JARS v51n2 - 30 Years with Seeds and Seedlings - Part I

30 Years with Seeds and Seedlings - Part I
Mark Konrad, M.D.
Sewickley, Pennsylvania

After growing rhododendron seeds for more than 30 years, there is the natural question to be asked: what has been learned? In my case, a great deal since I started from scratch without horticultural training. Like everything in life, there are no absolutes that apply to the subject matter.
Mostly we work by trial and error applying our adaptive and creative skills as we go along. Because personalities, skills and environments differ we often meander along different paths trying to reach the same successful goals. Apart from the philosophical differences, there are certain concepts that have a common thread inherent in good results.

MEDIUM . For germination, milled sphagnum moss is considered ideal by accomplished growers. Under highly humid conditions very little maintenance is necessary for several months prior to transplanting.
For growing on, a coarse medium which includes perlite, shredded pine bark and Canadian sphagnum peat moss as a base seems best. The pH of the mix is estimated at 5.5. A small amount of soil, preferably of the sandy type, also has a place in most instances. Rhododendrons of all sizes like good aeration with adequate moisture. Sewing your seeds directly on the prepared medium is an excellent alternative method.

MOISTURE . This is a highly critical factor. The medium should be kept damp but not soggy. A coarse medium will often help prevent over watering. Lifting your pots or flats is a good way to estimate the moisture level. Satisfactory plant physiology is dependent upon proper moisture content.

WATERING . The proper water quality is important. This becomes a significant factor in maintaining a satisfactory pH range in the medium. A pH of 5.5-6.0 should be considered a target ideal. The use of rain water, if practical and not overly acid, can be an easy solution for the small grower. Larger operations may need an expert opinion to solve difficult problems related to alkalinity and chemicals.

FERTILIZER . A general rule is to use sparingly and with caution. The needs are so small under natural conditions that any additional application could prove harmful especially if anything more than trace amounts are used. To keep the young seedlings properly programmed, perhaps it is not wise to accelerate the growth cycle too rapidly.

ENVIRONMENTAL CONDITIONS . If a coarse medium is used as recommended, adequate environmental humidity should be maintained to prevent excessive or rapid drying. The level of humidity is estimated best at 70% to 80%. Excessive heat must also be avoided with 80°F estimated to be the maximum. Some openness around the seedlings is considered the best. The more the enclosure, the more the medium should be horticulturally sterile.

Container for Rhododendron seedlings
Cardboard flats are used for 1 - and 2-year-old seedlings.
Plastic shade fabric is used for summer care
and plastic film for winter protection.
Photo by Mark Konrad

LIGHTING . Lighting should be adequate with either natural daylight, fluorescent or both. It is probably debatable which type fluorescent tubes are best for the plants.

MEDIUM ADDITIVES . According to information from our study group, the addition of organic supplements have not proven helpful in most instances. The use of cottonseed meal may be the exception. Many commercial mixes use Canadian sphagnum peat moss as a primary ingredient. Frequently dolomitic lime is added to adjust the pH to 5.5-6.5 and to provide calcium and magnesium. Often gypsum is also added as a source of essential sulfur and calcium.

TIMING . The plants do much better under natural conditions and for that reason the seedlings should be introduced to the outdoors as soon as possible. There is also an advantage in getting the seedlings as large as possible the first year so that the acclimatization to the natural state is less traumatic.

GENETIC DIFFERENCES . Some seed batches are not great performers. This makes it all the more important to have a good cultural technique established so that potential problems can be dealt with or eliminated.

PROGRAMMING . One should not hesitate in experimenting and finding a niche suitable for you and the environment. Check your plants frequently. With any significant signs of trouble, re-transplanting is often the first and best way to deal with a problem.

SUMMARY . A review of the practical, basic needs for seedling culture have been discussed. The more one can approximate the ideal, the better most seedlings will thrive.