Get in the zone

It's been the snowiest January in the history of weather records in the region. Without a serious January thaw this year, there won't be any brave spring bulbs poking up their leaves to see what is happening.

That’s weather; it always changes, and as for climate, it has always changed too. We were under an ice cap not long ago — not long ago in geological terms. We know that thanks to climatologists and countless scientists in fields like geology, meteorology, and botany. Together they produce climate science, and if they can tell us what the climate was like thousands of years ago, they have the knowledge and science to predict the effects of a warming planet. There will be wilder swings in weather conditions — more rainfall or less rainfall, higher temperatures or even colder ones, all out of sync with the calendar.

Away from fields of science, farmers and gardeners are among the first to notice changes. Any gardener like me that takes up the challenge of planting species that are at their limit of hardiness here is likely to have more success as the world cooks. 

In my garden I have agapanthus, the African lily, planted directly in the ground, despite the belief that, like dahlias, custom says the bulbs should be lifted in fall. Because of that I always grew it in a planter that I stored indoors over winter until I grew tired of moving it. I stuck it in a flowerbed about five years ago and it has since grown and flowered just fine.

This suggests milder growing zones are creeping north, and the US Department of Agriculture agrees. In November, 2023 it released a new version of its plant hardiness zone map, updated for the first time since 2012. The map is based on 30-year averages of the lowest annual winter temperature at a given location and is used to determine which plants are most likely to thrive. The new map shows that the eastern part of the country has shifted half a zone higher as temperatures have warmed. In only ten years? That is fast.

The US map doesn’t show zones in Canada, but coming later this year we’ll have our own, updated map. Unlike the US version, our map considers factors other than lowest temperature. It takes into account length of frost-free period, maximum temperatures, snow cover, wind, January rainfall, and more, making our map more accurate.

Hardiness zones tell us what plants are suitable within a certain range. Look up a plant in catalogues, magazines, or online and you’ll usually find the zone listed, although it may not be accurate. Some sources are conservative and others overstate the hardiness of a plant. Meanwhile plant producers won’t be in a rush to make changes reflecting a zone change on their plant tags.

It’s important to remember that hardiness zones are only a guide. In my area, we were long considered zone 5a, then we moved to a zone 5b, and now it’s looking like we’ll be edging into zone 6a. This means we should be able to grow plants that wouldn’t normally survive winter.

The demarcation between warmer and colder zones on a zone map is not rigid when in spring, the guy on the warm side is mowing his lawn while his neighbour across the street is still shovelling snow. Plants in a garden in downtown Cambridge, although in the same zone, will face an easier winter than those in a garden exposed in the country near Elmira. Even within each garden there are microclimates — warmer, sheltered places that offer more protection. 

The climate may be warming but weather will be as unpredictable as ever.