Dwarf Rhododendrons from Seed

By Henry Fuller

Easton, Connecticut

Originally published May 1994
(Reprint from Georgian Bay)

We hear more and more about rhododendrons in rock gardens, and our annual seed list offers us seed of many which are suitable for rock gardens. If this seed is not wasted, if more members would grow from seed such rhododendron species as RR. yakusimanum, racemosum, keiskei, and impeditum (to name only four good ones for rock gardens) and use them imaginatively in quantity, the thought of the beauty that could be added to our gardens in a few years warms the heart. Rhododendrons make seed in abundance, and the seeds are generally not difficult to germinate. Not only can we have these most beautiful of shrubs in our gardens, but we can have them in as great abundance as we desire.

There is, however, a problem. The conditions needed for the germination of rhododendron seeds are quite different from the conditions required by most alpine seeds, and I cannot recall any of the many fine articles in our literature on the growing of alpine and rock garden plants from seed which give any attention to the germination of rhododendrons. So, without a little attention to these special needs, some of our members, who are good gardeners skilled in growing alpines, could be disappointed unnecessarily and waste precious seed when they turn to rhododendrons. But this need not to be.

Surprisingly, though rhododendron and azalea plants grow best in cool conditions, their seeds need heat for germination, heat and high humidity, without any previous chilling. They can be sown as soon as you harvest or receive them in the Fall or Winter, without any chilling, and if conditions are right most species will germinate in two or three weeks. A simple medium of equal parts of peat moss and perlite is quite satisfactory. Nfilled sphagnum moss, without any admixture, is often recommended and the seeds germinate and grow well in it. I find, however, that the young seedlings can be pricked out of the peat moss and perlite mixture with greater ease and with less injury to the fragile roots, so I prefer it. The seeds should be sifted onto the surface of the medium and not covered. Do not cover with grit, sand or anything – no matter how successful you have found this practice with alpines. Do not water them in, except with a very fine and gentle mist, so as not to wash the seed down into the medium.

I generally use square plastic pots, capping each with a small polyethylene bag; a pot three and one-half inches across the top will be fitted snugly by a normal sandwich bag. Sometimes I use small plastic flats, inserting each into a larger polyethylene bag held up by plastic pot labels. Thus simply can high humidity be preserved – and this is absolutely necessary; drying of the surface of the medium can be fatal, quickly, to the uncovered seed.

A little more trouble must be taken to preserve a constant gentle heat. Experts say 75F is perfect, but anywhere in the seventies will do, though they must not be baked and it is worth repeating that the surface must never dry. Perhaps others can find warm window sills, or warm closets, tops of furnaces not too hot or other natural spots in their houses, or somehow germinate their rhododendrons with their lewisias and gentians, but I have always failed in this. However, once I determined to make a simple propagating case especially for my rhododendron and azalea seed, this turned out to be very simple, and I have found the seed the easiest and surest and almost the quickest to germinate.

I have neither greenhouse nor alpine house, my basement is not warm, and I am a very poor carpenter and no electrician. But I am capable of finding or making a wooden box of a size to fit under a fluorescent light, which come in all sizes, in the basement. Even I am capable of coiling in the bottom of the box a small and inexpensive soil-heating cable, and of covering the cable with a few inches of moist peat moss and perlite. Stand pots or flats on the peat moss, cover the box with polyethylene, turn on the light, and wait with confidence. It does not matter whether the fluorescent light is under or over the polyethylene. The seed will sprout so thickly that you will always wish you had planted less seed more thinly. At least I do; you may have more faith and self-control and plant fewer seed.

The seedlings can be pricked out as soon as they have two or three true leaves. They will then need less heat, and no bottom heat, but if you start them as early as I like to you will need some light to keep them growing, but it need not be of high intensity. I use fluorescent bulbs. The alternative is to delay germination until Spring, but then your seedlings will be very small when Winter comes again, and it will take a year or more longer to grow them into blooming size plants. You can buy an inexpensive timer to turn off your lights six or eight hours every night, or turn them off when you go to bed and turn them on when you get up.

When thinking of rhododendrons and azaleas for rock gardens, it is natural to think first of the dwarfs and semi-dwarfs and small-leaved varieties. But all except the smallest of rock gardens need shrubs and trees of all sizes as backgrounds, dividers, windbreaks, or companions. What shrub makes a better wind- break than a hardy ground-hugging rhododendron? Or what better suggests the mountains and high places, which rhododendrons clothe all over the northern hemisphere?

If I lived in a hot desert, I have no doubt that I would try to make a rock garden of cacti, and find joy in it – but outside of the desert I find it difficult to think of a rock garden without rhododendrons and azaleas. And if, as I grow older, they tend to take over my rock garden, and my lawn too, I will not resist. I will just watch, and bless them, and give away my lawn mower.

Reprinted from R.S.C. Georgian Bay and Lakeheads Bulletin (Spring-Summer 1983)