WHAT Perennials Grow Best in Banff? Check Hardiness Zones First.
We are limited to varieties that are adapted to withstand our long, cold winters. A plant’s cold-hardiness is indicated by its Hardiness Zone number: the lower the number, the colder winter temperatures it can take. Canada has mapped out corresponding Zone ratings across the country that go from 0 (think Nunavut) to 8 or 9 (as on Vancouver Island).
In round numbers Banff is in Zone 2, so any plant rated as hardy to Zone 2, or lower, should do well here – as long as it also gets its particular sun/soil/moisture requirements. Sometimes you will see the Zones broken down into subzones; according to www.planthardiness.gc.ca, Banff is moving from 2b (min Temp -45 to -40 degrees C) to 3a (min Temp -40 to -35 degrees C), as our globe warms. In addition to minimum winter temperatures, the Canadian zoning system also takes into consideration a region’s length of frost-free period, summer rainfall, maximum summer temperatures, maximum wind speeds, snow depth, and the effect of elevation.
Matching your plant Zone to your location Zone is a good starting point. But some spots within each Zone are always going to be better or worse than others; there is lots of microclimate variation. So, for example, in Banff you could have success with Zone 3 plants, or maybe even some Zone 4 ones, by taking advantage of an especially warm, sheltered location, and by using good mulching techniques.
WHEN Can We Start Planting Annuals? Consider the last frost date.
Nobody knows for sure exactly when to expect the last frost of spring, but here are some predictions based on past data. The Farmer’s Almanac says Banff’s probable last frost date is June 23! Plantmaps.com is a bit more optimistic, giving a last frost date somewhere between June 11 and June 20. So if you want to start putting some colour out there earlier (and who doesn’t?), here are some suggestions:
Start with the more cold-tolerant plants that can take a light frost: pansies, violas, dianthus, snapdragons, sweet alyssum, dusty miller, calendula.
Bring your annuals inside or into your garage when frost is predicted. Of course this only works for planters, baskets, and plants that you have bought or grown but not yet planted out.
When temperatures are forecasted to drop to zero or below overnight, cover your plants with a blanket or cloth sheet (not plastic as it doesn’t work well as an insulator).
Unless they are particularly cold-sensitive (like coleus or basil) most plants can handle a light covering of spring snow, which acts as an insulator. Tall plants may need to be protected from a heavier snowfall.
HOW LONG Is Our Growing Season? Calculate the days between last and first frost dates.
The Farmer’s Almanac lists Banff’s frost-free period is June 23 to August 19, so it could be as short as 56 days. Plantmaps.com gives Banff a range of 71-89 days, based on their earlier last frost dates (June 11-20) and later first frost dates (Sept 1-10). Anyway, our growing season is likely long enough for radishes, Swiss chard, lettuce, spinach, kale, and even beets or “Potatoes in Pots”, but probably not for pumpkins.