seedlings.
Seedlings ready for transplanting.
Have first true leaves
Photo by Weldon E. Delp
Delp Mix For Seedling Flats:
1 cu. ft. Michigan Peat screened through " hardware cloth
1 cu. ft. Peat Moss screened through " hardware cloth
1 cu. ft. coarse Perlite
2 oz. dry Aqua Grow
teaspoon FTE 503 (Peters)
2 oz. Dolomitic lime
2 oz. 20% Super Phosphate
2 oz. Long Last Fertilizer (21-15-15)
1 oz. 10% Chlordane Granules
Formula For Long Last Fertilizer:
15 lbs. Potassium Nitrate
15 lbs. Magamp (medium grade)
15 lbs. Diamonium Phosphate
15 lbs. Muriate of Potash
40 lbs. Urea-Form.
I transplant into flats on 2" centers and induce rapid growth from January until June by maintaining a night temperature of 72-75 degrees F. I give them at least 18 hours of daylight. This I do by using 60 watt bulbs spaced 30" apart and 20" from plants. After June 21st, the plants are kept without the extra heat and light, and are left to go into normal dormancy in the fall. After dormancy, transplant into one gallon containers.
Prepared flat for transplanting
Photo by Weldon E. Delp
Delp Mix For Growing On In One Gallon Containers:
3 cu. ft. Delp basic soil mix
1 cu. ft. Peat Moss
1 cu. ft. coarse Perlite
lb. 20% Super Phosphate
⅓ lb. Dolomitic Lime
2 oz. dry Aqua Grow
1 oz. 10% Chlordane Granules
Delp Basic Soil Mix
2 parts clay soil
2 parts humus
2 parts Michigan Peat
1 part coarse sharp sand
Following Is Formula For Soil-Less Mix:
(As good as Delp Soil Mix)
16 oz. of 21-15-15 Long Last or Osmocote 18-6-12
3 oz. of 20% Super Phosphate
6 oz. Dolomitic Lime
6 oz. Gypsum
1 oz. Peters 503 Micro (5 teaspoons)
6 oz. Aqua Grow
1 oz. Chlordane (10%) Crystals
ADD TO LB. OF ABOVE:
3 cu. ft. Pine Bark
1 cu. ft. Peat Moss
1 #10 can Michigan Peat
1 #10 can Coarse Perlite
(Makes four cubic feet)
Seedlings at time to transplant into gallon
containers. These are to be put back under
lights to produce buds.
Photo by Weldon E. Delp
After transplanting into one gallon containers, the plants can be forced to bud by putting them in the greenhouse and keeping them under the same conditions as seedlings.
Seedling rhododendrons will produce flower buds on the fifth growth cycle. After budding, let them go dormant in a cool greenhouse (Below 50 degrees F., and they will flower normally in the spring.
Transplanted after budding in one gallon
into a five gallon container.
Photo by Weldon E. Delp
Delp Mix For Growing On In Five Gallon Containers:
Use same mix as for gallon containers, but add lb. Magamp. Transplant these during April, May, and June. This Delp mix for growing on in five gallon containers is for rhododendrons only.
Showing my cold house full of five gallon
container grown plants in bloom in spring.
Photo by Weldon E. Delp
Some of the additional articles on propagating from cuttings which have appeared in recent copies of the journal are:
Propagation and After Care of Rhododendron Cuttings by Dr. R.L. Ticknor, Vol. 36, #2
The Propagation of Hybrid Rhododendrons from Stem Cuttings - An Historical Review by James S. Wells, Vol. 36, #4
Ground-Air Layering Revisited by Mark Konrad, M.D., Vol. 37, #1
Light Colour and Indol-3-y1-butyric Acid Soak Time Effects on Rhododendron Cuttings of 'Blue Tit' and 'Dora Amateis', by Lisa and Nicholas Yarmoshuk, Vol. 37, #4
Energy Conservation in Rooting Deciduous Azaleas by Elizabeth K. Cummins, Vol. 38, #1
Effect of Terminal Bud Removal on Rhododendron Cuttings by B.C. Strickland and C.J. French, Vol. 38, #2
Rooting Evergreen and Deciduous Azaleas by Mark Konrad, M.D., Vol. 38, #2