Be aware of the hardiness zone in your area before you buy plants

If you are planning to buy a shrub, perennial or a tree, you need to make sure that this new plant will tolerate all-year-round temperatures in your area. To ensure that the new plant will survive and grow year after year you need to make sure that the hardiness zone in your area matches the hardness zone of the plant.

One would expect that local garden centres should only be selling plants that will thrive in local climate. This is not always the case. You need to remember that garden centres are in the business of selling their stock and what looks nice sells. That is why you need to do a bit of detective work before buying plants that look great in the nursery on a warm May day. Some plants may not survive over winter even though they look great in the nursery in the early spring at planting time. But what is hardiness zone? A hardness zone is a geographically defined area in which climatic conditions’ a specific category of plant life is capable of growing, including its ability to survive the minimum temperatures of winter.

Better garden centres list the hardiness zones as part of the description attached to the plants, but it is always prudent to double check the Canadian gardening reference books and nursery catalogues or just by searching the plant name online. Just make sure that you are using the Canadian reference sources as zones are differently defined for the U.S. and Canada. There are ten hardiness zones for the U.S. and only nine for Canada – that means that hardness zone 5 in the U.S. source refers to completely different climatic conditions that Canadian hardiness zone 5. Some of the plants you find in the nursery may be brought from the States and marked accordingly to the American system. All plants mentioned on our website refer to Canadian hardiness zones and each plant entry lists the range of zones where the plant is recommended.

In Canada, the Plant Hardiness Map produced most recently in 2000 by Natural Resources and Agriculture Canada scientists outlines nine different zones where various types of trees, shrubs and flowers will most likely survive. It is based on the average climatic conditions of each area, including minimum winter temperatures, length of the frost-free period, summer rainfall, maximum temperatures, snow cover, January rainfall and maximum wind speed. This updated plant hardiness map indicates that there have been changes in the hardiness zones consistent with the climate change. That may explain why some of the older plants in your garden do not perform well in the recent years. Also, one needs to be mindful that produced in 2000 hardiness map is already outdated. But this is still the best tool available to gardeners to help them to choose the best plants for their garden. The Canadian hardiness map is divided into nine major zones: the harshest is 0 and the mildest is 8. Relatively few plants are suited to zone 0. Subzones (e.g., 4a or 4b, 5a or 5b) are also noted in the map legend. These subzones are very important to Canadian gardeners, as they pinpoint to their garden location. You can also search for the hardiness zone by location, as well as use the interactive climate change forecasting tool to get a list of plants that will do well in your area in the future.

The hardiness zones differ even within the greater Toronto area, where Mississauga and Oakville fall into zone 6b (going up the scale from zone 6a in the late sixties when the first Canadian hardiness map was created), Brampton 6a (change from 5b) and Etobicoke 7a (change from 6a). That means that in most part of Mississauga only plants that survive in the lowest temperatures -20.6 to -17.8 C, should be planted, while this threshold is lower in some parts of Toronto, including Etobicoke, where this range is -17.8 to -15.0 C, and in Brampton where the range is lower between -23.3 and -20.6 C.

As every gardener learns, cold hardiness is only one factor in plant’s adaptation. Some significant local factors, such as micro-topography, amount of shelter and subtle local variations in snow cover, are too small to be captured on the hardiness map, yet they also influence the plant’s ability to survive. Other factors include the unique combinations of soil type, wind, rainfall, length and time of cold, humidity, summer temperatures, and temperatures in relation to humidity.

Another aspect of climate important in selecting plants is microclimate – the climate around your home that differs slightly from the general climate in your area. The northern side of your property, which is partially shaded most of the day by your house is cold microclimate. the southern part of your house, unless shaded by trees, receives hot sun almost all day, is a warm microclimate. At Landpol, when helping you plan your garden, we start with a site plan specific for your property. This helps us to identify the nuances in weather conditions and select the best plants for your garden.