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The Easy Way to Germinate Rhododendron and Azalea Seed and Grow Seedlings

by Frank Pelurie

Rhododendron and azalea seed germination requires moisture and some warmth.

Rhododendron and azalea seedling growth requires light, moisture, warmth and fertilizer.


Cool white fluorescent, about 8 inches above top of seedlings for 16-24 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 appear.  Keep seedlings out of all but north facing windows.  There is room to experiment


Maintain 70 to 75 degrees F. for best germination, cooler temperatures will slow down germination and/or seedling growth.  There is room to experiment.  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 young Rhododendron seedlings.

Growing Medium

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, moisture tight when closed, about 3 inches deep when closed, and have  a clear top.  Containers for growing seedlings can be just about anything, however, drainage is critical.  For some of us it appears to be more demanding, from a water management perspective, to grow seedlings in small individual containers, than in large flats or trays.


Fungus grows quite well under the same conditions needed for Rhododendron seed germination. Frequent observation of the seed germination and seedling containers will most often indicate whether a fungus is present (one type frequently found in seed germination containers looks something like 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, 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 inches of moist milled sphagnum.  Gently firm and level the sphagnum.  Sow the seed on the surface of the sphagnum.  Do not sow the seed too 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 won't 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 seed 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 1/2 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 seedling 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 germination container.  When these hardened off seedlings have 2 to 4 true leaves in addition to the cotyledons 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 to 3 inches, in depth, of growing medium.  Place the  moist growing medium in the container, and level and 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.  Space seedlings about 1 12/ inches apart. When the container is full of seedlings, water the seedlings in with the dilute 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.

Sow seed between the first of January and the end of March, if possible, and no later than the middle of April for ease in handling the plants in the fall.  However, if you have facilities for taking care of the seedlings, seeds can be germinated any time of the year.          


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Last updated: 08/16/02.