Germinating Maple Seeds
by M.J. Harvey February 2004
At the November 2003 meeting I was extolling the virtues of Japanese Maples as trees which cast a relatively light shade, and are ideal as a cover for many types of gardens, especially Rhododendron gardens. The contrasting leaf shapes and their colour changes over the seasons add grace to the more ponderous foliage of the average Rhododendron.
There is a problem with maple seeds – they usually don’t come up. There is a real art in getting them to germinate, but mostly it involves patience.
So you plant maple seeds and they don’t come up and you think ‘stupid seeds’. Rather than cursing the seeds, think instead of what their problems are. Look at it from the seed’s point of view. The seeds are normally shed in the fall when there are still some nice warm and damp days – ideal for a seed to sprout. Let’s say they do sprout in autumn – the delicate seedlings then face a winter of frost damage, crushing snow, uprooting by floods and frost heaving, predation by mice, birds, insects, eelworms, fungi … you get the message. In other words a maple seed would have to be crazy to germinate as soon as it hits a warm damp seedbed. The same problems are faced by a wide range of temperate-region wild plants.
So what do they do? For one thing the parent plant can provide a tough outer layer (pericarp) which holds the seed in a protective cocoon until the coat rots and softens. However, most seeds contain a germination inhibition system which is chemical and physiological in nature. These systems work through a hormone cascade process acting on the ribosomes which produce the enzymes to convert the starch in the seed into sugars. Then the seed sprouts. Gibberellic acid can be used to hasten this process in most seeds although I have not tried it on maples.
Let’s get back to the point of view of the maple. They have a very sensible system which keeps them dormant over the cool, damp winter season. Should they then all germinate at the first spring zephyr? Probably a bad idea. There might be a late spring frost, an attack of damping-off fungus, a nest of mice or whatever. Better save some seeds to germinate later in the season or next year, or the year after that. So I have staggered germination. My own experience is that I have often had no germination the first spring, a good batch come the second year and a lesser number in the third year.
Yet another problem – parthenocarpy. This sounds like a Greek temple and the words are related in that the Parthenon (started in 447 BC and still standing) is an abbreviation for Athene Parthenos (Athene the virgin), and parthenocarpy means ‘virgin fruit’. What happens in maples is that some of the fruits develop without any seeds in them and are called parthenocarpic. I have read instructions about floating the seeds in water – the good seeds are supposed to sink and the hollow ones float. My advice – don’t bother. Just sow the lot, if they don’t have an embryo they won’t sprout.
So the trick to germinating Japanese Maple seeds is really long stratification. Don’t believe talk about throwing the packet into the fridge or freezer for a couple of weeks – it won’t work. These seeds need sowing in the fall as soon as they are ripe and keeping cool, say outside, in a covered pot over winter and then, and this is the bad news, probably over another winter, or two. The seed is not dead, it just sleeps very soundly. You can also use your refrigerator’s vegetable crisper for additional cold stratification.
The Good News is that when I collected seeds from Hatley Park, with the permission of the head gardener David Rutherford, I put them into ziploc bags with a little damp perlite, and they have been in my fridge ever since. So they have had their first winter of stratification already. These are on the current seed list and with a lot of luck they may germinate this year. I should add that some of the other maple species other than the Japanese are sometimes a little less picky.
Use a mixture of about equal parts perlite and peat. Cover the seeds with about 2 cm of sand. This is no problem for seedlings and they clean themselves pushing through.