Many articles have been written about growing Rhododendrons from seed-some excellent, some very basic, and some confusing to the layman. Here is yet another we would like to call "The Willow Garden Method".
Our aim is to try and grow hardier and more beautiful plants than are presently available in this area (Atlantic Canada). We obtain most of our seed from the ARS Seed Exchange each year. The packets are stored in an airtight jar in the refrigerator from spring (when the seed is delivered) until fall.
We start our Rhododendrons during the first two weeks of October. Our growing area is the basement of our home where we have two growing cabinets each with four shelves. A two-tube 48" fluorescent fixture with cool-white tubes is suspended about one foot above the level of the trays. Each shelf will accommodate five propagation trays.
Our Growing Medium:
20 liters old, coarse sawdust or bark, sifted through a 1/2" sieve
15 ml. Superphosphate (0-40-0)
(newspaper) to wick away excess moisture.
Germination will occur in 10-20 days and by about 8-10 weeks most seedlings will have developed their first true leaves. During this time nothing much needs to be done except to perhaps pluck out bits of seed debris that may show signs of mold or to thin seedlings, if sown too thick. Inspect periodically, if necessary gently water, then reseal the bags.
When most seedlings have their first true leaves start poking a few holes in the bags to allow air in and to reduce the humidity. This will prepare them for the "outside " world. Make the holes bigger over a week or two until you can finally open the bags completely. The humidity in our growing area is seldom higher than 50 percent.
Transplant the seedlings into 6-cell packs, using the same mix and carefully labeling each seed lot. Prick out plants carefully, grasping by the true leaf and place one plant / cell. Place packs in trays with water/fertilizer mix as in step2. Drain and place back under lights for ~14 hours/day. We seldom mist the newly transplanted seedlings.
Do not let the plants dry out. Root systems are very shallow at this stage and drying can be fatal. We water every 4-5 days with fertilizer/rain water (15mls/ 40L water). The well water here has a pH~8.3 so rainwater has a more desirable pH of ~5.5. If possible use unchlorinated water, water only from the bottom.
Towards the end of April or early May the plants should be 1-4 inches tall and ready to be hardened off. This is done following much the same procedure as would be done with most garden plants except for minimal exposure to sun. If time or other circumstances do not allow hardening off, simply wait until outside temperatures are about the same as inside and transfer directly to the prepared nursery bed. The preparation of the nursery bed involves soil amendment with a generous addition of organic material. Place plants, in rows about a foot apart with 6-8 inches between plants. Label both ends of the row of similar seed lots. We use strips of vinyl siding, about 8 inches long, labeled with a permanent marker on both ends. The end in the soil will be protected from fading, which means you may actually be able to identify plants later on!
Water thoroughly and protect from sun. 50% shade cloth is ideal, but lattice, snow fence or brush will work. Ensure that the little plants don’t dry out during the summer. A moderate layer of mulch should be added. We use rotted sawdust/horse manure as both a soil amendment and mulch.
Remove the shade cloth by early to mid- September. Protect the plants from winter wind by erecting a two feet high shelter (of plywood, jute or plastic) around the perimeter of the bed. We now hope for snow!
Come spring some of the plants will be dead, some will look very ‘ratty’ and some will look perfectly okay. This of course depends upon the parentage of the plants. Our observations here at 'The Willow Garden' indicate that the 'dead' and 'ratty' ones are always from a cross having one parent that would be less than hardy for this area. This is, of course, a good way to cull the less hardy or those with poor root systems. In recent years we have had very little snow with many alternating freeze-thaw cycles. This is par for the course in our part of the Maritimes (about USDA Zone5). Grow the plants for a few years and rogue out the less desirable, keeping only the best to transplant to a larger area.
How many plants to grow?
We asked a well-known hybridizer how many plants from one cross to grow in order to have a fair chance at a plant better than either parent…the answer was "only one, except you have to know which one".
How lucky are we? We have grown ten thousand-plus seedlings over the last twelve years and have several beautiful plants. It is our opinion that these plants should have a rating of at least 4/4 before we will consider them for registration.
The effort to get one 'better' plant out of every ten thousand is the challenge. The dependable nature of the many species Rhododendrons is more than balanced by the undependable nature of the many crosses made by enthusiasts from around the world.
Much of the 'fun' is the growing process.
Addendum January, 2002
We have made some modifications to our growing medium during the fall of 2001. We eliminated the bark component; we suspected it had become sullied with 'dog' visits! We used a blend of commercial mix, peat moss and perlite ( 1:2:1). The commercial mix was one with fertilizer so we did not add any when moistening the blend. A soil analysis showed sufficient nutrients. We also did not use 'No-Damp' at the time of seeding. Our current seedlings are doing just fine. This mix may dry out a bit more quickly than the other, but not dramatically. The need for adding any fertilizer to the watering regime will be monitored as growth progresses.
Please note that in the original article the
proportions should be 1/4 strength (15ml per 20 liters) to moisten the
mix and 1/8 strength(15ml per 40 liters) for watering and fertilizing.
An erratum was published, but not everyone may have noticed.