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what happens to seeds in the winter

Ready or Not

Q. The packets for annual seeds say to plant them after any danger of frost. How do so many annuals seem to survive the winter?

A. The packet warning is aimed at protecting the vulnerable seedlings, not the relatively invulnerable seeds.

In general, the seeds for annual plants are adapted to sprout each year when conditions return to ideal after a season of stress, whether cold or drought. The annual plant dies off, leaving the seeds as something like life rafts to carry the plant’s genetic heritage across to the next generation.

Many annual plants are prolific producers of seeds, ensuring that at least some will be in the right place at the right time, usually in spring but sometimes in autumn. Propitious conditions include not just soil temperature and texture but also moisture and light.

Some seeds can lie dormant for years until the conditions are right, and some need a period of moist prechilling, called stratification, to prepare them for germination. Others need to have their tough coatings scratched, or scarified, to sprout.

Annual plants have evolved so that those that live in predictable habitats have regular cycles of readiness to sprout, and studies have found that plants in unpredictable habitats, like deserts, have more complex cycles of nondormancy, ready to sprout in many conditions, and conditional dormancy, sprouting only in ideal conditions.

Many annual plants are prolific producers of seeds, ensuring that at least some of them will be in the right place at the right time.

Alys Fowler: why seeds need a cold snap

For many seeds, dormancy is broken by a drop in temperature. So you can leave it to nature – or cheat

Hawthorn. Photograph: Alamy

Hawthorn. Photograph: Alamy

Last modified on Fri 1 Dec 2017 15.38 GMT

S eed dormancy sounds rather appealing right now. I’d like to wrap myself up in a warm coat and spend the next few months in stasis until spring arrives. If only that was what really happens. It may seem as if seeds are just lying in the soil waiting for the temperature to rise, but something else is going on.

For many seeds, dormancy is broken not by a rise in temperature but by a drop. It’s the cold of winter these seeds are after. The season’s cycle of frost, harsh winds and bitter rains slowly softens the tough seed coat, rolling it around in the soil, freezing and then thawing again, until the seed can take up water and germinate. This is known as stratification, or cold treatment. You can tell seeds that need a cold period before germinating because they have hard bony coats that are impervious to water.

Having such a tough shell ensures that germination occurs only when conditions are right. Weather fluctuates; you don’t want your seed jumping into germination just because autumn has a few cold nights and then a warm one. It’s not spring yet and those cold nights did not represent winter. So time and temperature are the keys necessary to unlock germination for many seeds. For others it may be light, smoke, certain chemicals or spending time in an animal’s gut.

Many domesticated plants have undergone numerous selection pressures, so dormancy isn’t such a big deal. Wild plants, however, are fiercely dedicated to their dormancy methods. Common plants that require stratification include apples, sloes, hawthorns, plums and acorns, but also smaller seed from herbaceous perennials such as aquilegia, lavender, sage, sedums, perennial sweet peas, wild rose and hops.

One way to break this dormancy is to leave it up to nature. This is not the fast route, but it’s a sure one. Sow seeds outside now in pots, cover with grit (mostly so that it’s easy to weed out any interlopers) and leave them to the elements. Be patient: signs of life should appear, if not this spring, then the following. You can also make a seed bed for stratification. Use a gritty compost mix, one part grit to three parts compost. Excess moisture can be a problem, so make sure it is free-draining.

Or cheat. You can use the fridge (and sometimes the freezer), placing the seed either on a damp sheet of kitchen towel or in damp vermiculite in a freezer bag (on which you can write all the details: seed source, date, temperature requirements etc). Most seed that requires a winter chill will need between two weeks and three months before dormancy is broken. Keep checking the seeds until you see signs of life. Once they germinate, take them out of the fridge, pot them up and keep them frost-free until you can put them outside.

For many seeds, dormancy is broken by a drop in temperature. So you can leave it to nature – or cheat