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Journal American Rhododendron Society

Current Editor:
Dr. Glen Jamieson ars.editor@gmail.com


Volume 51, Number 2
Spring 1997

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Tips for Beginners - Hybridizing Notes: From Seedling to Budded Plant
Jim Barlup
Bellevue, Washington

        The seed has germinated and has been repotted during the thinning process as explained in the article "Planting the Seed" (Winter 1997 issue). Now we are ready to introduce the fragile seedlings from their protected environment to the real world. I will guide you through my way of going from 20 plants in a 4-inch pot indoors to the budding stage outdoors.
        I start my transplanting process the first week in May with 8 x 6 -inch pots, plastic markers and soil mix. The proper choice of soil is a crucial element in transplanting. There have been years when I lost half of my plants by using a mix I hadn't tested. I have tried many combinations of my own mix and almost every type of pre-mixed soil that I could find. Some soils do not drain well; others will not hold moisture. After years of experimentation, I found that a mixture of two-thirds fine bark and one-third Groco compost mix works best for me (Groco is the trade name for a local product that consists of two-thirds composted sawdust and one-third sludge, now called bio solids). You have to experiment to find the best combination for your area. In selecting your mix, remember that you are taking a very small tender seedling and plunging it into the cold soil of reality. The soil should provide a warm and welcoming home.
        Before taking seedlings out of the 4-inch pots, make sure that the soil is moist. Prepare the 8-inch pots by filling them with the chosen soil mix to within 1 inches from the top. Remove the seedlings by turning the pot upside down in your hand and tapping it. If you cup your hand the entire clump will come out without damaging the seedlings. Remove about three-quarters of the bottom part of this mix and carefully turn the clump upright. What remains is a group of seedlings with about 1 inch of peat/vermiculite mixture surrounding its roots. The individual seedlings can then be separated easily. Poke a small hole in the soil mix and insert the seedling with its root system still enclosed in the original mix. Gently tamp the new soil around each seedling. Be sure you do not bury the seedling or leave the roots exposed. I plant seven to nine seedlings evenly spaced in a 8-inch pot. If the seedlings are very small or of a dwarf variety, I plant as many as 12 in one pot. If I end up with just a few extra seedlings, I plant them in a 6-inch pot. Mark each pot with a plastic marker to identify the parentage. Push the plastic marker well below the soil line. Blue jays and crows seem to enjoy shifting white tags from one pot to another.
        Since the soil mix may be somewhat dry, water the pots after you complete about six of them to prevent wilting. Some people recommend a transplant solution. If you use one, make sure it contains nutrients. Not all of them do. (I sometimes wonder if it doesn't do more for us than it does for the plants.) The seedlings are then ready for their new home outdoors. It is important that they be protected from the cold (below 35°F) and from hot or direct afternoon sun. I set all of the new transplants in a cold frame so I can cover the seedlings if necessary. My whole year's crop generally fits into a 5 x 24-foot cold frame that is totally shaded in the afternoon by large fir trees.
        After a few days of acclimation and again during the second week, fertilize the seedlings with a water soluble fertilizer such as Miracle Gro at half strength. The third week, fertilize at full strength, then again every 10 days to two weeks. After six weeks (approximately the middle of June) discontinue the water soluble fertilizer and give each 8-inch container two level teaspoons of Osmocote 14-14-14 (3 to 4 month release). Use one level teaspoon for 6-inch pots. If I miss a pot, it soon becomes a standout with its anemic leaves. They receive no additional fertilizer until the following spring.
        The plants stay in the cold frame until late September or October when I transplant them again. I use the same fine bark and compost mix as I did originally. I transplant each individual seedling into a 6-inch pot. I expect the seedlings to be similar in size to a rooted cutting by October. (Needless to say, they don't always meet my expectations.) Some hybridizers prefer to use a 4-inch pot. By using a 6-inch pot, I can leave the seedlings in this larger pot for the next three years. A few plants may even bud during the third year. The third year they are mature and ready to be placed in the ground in October. Those precocious plants that outgrow the 6-inch pot the second year are moved up to an 8-inch pot.
        From the time the seedlings are transplanted into the 6-inch pots, I pinch heavily to ensure compact, well-branched plants. This may slow down the budding process, but that's the price you pay for a more desirable plant habit. I continually look for undesirable characteristics (weak or anemic plants, poor branching, poor foliage, etc.) and eliminate questionable plants. You have to be harsh. Of the 750 to 1,000 seedlings that are transplanted to pots outdoors, the total is reduced to about 400 to 500 plants by October.
        During the next two years, only 100 to 150 of the best plants remain. This is the group that will be planted in the ground to follow through to maturity. These plants will join my older plants that are also undergoing evaluation. All of my 4-, 5- and 6-year-old seedlings are evaluated each fall with 20 to 30 percent being eliminated on the basis of foliage and plant habit. Even though it's difficult, I sometimes eliminate plants that have budded for the first time. I'd rather not wait to see it bloom and then be tempted to keep an inferior plant. If you don't control the number of plants you grow, this love affair with rhododendrons might get out of hand.
        Fertilizing is an essential part of growing plants to the budding stage. Early to mid-March, begin fertilizing all of the container plants. Each fertilizer brand has a different analysis. Each hybridizer has a different approach. My method is to use Osmocote 14-14-14 (3 to 4 month release) for all my container plants. I use one teaspoon to a 6-inch pot, two teaspoons to an 8-inch pot, and one tablespoon to a 10-inch pot, and for larger pots one tablespoon per square foot of surface. Repeat the application in mid-June. My fertilizing program for plants in the ground is similar in timing but with a different fertilizer. I use a 10-6-4 slow release fertilizer. The nitrogen is derived from 50% sulfur coated urea and 50% ureaform (Nitroform). It also contains the necessary trace elements. This slow release type of fertilizer will feed for about three months. My rule of thumb is roughly one tablespoon per foot of height. You learn how to pick up a small handful and gauge the proper amount. The traditional way is to apply the fertilizer at the drip line. This only works if the root ball extends as far as the drip line. When I know there are no roots at the drip line, I spread the fertilizer evenly above the root ball area staying at least two inches away from the stem.
        The first application of fertilizer is during the beginning of March, the second in the first week of June and the third in November or early December when the plants are dormant. In the Northwest, we can have heavy winter rainfall (11 inches in November 1995) that depletes the soil of available nitrogen. The plant must use the energy stored in its leaves (if it had any to start with). If there is no nitrogen available in the soil and if the leaf has run out of its reserves, it will start to turn yellow. It's the plant's way of telling you that it needs help. Be careful of quick release fertilizers. They can burn or destroy plants if applied in excess.
        Look for the best soil mixes in your area and search out the best fertilizers. Your plants will reward you for the extra effort. We're striving for healthy plants with dark green foliage and happy to set buds. How exciting it is to see buds on a plant for the first time! Each spring is a season to look forward to with enthusiasm. That's what keeps old hybridizers forever young! I wish you success in your growing and your budding.


Volume 51, Number 2
Spring 1997

DLA Ejournal Home | JARS Home | Table of Contents for this issue | Search JARS and other ejournals