How to - Gardening Basics

Hardiness zones demystified

Katharine Fletcher

What do those zone numbers mean... and how do they apply to my garden?

A micro-climate example
Over time, gardeners may recognize the subtleties of micro-variations in their gardens. Let’s look at an example. My farm, Spiritwood, is near Ottawa, but on the northern, more elevated (read: exposed, harsher) Quebec side of the Ottawa River. Whereas Ottawa is in hardiness zone 5a, according to the zone map, my farm, located 50 minutes northwest of the Parliament Buildings, is between zone 4a and 4b.

Interestingly, my growing season is different than that of some friends who live a 20- to 40-minute drive west of me, in harsher conditions. While my tomatoes ripen on the vine; theirs frequently must be gathered to ripen indoors.

Moreover, because of microclimates my husband Eric and I have created since 1989, we can extend our plant hardiness zone to (somewhat unreliably) include species requiring 5a.

Beyond the zones
Natural Resources Canada’s Canadian Forest Service is now calling on the public to tell them which plants from a comprehensive list are surviving in their zone. These will be added to range maps for individual trees, shrubs and perennial flowers. Take a look at the website to discover how you could contribute data for this project.

Katharine and Eric Fletcher are keen gardeners. They live on a 100-acre farm, Spiritwood, northwest of Ottawa, where they enjoy their organic vegetable and perennial gardens. Follow Katharine @Spiritwood.

Main image by Mike Rodriguez/iStock


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