An Easy Way of Growing Rhododendrons From Seed
F. W. Schumacher, Sandwich, Massachusetts
With great interest I read Peter G. Jordan's article in the October 1973 Quarterly Bulletin. I am sure anyone having time to follow the prescribed procedure will not fail to have good results. Over the last 47 years running a busy specialty seed business I was always cramped for time to attend to my pastime hobby of hybridizing rhododendrons and growing seedlings.
After a period of trials I came to a rather simple method of growing seedlings which a would-be grower should not find difficult to follow if observance is made to the following points of procedure:
1. Choice of containers. 2. Soil mixture and seeding. 3. Location of seeded containers. 4. Time of seeding. 5. Transplanting of seedlings.
For commercial growers I can heartily recommend seeding in flats, the Charles O. Dexter method as described on page 221 of the October 1973 Bulletin. For the laymen, who desires to grow only a limited number of seedlings, tin or aluminum cans make excellent seeding containers. The quart cans would do for most requirements, the gallon cans for larger needs.
The use of metal cans in preference to porous flower pots facilitates the watering problem to a great extent. For best results watering should be limited to the minimum required. It is the reaction of the plant to reach out for moisture with root growth under conditions of only moderate soil moisture which promotes maximum development in the shortest of time. Flower pots by their inherent porosity require frequent watering in contrast to metal containers which need, if handled as explained later, only one watering at a time of seeding until seeds have germinated two to four weeks hence.
In preparing the cans a number of draining holes are punched in the bottom, a layer of pot shards or a small flower pot upside down applied over the holes. As to soil mixture, I find a mixture of two parts of dry shredded sphagnum moss and one part of perlite a good one. The mixture, prepared in a bowl or on a flat surface, should he carefully watered to be moderately moist but never wet. I find hot water advisable for best penetration. You may add a little water at the time and work it in with your fingers until the medium is properly integrated. Now you take a stout stick or a hammer handle and poke in your mixture rather firmly filling container to within an inch of edge. Then sift on about an eighth of inch of the dried sphagnum moss.
As an alternate procedure you may secure from moist woods or the edge of ditches (never use moss that has grown under water) a supply of live sphagnum moss, cut it up with a shear as fine as possible and apply an eighth of an inch of it over the soil mixture in the can. The live moss as a natural medium will enhance germination especially with seed of uncertain quality.
You are now ready for seeding. Do not overdo it but aim to have about an eighth of an inch between seeds. You will best control equal distribution by taking a small amount of seed between thumb and forefinger (wipe your fingers beforehand) and release it gradually. Now apply just a sprinkling of dry moss between seeds but do not cover them. If you do the covering will form a solid mat when watered to the detriment of the germinating seeds. Remember that nature never covers her rhododendron seeds.
Then carefully apply a small amount of water to complete the seeding. It is really the art of watering which determines the success or failure of your procedure. Rhododendrons with few exceptions are not swamp plants and thrive only under conditions of moderate soil moisture. For sprinkling cans I find the pint size, available in what used to be called dime stores, the most suitable. If you use a larger can, control the opening with your finger and apply the water drop by drop. This cannot be clone if the can has a rose spray as sprinkling head.
Now cover tin with a small glass or plastic dish or stretch a piece of plastic sheeting over the top held down by a rubber band. Covers may be removed after seedlings have made their second flush of leaves.
Now to number 3, a place for the seeded containers. During the winter months in a heated room I found a suitable location on a window shelf with an eastern exposure. There is a radiator two feet below the shelf. The seeding tins are placed on the shelf on a tray covered with a thin layer of sand. To prevent heating of seeding surfaces be sure that the containers are not exposed to the sun. With a temperature about 70° F. there will be good germination in time.
There will be no need of watering until seedlings are up. For quite a few years 1 had the use of a cold pit where containers could be kept after the middle of April. As to time of seeding I had good results almost any time of the year except in November. Best and quickest germination was had with lots sown in May and June.
I have never felt the need of fluorescent lighting or the use of fertilizer in seeding containers. Good results may also he obtained sowing seeds in outside beds under shade on a seeding surface prepared with three parts of screened sphagnum peat and one part of perlite. Surface must be kept carefully watered all the time. These fine seed will not tolerate drying out at any time.
We now come to point 5, transplanting of seedlings from the tins. They may be taken from tins any time after they have their second leaves. An advantage of the moss-perlite mixture, not enriched by fertilizer, is that seedlings will not grow overly fast and may be left in the tins for transplanting at any time. There may be a thinning out of seedlings from the tins for a first transplanting with a second transplanting to follow whenever convenient. The transplants are lined up about an inch apart in the larger containers preferably plastic or wooden flats.
For a transplanting soil mixture we definitely recommend one containing loam. Loam is taken, preferably from a shady spot where it is well granulated, sifted through quarter inch mesh and mixed, three parts to one part of sifted peat moss and one part of perlite, adding 1½ ounces of super phosphate per bushel of mixture. A good mixture may also be obtained by taking up leaf mold sods about 4 inches thick from oak woods. They are passed through a shredder or broken up with a hatchet, then screened through wire mesh. Containers are filled and the soil carefully firmed with a square piece of wood.
We find an unheated cold pit the most suitable place to keep flats until seedlings are large enough, 3 to 4 inches, to go into outside transplanting beds the second or third year. For preparing the transplant beds the basic loam soil as we have it here receives a generous admixture of sand and humus material and some cotton seed or linseed meal, if available, and super phosphate for fertilizer. Sand in the mixture is important for a fibrous root system.
Seedlings will respond to various soil conditions as long as soil is friable and well drained, watered as needed. Helped along at your discretion with liquid fertilizer applications in spring or early summer, they grow quickly and are ready for field planting after a year or two in beds. We prefer to transplant from flats to beds in April but will continue through the summer months until August. Beds are boarded in and are four or six feet wide. An 8-inch wide board is used as a spacer and straight edge against which to line out seedlings. We mulch with any suitable material between rows. Shredded sugar cane, as available in feed stores, can be recommended. Saran cloth panels, three feet wide are used for shade. Panels are kept on until the end of August, then removed to allow seedlings to harden. They are replaced again with the advent of freezing weather.
Procedures as described have been employed by me for many years. If they are followed there should be a survival of close to hundred percent of the seedlings raised. By adopting procedures as much as possible to natural conditions, a grower can proceed without undue concern in quite a leisurely procession.
I have had my trials and tribulations like anyone else. If I cannot concede to optimum results in raising rhododendron from seeds I must ascribe it to the fact that it was not always possible for me to find the most suitable growing conditions in the land parcels available for the ultimate lining out of seedlings in nursery rows. I have never provided overhead shade for one to two year-old seedlings lined out in the open field and this sometimes resulted in casualties in a dry and windy season. I do find it advisable to have nursery rows between windbreaks of conifers or any other trees or shrubs to minimize the sweep of winds. To prevent setbacks as much as possible I learned to make the transplant holes rather large and to line the bottom of the hole with a layer of moist peat and to pack peat around the root of the plant before filling the hole. One precaution a novice has to observe is never, never to set plants deeper than they had been in the previous state of their development.
The transplants in the field are watered individually from a large watering can and a strip of mulch, pine needles or any other suitable material, is applied around the plants along the row. They are then left to shift for themselves without any further watering unless absolutely necessary in a spell of drought. According to space available between windbreaks, plants are spaced two and one-half to three feet apart in the row and the rows are four to five feet apart. With scuffle or wheel-hoeing for weed control a dust mulch is created between rows.