How to use plant hardiness zones to figure out what seedlings you can grow.

Not all seedlings can survive Canadian winters. Before you start your planting project, you need to understand how plant hardiness zones affect what you should plant.

getting ready to plant a spruce seedling
Getting ready to plant a spruce seedling.

What is a plant hardiness zone?

Some growers have never heard of the term “hardiness zone”. Even if they have, they do not realize what it means. So what does it mean? Hardiness zone refers to a region’s climate as it relates to plant growth and survival.

In North America there’e two primary guides, the USDA and the Canadian. The USDA is based on minimum temperatures. Whereas the most recent Canadian update includes minimum temperatures, rainfall, and frost-free days. The systems are about half zone apart. So they are similar, but not identical.

In Canada, we break our geography down into nine hardiness zones: with the harshest being 0 and the mildest being 8. We further subdivide each zone into a or b subzones. These zones help guide you with your seedling selections and should be a primary consideration.

Plant Hardiness Zones Canada
Plant Hardiness Zones Canada. Source Natural Resources Canada.

How does the plant hardiness zone affect your seedling?

All seedlings have a hardiness zone ideal for them. This is where they can survive and thrive best. Temperature decides your seedling’s zone. As mentioned earlier, your zone should be a primary consideration when preparing your selections. Your zone may be too hot or cold for your pick. This causes your seedling to fail or even die. Take a Tamarack, for example. Tamaracks are cold-hardy trees that thrive in northern Canada. A Tamarack seedling will not survive in Arizona due to the extreme heat.

Siberian Larch plant hardiness zones
Siberian Larch in the fall

How do I determine my zone and seedlings?

Natural Resources Canada has an interactive map to help you determine your zone. First, locate your region on the map. Next match your region’s colour with the legend. Yes, it’s that simple.

Now you need to find the right seedlings for your zone. Most commercial growers can give you that information. Or you can look it up online. TreeTime.ca lists hardiness zones on the right-hand side in a seedling’s quick facts section. We also have a plant finder that will recommend seedlings.

TreeTime.ca Plant Finder
TreeTime.ca Plant Finder

Can I plant seedlings outside of their zone?

Let’s say you live in Fort McMurray, a 3a zone and you want to plant Ginkgo Biloba, a 4a zone. Does this mean you cannot plant Ginkgo? The answer is no. Hardiness zones are a guide. It is OK to make an exception. Most seedlings have a zone rating to determine their ideal growing zone. This doesn’t mean you can’t plant outside a seedling’s zone. If you don’t mind a bit of risk, try it if only for the thrill of growing something that ordinarily wouldn’t exist in your zone.

Or you can play it safe, plant a Blue Spruce and watch as your neighbour claims bragging rights to the most beautiful tree in town. For more information on seedling planting, check out our Planting Site Selection & Preparation post.