What to sow in autumn: seven seeds that need winter

You sow in spring. That is what you are taught, and for the vast majority of plants it is true. But there is a whole family of seeds for which spring is too late: sown in March in a heated room, they will not come up, or one in twenty will, and you will conclude that they were no good.

They do not ask for warmth. They ask to have been through a winter. And this week is the right time to give them one.

What the cold unlocks

A ripe seed is not necessarily a ready seed. In many species from temperate and mountain regions, the embryo is formed but held dormant by chemical inhibitors, abscisic acid first among them. As long as they are present, the seed can be warm, moist and in the light: it will not germinate.

What breaks them down is a prolonged period of moist cold, a few weeks to a few months between 0 and 5 °C. As they disappear, the balance tips in favour of gibberellins, the hormones that trigger germination, and the seed finally becomes able to respond to warmer temperatures. This is called cold stratification.

This mechanism is not a whim, it is life insurance. A belladonna seed that falls to the ground in September and germinated straight away would produce a three-centimetre seedling in November, killed by the first serious frost. The winter block guarantees that it will wait for spring. By sowing in autumn, you are simply putting the seed back on the calendar it expects.

Why outdoors rather than in the fridge

The method of a bag of moist sand in the fridge works, and we give it on our product pages for those who discover a species partway through the year. But if you have the choice, autumn sowing left outdoors is better, for three reasons.

First, because natural cold alternates. Successive freezing and thawing, and the variations between day and night, work better than a constant 4 °C, and for some species this alternation makes a real difference.

Second, because the seed decides. In the fridge, you choose when to take it out, and you will sometimes get it wrong: too early for a mandrake, too late for a monkshood. Outdoors, each one comes up when its count is complete, including those that need two winters.

Finally, because people forget. A bag at the back of a fridge in February ends up mouldy in May. A seed tray in a corner of the garden reminds you of itself.

The seven to sow now

Monkshood - Sow 5 mm deep in a seed tray left outdoors all winter. This is by far the most reliable method for this mountain perennial, whose germination remains slow and staggered even when well managed. Some seeds will come up in the second year.

Belladonna - Sow on the surface, without covering: this seed needs light as much as cold. It is this double requirement that explains most failures, because people think of one or the other, rarely both.

Mandrake - The slowest sowing in our catalogue. Barely covered, outdoors, and with patience: germination happens in spring, sometimes only the following spring. Never empty the tray before you have waited two seasons.

Mountain arnica - Like belladonna, cold and light: on the surface, without covering. A third requirement is added, and it is a strict one: a substrate without a trace of lime, ericaceous compost mixed with sand, watered with rainwater.

Marsh mallow - This is the simplest of the seven, and the one that is sown directly where it is to grow. Going through winter softens its thick seed coat and germination happens the following spring, without you having to do anything.

Enchanter's nightshade - Barely covered, in a humus-rich substrate, and above all kept constantly moist and cool. It is a woodland plant: a substrate that dries out for a week in March cancels the whole winter of stratification.

Ginkgo biloba - A special case, and an interesting one. In ginkgo, the embryo is not fully formed when the seed falls from the tree: it completes its development on the ground, after dispersal, before the cold comes to lift dormancy. Two stages, two reasons to sow in autumn. Sow 2 cm deep, and protect the tray from rodents: these large seeds attract them.

Those that benefit without requiring it

Two other species in our catalogue come up without a cold period, but much more irregularly. If you sow them now rather than in spring, you will get more even germination: black henbane, which needs three to four weeks of cold to make up its mind, and Indian tobacco, two to three weeks. Both germinate in light: on the surface, without covering.

How to go about it, in practice

The container. A seed tray or pot at least 10 cm deep, with plenty of drainage holes. Drainage matters more than volume: a tray soaked with frozen water rots the seeds instead of stratifying them.

The substrate. A fine seed compost lightened with one third sand, except for arnica, which wants an acidic mix, and enchanter's nightshade, which prefers leaf mould.

The position. Outdoors, exposed to the cold, but sheltered from driving rain. At the foot of a north-facing wall, under a canopy, or against a hedge. Seeds sown on the surface get washed away by a heavy downpour: lay a raised pane of glass over them, or place the tray where the rain does not hit it head on.

Protection. Fine mesh laid on top solves two problems at once: rodents, which dig up large seeds, and cats, for whom a tray of loose soil looks a lot like a litter box.

The label. In pencil, not felt-tip: ink fades in a single winter, and in April you will have a tray of seedlings whose species you no longer know. Note the name and the sowing date.

Aftercare. Two things, and two things only. Never let the substrate dry out completely, even in January: check once a month, as under a canopy a tray dries out faster than you would think. And do not bring the tray indoors during a cold spell. The cold is the method, not the danger.

Three toxic plants in this list

Monkshood, belladonna and mandrake are deadly plants, and black henbane is toxic. Sowing carries no particular risk, but handle the seeds with gloves and wash your hands afterwards: the real danger is the absent-minded gesture of hand to mouth.

Place the tray out of reach of children and animals, and choose the permanent position accordingly from now on. For monkshood, one point is worth knowing before planting: its root looks like a turnip, and fatal accidents have occurred through confusion. Never plant it near a vegetable garden.

The mistake to avoid

If you remember only one thing: do not sow these seven species in March, in the warm, indoors. It is the natural reflex, it is what you do for tomatoes, and it is precisely what does not work here. A monkshood seed at 20 °C that has not had its winter remains a monkshood seed.

If you have already missed the autumn window, there is a fallback: four to eight weeks in the fridge between 2 and 5 °C, seeds mixed with moist sand in a sealed bag, before sowing in spring. It is not as good, but it is far better than nothing.

To go further

Each of these species has its own product page, with its exact temperature, its light requirements and how it behaves as a mature plant. All of them are in our Seeds of the world collection. If you would rather skip the sowing stage, several are also available as established young plants.

Our seeds are harvested from our mother plants at the greenhouse in the Jura, or selected from growers when the species does not grow in our climate. They are untreated, and they are sold as ornamental and botanical collector's seeds.