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Rose Verhoeve - November 7, 2021

Plant Hardiness Zones

Hardiness Zones are geographical areas, defined by climate, to help determine what plants can survive, and grow well, in a particular region. The zones are defined by the region's lowest average temperatures, as well as snow depth, rainfall, wind gusts, and the highest average temperature. But when using the zones to choose a plant, they are defined by the lowest average winter temperature.

Click the image above for a better view.

Why is this important?

You want to make sure that you choose the appropriate plant for your garden. It’s also costly to choose plants that won’t survive the years to come.

What Zone am I in?

The Government of Canada has a page where you can find your plant hardiness zone by municipality.

What Zone is London, Ontario?

London, Ontario is actually split into zones 6a and 6b. To determine what zone you're in depends on where you live in London.

These are the zones minimum average winter temperatures:

6a: -23.3oC to -20.6oC
6b: -20.5oC to -17.8oC

Click here to determine which subzone you live in.

What are Hardiness Subzones?

The subzones are for the subclimates in each of the regions. The letter “a” means it’s a colder microclimate. If the letter is “b”, it means it’s a warmer microclimate. So for instance, Zone 6a is colder than Zone 6b. When you are shopping for perennials, the tag on the plant will say what zone it is but it won’t show the subclimate. That’s not a problem, just make sure you’re choosing the plants that can live in your zone.

Zones and Purchasing Perennials

If you are in the London region, your zone is 6. This means that you can buy any plant that has a hardiness zone below 6 and it will survive our winter climate. We recommend purchasing plants that are one zone below your regions zone in order to ensure survival and good growth. In this case, anything from zone 0-5 would be ideal for the London region. 

Most perennials sold in our greenhouse will have tags letting you know what zone they are. Make sure to double check the tag before purchasing anything to ensure that the perennial you're buying will have a long life in your garden. 


A temperennial is a perennial plant grown in a marginally temperate climate. Another definition can be "A perennial plant designed to live temporarily". Think of the two words put together to make Temperennial: Temporary and Perennial. A temperennial might live for 3 years and on the 4th year it dies. This means that a plant is not technically hardy to our zone and it would need a bit of extra care going into the fall and winter months. You can often guarantee overwintering of temperennials with proper protection.

The extra care could be:

-Planting it in an enclosed area.
-Heavily mulch the surrounding area.
-Plant it amongst other plants so they have their own microclimate.
-Plant it a maximum distance of 10 feet from the wall of your home in order for it to obtain some heat from the house.
-Wrap it with burlap.
-Leaf piles around the area.

Example of plants that are Temperennials:

-Ascot Rainbow Euphorbia
-Crepe Myrtle
-Callicarpa (Beautyberry)
-Musa Basjoo (Green Banana)