JARS v38n1 - Rhododendrons and Azaleas from Seed

An Absolutely Up-To-Date Method of Growing Rhododendrons and Azaleas from Seed
or
If your method wasn't successful last year - try this one
George W. Ring III and Col. Raymond Goodrich, VA

Based on a Potomac Valley Chapter newsletter article by Col. Raymond Goodrich and George W. Ring, as prepared and edited by Jane Goodrich.

There are probably as many methods of growing rhododendron seedlings as there are people who grow them (over 800 members bought seeds from the ARS seed exchange last year). We suspect that most methods are successful in spite of wide ranges in types of growing media used, light exposure, growing temperature, containers and water acidity or alkalinity. The secret ingredients are: (1) an interest (which more and more members have) and (2) a little periodic observation and attention.
If you are already happily growing seedlings, you can cease reading at this point. Or if you're interested in trying - you may want to read on.
Minimum requirements for growing seedlings are:
(1)  A container 2" or more deep with drainage holes.
(2)  A growing medium 75% sphagnum peat with 25% sand or perlite, or your own special formula.
(3)  Light 150 ft. candles or more (a fluorescent bulb 10 to 12 inches from the seed bed will do).
(4)  Heat seedlings grow best between about 68° and 76°F
(5)  Water neutral to acid preferable (salty or alkaline water may be a problem), a mist sprayer is also useful.
(6)  Fertilizer Nutro, Peters 15-45-5, fish emulsion or some equivalent.
(7)  Seed your own crosses and collections, or obtain from over 1000 types available in the ARS seed exchange.
If you haven't contributed or purchased before or are a new member in the last year, you will not automatically receive a list and you should request one from Bill Tietjen. It's now just a matter of putting the ingredients together. Seed sowed in the fall can produce seedlings large enough to put outside in late spring to become acclimated and to continue growing through the summer. Proceed as follows: If the peat is very dry, soak a mixture of 75% peat and 25% perlite (or sand) overnight, then squeeze out as much water as possible by hand. Where the peat is already moist, dampening may be all that is necessary. Place the mixture in a container 2" or more deep (we prefer 4 or 5" deep) having good bottom drainage. Firm to level and sow seeds on the surface. Spray mist with a dilute solution of Captan or Benlate or a mixture of the two fungicides. Do not cover the seeds with the growing medium. Place a plastic or glass cover over the container, leaving a space for the seedlings to grow. Place under light (not bright sunlight). A fluorescent fixture with a shiny reflector (such as aluminum foil) placed 10 to 12 inches above the growing medium and left lighted 16 to 24 hours a day is suggested. Any type bulb will do, including the least expensive. At 70°F. germination will usually begin in two weeks, but some seed may take two months or longer.

Transplant seedlings as soon as possible - this is usually after the second set of leaves has appeared. This is important to get fastest growth. Space one to two inches apart, either into the same growing medium as above or a medium of ⅓ peat, ⅓ perlite and ⅓ compost. Using a fine rose sprinkler water lightly with a very dilute solution of fertilizer. Cover seedlings with a glass or plastic for a few days until root functions are re-established. Gradually remove the cover and water lightly as needed with a very dilute solution of fertilizer. The growing medium changing color to a lighter shade is a good sign of needing water. In houses having a low winter humidity, daily watering may be in order. Keep the medium damp at all times but not soaking wet. Almost all seed growing problems can be traced to keeping them too wet! If a fungus growth should appear it is usually appropriate to reduce water and dust or mist with Captan or Benlate or a mixture of the two.
If your seedlings are really lusty, you may want to transplant a second time indoors to a wider spacing. Seedlings can be moved outside after the last frost. After leaves on the trees are fully out is usually a good time. First days outside should be in a partially shaded or north exposure and during a cloudy, rainy period if possible. If not rainy, water lightly every few days at first. In a few weeks they will be perfectly happy in their new environment.

The plants are best protected from wind and sun their first winter outside in a lath house, north side of a building or cold frame. The following spring, sturdy survivors of the winter will be ready for nursery beds, lined out in a woods, or for individual containers. Surprisingly large numbers of seedlings, especially dwarf kinds, can be grown in containers in a small area. And if you have a greenhouse, or equivalent, for winter protection, the exotic vireya ¹ are easily grown in containers.
Whatever kind of rhododendrons and azaleas you grow from seed, you will probably want to experiment to determine that special growing method that works best for you. Before long, you can also be a regular contributor to the ARS seed exchange and have your hand-pollinated species and hybrid crosses grown all over the world. And, you might also be more than a little awed, and greatly delighted, with the flowering rhododendrons you raised from seed.
¹ R. vireya seed has a short viability and is distributed immediately on receipt from contributors to members who have previously submitted requests.