JARS v64n4 - Sugar-coated Seeds

Sugar-coated Seeds
M. J. Harvey
Victoria, British Columbia, Canada
Reprinted from the February 2010 Victoria Society newsletter

Some people watch paint dry, others watch grass grow. Myself, I enjoy both of these but I think my greatest pleasure comes from waiting for seeds to germinate. The reason for this is that as a geneticist much of my life has been spent making hybrids - plant hybrids. I should add that I am also an amateur painter and an agrologist.

I occasionally sell hellebore plants grown from my hand-pollinated seed and I have subsequently been complimented on the really nice Cyclamen that have sprouted in the pots. This comes about because, after keeping pots containing Cyclamen seeds for a few years, I recycle the soil into general compost and seeds not then germinated sometimes proceed to do so. So this article contains hints about certain seeds that either take their time or require special conditions before they will germinate.

These plants include some of the more desirable woodland species: Trillium, Paris, Podophyllum, Epimedium, Cyclamen , hellebores, peonies and Japanese maples. If you are able to grow your own, you can obtain larger numbers of plants and save a stash of money in the process.

When you think about the nearly simultaneous germination of crop and annual flower seeds you realize that this is an artificial situation, the result of unconscious selection over the years by the simple act of cultivation. Seeds that fail to germinate with the majority do not produce seeds for the next crop and so do not pass on their genes to the next generation. Darwin, 150 years ago, called this artificial selection but, unlike his examples of the breeds of dogs and pigeons, it does not require any thought on the part of the grower - it just happens automatically. New plant introductions to our gardens have not had a long history of cultivation so you should not expect an easy ride. They come up on their own timetable and usually anything but simultaneously.

The torrent of new and unfamiliar species coming into our gardens, largely as a result of the relaxation of conditions in China, has resulted in the greatest Golden Age horticulture has yet experienced. These plants are often in short supply and propagating your own can be advantageous. Following are instructions to give you a greater chance of success - but no guarantees.

Stratification
This is a germination technique developed in European nurseries in the 19th century for awkward seeds. In a cold frame or outdoors a layers of sand would be sprinkled with seeds followed by more sand, then seeds and so on until all were sown. The analogy with the layers in sedimentary rocks - strata - inspired the name. This procedure was started in the fall and the pile left to weather until germination started in the spring.

Today we use the same process but with things such as plastic bags containing slightly dampened peat or Perlite with the seeds in the fridge. My favorite method (actually dictated by my wife, something to do with dirt in the fridge) is to sow the seeds in pots as soon as they are ripe (or available) in a peat-Perlite mixture topped with sand. I put the pots into plastic bags and keep them outside in a cold frame or an unheated shed.

Stratification mimics what occurs in nature. It takes 4-6 months and sometimes two or more winters. I have heard advice such as "Throw the seed packet into the fridge (or freezer) for a week or two." This is false advice; if it works, those seeds did not require stratification.

Hellebores
These have endospermous seeds, that is, the seeds are shed from the parent before the embryo inside has developed. Thus "postshedding ripening" is required. Endosperm is a nutritive tissue that the embryo has to absorb before it can germinate. In non-endospermic seeds such as peanuts and beans, the embryo has completed this process by the time the seed is shed and one can see the cotyledons when the seed is split open. In contrast in endospermous seeds, the cotyledons develop from very small to nearly filling the seed during the time the seeds are in the soil.

In the case of hellebore seed, sow it as soon as it is shed from the plant, or at least within a few weeks. This gives the embryo time to grow to full size inside the seed over the summer and fall. When I stick to this timetable, they all germinate by December. If however sowing is delayed, just keep the pots for a couple of years; the seeds usually germinate after the second winter. Strictly speaking hellebores do not require stratification, but treat them as if they did.

Cyclamen
In all species of Cyclamen except the florist’s cyclamen C. persicum , the fruiting capsules are brought down to soil level after flowering by the coiling of the pedicel (hence presumably the name cyclamen). Whether they flower in fall or spring all species ripen in summer when ants are at the busiest. As the capsules crack open, ants eagerly gather the sugar-coated seeds and take them to their nest. (So no, breakfast cereal manufacturers did not invent sugar-coated food.) The ants do not consume the seeds but only clean off the coating and abandon them either in the nest or at a distance.

Fresh Cyclamen seed should be soaked in water for a day or two and sown fairly deeply in a sterile mix. I once came across some deeply buried seeds with eight-inch long first leaves pushing through the soil like delicate threads. Some growers advocate keeping the pots in the dark but opinion is out on the need for this. Old seed can be extremely irregular in its germination. Soak the seeds in water and keep the pots for at least two years.

Trillium
Collect the fruits as they start to ripen in summer, break them up into a container of water and allow them to ferment for a week or so. Sieve out the seeds under running water and sow immediately. It is best never to dry Trillium seed. Treated this way, our West Coast T. ovatum may, emphasize may, germinate in the first spring, but it usually takes two winters, as do almost all the other species. In 2009, my neighbour promised me the seeds off his clump but I was too late; wasps had carried off the seeds. Another case, I suspect, of a sweet tooth.

Paeonies
These have probably the most complicated germination mechanism known. The seeds are endospermous and germinate in two stages over two years. In the first winter, the radicle (root) emerges and as the temperature warms up for the first spring the embryo starts to grow but does not make an appearance. During the second winter, the embryo itself stratifies and as the temperature rises at the end of the second winter, the first true leaf appears, although the cotyledons themselves usually remain trapped in the seed case, their job of absorbing the endosperm being complete. In the case of the big-seeded yellow tree peony P. ludlowii ( lutea ), it will occasionally germinate in its first spring.

Postscript
My grandfather came to live with the family when I must have been about four years old. He looked after the garden. He bought packets of lettuce, radish and flower seeds for his little grandson - French Breakfast radishes and Tom Thumb lettuce - the names are embedded in my memory. I must have been four or five years old when I sowed my first seed under this tutelage. Let me se - that means that I have been growing seeds for about 70 years. Parents, beware what your youngsters learn early; it can have a long-lasting influence. A pity my granddad did not play guitar, but then of course I wouldn’t have written this.