Middle Atlantic Chapter
Rhododendrons and Azaleas from Seed
Rhododendron and azalea seed germination requires moisture and some warmth. Rhododendron and azalea seedling growth requires light, moisture, warmth, and some fertilizer.
Cool white fluorescent, about 8 inches above top of seedlings for 16 to 24 hours a day. While light is not needed for seed germination, it is needed for seedling growth. Either place seed germination containers under lights or move the containers under lights as soon as seedlings start to appear. Keep seedlings out of all but north facing windows.
Maintain 70 to 75 degrees F. for best germination, cooler temperatures will slow down germination and/or seedling growth. Do not increase the heat to the point where it dries out the growing medium.
The moisture in the seed bed and seedling planting medium should never dry out, nor should it ever be wet to the point that water can be squeezed from the medium. This is the most critical factor in both germinating Rhododendron seed and growing on young Rhododendron seedlings.
For seed germination the growing medium needs to have the following qualities; moisture holding capacity, drainage, and be fine enough to support very small seeds on its surface. The preferred material seems to be milled sphagnum moss, however, there are many possibilities. Much less critical is the growing medium for new seedlings. All of the above qualities except for fineness are important to growing seedlings. For seedlings equal amounts by volume of peat moss and horticultural perlite are satisfactory, but there are many other recipes, experiment.
Almost anything will do for seed germination as long as it is clean, maintains high humidity, has about 3 inches of depth when closed or covered, and has a clear top or cover. Containers for growing seedlings can be just about anything also, however drainage is critical. It is easier to manage the water needs of seedlings when the seedlings are planted about 2 inches apart in all directions in a large container or flat that is about 2 1/2 to3 inches deep and filled with planting medium to the top rather than to plant each seedling in it's own small pot.
Fungus grows quite well under the same conditions needed for Rhododendron seed germination. Frequent observation of the seed germination and seedling containers will indicate whether a fungus is present. One type frequently found in seed germination containers looks something like fine grey hair. Control with a fungicide suitable for seed rots and damping-off diseases, (Captan is one such fungicide). Read the label on the fungicide container and follow at all times the safety instructions.
For new and young seedlings a weak, 1/4 to 1/3 strength, acid type, fertilizer applied every other watering is sufficient. There is room to experiment. Discontinue fertilizing by early July so that new growth can harden off before cold weather. However, if the seedlings are to be kept inside growing throughout the winter, fertilizing can continue.
Seed Germinating Procedure
Fill the container with 1 to 1 1/2 inches of moist milled sphagnum, not sphagnum peat moss. Very gently firm and level the sphagnum. Sow the seed on the surface of the sphagnum. Do not sow the seed to thickly. Forty to fifty seedlings in a 4 by 4 inch container is about right. If you get 100 or more seedlings in that size container you wont have to think twice about how much seed to sow the next time. Do not cover the seed with the medium. Settle the seeds on the surface of the germinating medium with a fine water mist, when the seeds stop moving you have misted enough. Cover the container with a clear top, one that can seal the container sufficiently to maintain 100% relative humidity. There should be about 1 inch between the medium and the top of the container. This cover will remain over the container, except for water or fungicide maintenance, until seedlings appear. Do not forget to take into consideration warmth and light factors. When seedlings appear, in 2 to 8 weeks, begin to mist lightly with a dilute fertilizer solution. As the seedlings begin to get their first true leaves, remember cotyledons were the first to appear, gradually, over a week or two, expose the seedlings to the environment outside the germinating container. When these hardened off seedlings have 2 to 4 true leaves they are ready to transplant. Do not let the germinating medium dry out or become soggy.
Transplanting and Growing Seedling Procedure
Take a container that has drainage holes and can hold from 2 1/2 to 3 inches, in depth, of growing medium. Place the moist growing medium in the container, and level and very gently firm. Using something like a nut pick, gently tease a seedling from the germinating container, holding the seedling by a leaf. Open a slit or hole in the growing medium and place the seedling roots in the hole and close. Being sure to close the bottom of the hole around the roots. Space seedlings about 2 inches apart. When the container is full of seedlings water the seedlings in with the 1/4 to 1/3 strength fertilizer solution. Protect the transplanted seedlings for a day or two after which they can go back under the lights for 16 to 24 hours a day. When danger of frost is past the container can be placed on the north side of a house or under high shade. Remember, if plants are to remain in a cold area for the coming winter, stop fertilizing in early July so that the new growth has an opportunity to harden off. Continue watering as needed. Seedlings may either be transplanted in the fall into individual pots or allowed to remain in the container over winter and transplanted into individual pots in late winter or early spring, or they can be planted in a nursery bed for a year or two. Native deciduous azaleas, if watered and fertilized can produce limited flowers in 3 years from seed germination.
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