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Understanding growing zones

Gardeners can be conservative or adventurous, traditional or daring. The conservative or traditional gardener chooses plants they know will grow well in their garden. They depend on these plants for a successful garden year after year. The adventurous or daring gardener wants to push the limits and grow plants that are not commonly found in their area. For these gardeners success (and failure) is part of the fun of gardening. Both types of gardeners can benefit from understanding zone maps and hardiness ratings when choosing perennials that fulfil their garden aspirations and annuals that add seasonal colour.

Hardiness zones or ratings are listed in gardening magazines, reference books, plant catalogues and on seed packets. Each zone is determined by a 12.2 C (10 F) difference in the average minimum temperature. Zone 1 is the coldest and Zone 11 has the warmest winter temperatures.

A plant listed as hardy in Zone 4 indicates it should survive winter temperatures as low as -34.4 C (-30 F). A Zone 9 plant is hardy only to -6.6 C (20 F). Some references provide a range of zones in which the plant will grow. A plant listed as hardy in Zones 4 to 9 means it will grow in all of those zones. However, there are many factors that affect a plant’s ability to grow in a particular climate including exposure, altitude, moisture, soil type and even snow cover. These conditions create variations between and within zones.

While it’s unlikely that a plant listed as hardy in Zone 7 would survive in Zone 4, you may be able to grow plants recommended for warmer zones. Your garden may have a microclimate that’s not typical of the actual zone where you live. Variations in temperature, moisture, soil and light can be used to place plants where they have the best chance of growing. Trees and buildings provide shade and protection from strong winds, while south-facing fences and walls absorb heat to create a warmer microclimate.

You may be able give plants special attention to help them survive out of their recommended zone. The garden could be in a protected location, grow plants in a warm south-facing garden and make sure plants are covered with mulch or snow during the winter. Another option is to move plants into an unheated garage or another protected location that doesn’t get as cold as the outdoor temperature. Some gardeners may also move tender plants indoors during the winter months.

Your local garden centre will be able to help you identify your zone information.

No matter what type of gardener you are, your choice in plants may seem almost endless. Knowing about hardiness zones can help you make the right selections for your garden. †

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