Planting in Calgary while the ground is still warm

The Leaves

Natural Resources Canada puts Calgary at plant hardiness zone 4a on the 1991 to 2020 climate normals. On the 1961 to 1990 set the same city read 3a, and the hardiness index moved from 34 to 41 between them. The map warmed up. February did not.

The number on the map, and the number on the tag

The City of Calgary's YardSmart guides tell you to look for plants labelled zone 2 or 3 as a starting point, which is one or two steps colder than the map says you need. The University of Saskatchewan's horticulture pages give the reason plainly. Plants are routinely tagged with hardiness zones higher than they actually hold, partly because nobody tested them in a cold enough winter. Buying colder than your zone is how you stop paying for that twice.

What the older streets already settled

Seventy years ago, by the City's own account, seven shade tree species could survive in Calgary, and four of them were poplars. The urban forest now runs to more than 70 varieties, and a poplar can stand for 150 years, which is why the older boulevards look the way they do. The species repeat because the alternatives died. The City still lists bur oak, Colorado spruce, Siberian larch, American elm and Manitoba maple among the trees that hold here, and it notes that bur oak withstands chinook conditions well.

The window that closes with the ground

Soil that has been warming since May roots a new tree faster than soil in April, and that advantage runs until freeze up. The University of Saskatchewan puts perennial division in late August or early September, about when the tree leaves are ready to drop, and names iris, lilies, lily of the valley, bleeding heart, peony and ajuga as the ones to lift and split. It also says to water deeply again about two weeks before freeze up, evergreens especially. The Calgary Horticultural Society says to keep watering trees until the first hard frost, typically late October here, and puts the growing season at around 115 days. Calgary soil runs alkaline at pH 7.5 to 8, so compost goes onto beds now for fertility next spring.

Bulbs in now, colour in May

Spring bulbs go in the ground in fall, and the Calgary Horticultural Society names its picks with the depths attached. Tulipa tarda sets 10 to 15 cm down and opens in May here. Muscari neglectum goes shallower, about 5 cm. Narcissus 'Minnow' plants in fall and blooms the following spring. Camassia leichtlinii blooms late in spring. Garlic follows the same logic on a stricter date, going in the first or second week of October, pointy end up and 10 to 15 cm down. Stop deadheading several weeks before the first killing frost, so the plants read the season and go dormant on time.

Chinooks, and what the schedule allows

The City describes a Calgary winter as extreme cold and dry chinook winds, sometimes arriving on the same day. Sun heats the bark through the afternoon and wakes the tree. The temperature drops the moment the sun goes, and what is left is sun scald, meaning elongated, sunken, dried and cracked patches of dead bark, usually on the south-facing side. Mulch over the roots insulates against the drying wind. October also opens the only window for elm work, since Alberta bans elm pruning from April 1 to September 30, while the bark beetles that carry Dutch elm disease are active and drawn to fresh cuts.

Watering runs on a year round schedule now, in effect since April 29 under the Water Utility Bylaw. Even street numbers take Tuesday, Thursday and Saturday, odd numbers Wednesday, Friday and Sunday, before 10 a.m. or after 7 p.m. A watering can or a spring-loaded nozzle is exempt any day, on anything except lawn and turfgrass. Newly planted trees and shrubs are exempt for their first five years, and sod for 21 days after it goes down.

The canopy is the part of a neighbourhood you cannot install, which is one of the things we read when we write up a Calgary neighbourhood. Every job above has a deadline set by the ground rather than the calendar. Dig a hole in November and you will find out where it is.