Let Winter Do the Work

Cold Weather Can Help Garden Seeds Get Their Start

By Blaine Howerton | NorthFortyNews.com

As Northern Colorado gardens wind down, it is tempting to think the growing season is over. For gardeners who save seeds, however, the colder months can become part of next year’s growing strategy.

Many perennial and native plants produce seeds that are not meant to sprout immediately after falling to the ground. Instead, those seeds spend winter exposed to cold temperatures and moisture before conditions signal that spring has arrived. Gardeners can imitate that natural process—or simply let Colorado’s winter weather do it for them.

The process is known as cold stratification.

Why Some Seeds Need Winter

A seed may look dormant, but it is a remarkably sophisticated package. Some species have evolved mechanisms that prevent germination until the seed has experienced an extended cold, moist period.

That makes practical sense. A seed that germinates during an unusually warm stretch in November could quickly be killed by the next hard freeze. Waiting through winter improves the odds that a new plant emerges when conditions are favorable.

That makes fall and winter an opportunity, not downtime.

One approach is to mix seeds with slightly moist vermiculite or another suitable medium, seal them in a plastic bag, and place them in the refrigerator. After the recommended cold period, you can plant the seeds indoors or outside when conditions permit.

An even simpler method is to put winter to work.

You can plant seeds in labeled pots and place them outside where they experience natural cold and precipitation. Snow is especially useful because it supplies moisture while exposing seeds to the seasonal temperature cycle they would encounter in the landscape.

As spring approaches, move the pots into partial sun and watch for germination. Once seedlings develop a couple of sets of true leaves, they can generally be transplanted into larger containers.

Not Every Seed Plays by the Same Rules

Cold treatment is useful for many species, but gardeners should pay attention to the particular plants they are growing.

Seeds with especially hard coats sometimes benefit from scarification, which means scratching or weakening the seed coat so water can penetrate it. Soaking seeds and gently rubbing them with coarse material such as sand can accomplish this for some species.

Other seeds need light to germinate. Those should remain close to the soil surface rather than being buried deeply.

The original North Forty News gardening column on seed treatments noted that members of the sunflower family may depend on light cues, while plants with particularly tough seed coats can respond well to scarification.

That is one reason labels matter. A collection of seemingly identical pots becomes much more mysterious after spending several months outside.

Start With What Already Grows Here

Winter sowing can also be an inexpensive way to experiment with plants suited to Northern Colorado.

Seeds collected responsibly from plants already thriving in your own garden offer a logical starting point. Native and regionally adapted plants are particularly interesting candidates because their life cycles developed around seasonal changes in temperature, moisture, and daylight.

Instead of fighting winter, gardeners can use it.

Prepare a few pots, label them carefully, sow the seeds, and place them where they can receive natural precipitation. Then wait.

Gardening usually rewards action — digging, watering, pruning, planting and weeding. Winter sowing offers the opposite lesson.

Sometimes the most useful thing a gardener can do is prepare the conditions and allow nature to take over.

Attribution: This story was developed from North Forty News’ 2022 gardening column, “Seed Treatments and Winter Sowing,” which described cold stratification, outdoor winter sowing, scarification, and light-dependent germination techniques.