Between frosts

🕔Mar 09, 2006

It feels like spring: showers, thawing, and even a glimpse of a rainbow through a veil of mist.

In 54 years spent in the North, brief mid-winter thaws have not been uncommon, but they used to come after lots of snow and lengthy periods of temperatures well below -18˚C. The thaws were short-lived and typically followed by more snow and plenty of real winter.

In recent years that weather pattern has changed. Now the last spring frost occurs earlier, and the first fall frost comes later, making what seems like a longer growing season. But don’t get carried away! There are still factors that should govern when it’s prudent to put seeds and plants into soil in which germination can proceed safely, and in which roots can search for what they need to make growth.

Saturated wet soils are cold, even if the only moisture received has been from rain. But soils that are wet with snow melt (i.e. ice water) are even colder, and take a relatively long time to warm.

Most seeds won’t germinate until soil temperatures reach about 5˚C, and even if they do sprout, the process is very slow. If soil were to stay at that temperature level, it would take 42 days for a beet seed to sprout, and 51 days for a carrot seed to pop.

Soils don’t stay at such a low temperature for very long, but when the earth does warm to around 27˚C or higher, it only takes about five days for germination to occur, and in such warm soils seedlings don’t run the risk of rotting. Nor do they die, once germinated, from a cold soil-borne fungus that results in what is known as “damping off.”

Even if seedlings do survive an early exposure to cold soils there is another hurdle for them that can thwart their progress. They are likely to come up into a world of cool spring air temperature. Most plants just sit and stagnate if that temperature doesn’t regularly reach a minimum of 5.5˚C. All of this underlines the fact that it generally doesn’t pay to get too excited about making a very early start in the garden.

So when to start? Much depends on the physical circumstances of your garden site. What you have is what you must live with, though you may be able to physically improve a situation. Heavy clay soils are slow to warm, but that can be remedied to some extent by incorporating sand, peat, and/or other organic matter.

Mounding soil into raised beds will also help to raise soil temperature. Sandy soils, on the other hand, will warm quite quickly, but because of excessive drainage may even be to dry. That could require supplementary moisture for seed germination. Soaker hoses work well, as long as the water source is not too cold. Tepid water from a watering can may be necessary.

Site location can make a difference. A south- or southwest-facing slope, backed by a wall or hedge to create a suntrap, will enhance both soil and air temperatures. Lakeside and riverside locations often generate a canopy of fog that protects against frosts during the growing season.

All these factors explain why it’s impossible to recommend a specific start-up date that applies to all situations. If you are gardening in an area that is new to you, it will often help to pick the brains of an established green-thumb neighbour. Otherwise, err on the side of being a late seeder of your garden. You’ll still get a rewarding one if you wait until mid-May, providing your thumb is a tiny bit green.

Nature is surprisingly tolerant.

Note: Dave Havard will share his hands-and-knees look at northern gardening this spring as an instructor at the Eldercollege in Smithers. For more information or to register for Gardening for Seniors, contact Northwest Community College at 847-4461. His popular book Gardening Between Frosts is currently in its third printing. In March, Havard will reveal his personal roots in a new book: Growing up in Victoria: been there done that and a trip to Europe too.