What constitutes spring, exactly? Is it a date on the calendar, or is it a change in the weather? Does spring begin when the Forsythia blooms? What the heck is an equinox? How should a gardener truly decide when it’s the right time to plant seeds? Here are some notes on spring:
A literal-minded person might consider the spring equinox (or vernal equinox) to mark the onset of spring. From this point of view, spring will commence at 8:50pm on Thursday, March 19th this year. We can say it’s precisely that time because the equinox occurs at an exact moment, and not over a period of days.
All winter, the northern hemisphere has been tilted slightly away from the sun. As summer approaches, the tilt changes so the north half of the planet tilts slightly towards the sun. The equinox occurs when Earth’s tilt is neither toward nor away from the sun. For a person living on the equator, the sun would appear to be directly overhead at this time of year. At noon, one would cast almost no shadow. It’s worth noting that at the fall equinox, on September 22nd, at 6:31am, the earth will be in the same position as it is at the spring equinox.
Spring comes as such a relief after our cold Canadian winter, that it’s tempting use the calendar date as the official guide, as though we can now ignore the snowdrifts outside the window, the frost on the windshield, or the icy draft that creeps beneath the door. As gardeners, we practically itch for the arrival of planting weather. Climate, of course, has more to do with when we can plant than the calendar does.
One useful calendar date is the Last Average Frost. For the Vancouver area, this is March 28th. Just keep in mind that it is an average arrived at by comparing the last frost dates over a 30-year period. We can have frost as late as the end of May. For those gardeners in the south of the province for whom spring just can’t arrive fast enough, bear in mind that Dawson Creek has a last average frost date of June 5th!
The last average frost date is useful because it allows growers to make an educated guess about how to time their plantings. Plants such as tomatoes need to be approaching maturity by early summer in order to make a productive crop, so we need to start them indoors around 4 to 6 weeks before the last average frost. However, the secret with tomatoes is not so much the calendar date as the arrival of warm weather so that they can be transplanted outdoors. Some years deliver a dreadfully cold, damp spring that seems to last and last, and then switch suddenly to the heat of summer at the end of June. Hopefully, 2020 will see a more transitional period with nighttime temperatures steadily increasing through April and May.
The vernal equinox marks both the first day of spring and the first day of the Persian New Year. In Iran, Nowruz is celebrated by thoroughly cleaning the house, getting back in touch with friends and relatives, and generally enjoying the arrival of a new year of growth. For gardeners, celebrating the first day of spring may make more sense than marking the first of January.