Canada's plant hardiness zone map: making a good thing better!
First produced in 1967, the hardiness map is a visual tool that depicts geographic areas statistically associated with the survival of native and horticultural plants. In Canada, hardiness is not just about temperature. The Canadian hardiness zone system combines seven climate criteria: C minimum temperatures, maximum temperatures, frost free period, summer rainfall, snowfall, a wind factor and January rainfall, to delineate zones.
Canada now has a new map that retains the original hardiness system and builds upon it. Developed by scientists at Natural Resources Canada's Canadian Forest Service and Agriculture and Agri-food Canada, this "newer" tool employs cutting-edge topographic and statistical mapping techniques.
For the first time, the Canadian plant hardiness zone map incorporates the effect elevation has on climate and therefore, on plant survival. In order to include this critical feature, Canadian Forest Service scientists employed a computer-generated Digital Elevation Model of Canada, originally developed for forest research applications.
The amount of climate data available to statistically compute hardiness zones has more than doubled. The 1967 map used climate data recorded between 1930 and 1960. The new map keeps all the original data and adds climate measurements taken between 1961 and 1990. Comparing these two data sets has allowed researchers to identify changes to plant hardiness zone locations.
One other important change--the new map includes hardiness zone indications for all of Canada, not just the southern regions. Northern gardeners are now "on the map"!
How Have Hardiness Zones Changed?
From Manitoba westward, hardiness zones have generally increased, by about half a zone. This change suggests conditions have become slightly more "hospitable" for plants. In eastern Canada, hardiness zones appear generally to have declined by half a zone. Southern Vancouver Island and south-western Ontario show more dramatic declines.
Of course, the new map doesn't capture everything that affects plant survival. Canadian gardeners know from experience that well-placed microsite protection, either natural or created, can greatly increase survival of "borderline" selections in a garden or small-scale landscape.
Next Step: Plant-specific Hardiness Maps
Researchers at Natural Resources Canada, Canadian Forest Service are currently developing an Internet-based tool that will allow gardeners to identify the plants that survive in their locality. The ultimate aim is to develop climatic profiles for individual plant species. Once sufficient information has been acquired, range maps will be generated for viewing on-line.
Accessing the New Map:
The new interactive Canadian Hardiness Zone can be accessed on the Canadian Forest Service Web Site at ...
Those interested in `Going beyond the zones' to learn more about developing new plant hardiness maps can visit: http://g4.glfc.cfs.nrcan.gc.ca/ph_main.pl
The Plant Hardiness Zones map outlines the different zones in Canada where various types of trees, shrubs and flowers will most likely survive. It is based on the average climatic conditions of each area. The first such map for all of North America, released by the United States Department of Agriculture in 1960, was based only on minimum winter temperatures.
In 1967, Agriculture Canada scientists created a plant hardiness map for Canada using plant survival data and a wide range of climatic variables, including minimum winter temperatures, length of the frost-free period, summer rainfall, maximum temperatures, snow cover, January rainfall and maximum wind speed.
The new map
Natural Resources Canada's Canadian Forest Service scientists have now updated the plant hardiness zones using the same variables and more recent climate data (1961-90). They have used modern climate mapping techniques and incorporated the effect of elevation. The new map indicates that there have been changes in the hardiness zones that are generally consistent with what is known about climate change. These changes are most pronounced in western Canada.
Interpreting the new map
The new 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 most familiar to Canadian gardeners.
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 map. Year-to-year variations in weather and gardening techniques can also have a significant impact on plant survival in any particular location.
For more details and a close-up view of your local plant hardiness zone, visit the Canadian Forest Service page at: http://www.nrcan-rncan.gc.ca/cfs-scf/index_e.html or the Agriculture and Agri-Food Canada page at: http://sis.agr.gc.ca/cansis/nsdb/climate/hardiness/intro.html
Zone hardiness of some indicator trees 0b shining willow Salix lucida ssp. lucida 1 white spruce Picea glauca 1 lodgepole pine Pinus contorta var. latifolia 1 tamarack Larix laricina 1b laurel willow Salix pentandra 2 European white birch Betula pendula 2 white elm Ulmus americana 2a cranberry Viburnum trilobum 2b Manitoba maple Acer negundo 2b ponderosa pine Pinus ponderosa 2b Ohio buckeye Aesculus glabra 2b hackberry Celtis occidentalis 3 little-leaf linden Tilia cordata 3 Rocky Mountain juniper Juniperus scopulorum 3 red maple Acer rubrum 3b black walnut Juglans nigra 3b white ash Fraxinus americana 4 ginkgo/maidenhair tree Ginkgo biloba 4 black locust Robinia pseudoacacia 4a Rocky Mountain Douglas-fir Pseudotsuga menziesii var. glauca 4a sugar maple Acer saccharum 4b yellow-wood Cladrastis lutea 4b Scotch elm Ulmus glabra 5 Norway maple Acer platanoides 5 English oak Quercus robur 5a Douglas maple Acer glabrum var. douglasii 5b tulip-tree Liriodendron tulipifera 5b sycamore Platanus occidentalis 5b horsechestnut Aesculus hippocastanum 6 European beech Fagus sylvatica 6 tree-of-heaven Ailanthus altissima 6 redbud Cercis canadensis 6 goldenchain tree Laburnum X watereri 6 yellow-cedar Chamaecyparis nootkatensis 6 western redcedar Thuja plicata 6b eastern flowering dogwood Cornus florida 7 sweetgum Liquidambar styraciflua 7b Douglas-fir Pseudotsuga menziesii var. menziesii 7b Garry oak Quercus garryana 8 arbutus Arbutus menziesii 8 western flowering dogwood Cornus nuttallii 8 Monkey-puzzle Araucaria araucana Zone hardiness of some indicator shrubs 0 northern Labrador-tea Ledum decumbens 1 Saskatoon serviceberry Amelanchier alnifolia 1 hedge cotoneaster Cotoneaster lucidus 1 silver buffalo-berry Shepherdia argentea la Labrador-tea Ledum groenlandicum 2 Siberian pea-tree Caragana arborescens 2 Siberian dogwood Cornus alba `Sibirica' 2 European cotoneaster Cotoneaster integerrima 2 silverberry Elaeagnus commutata 2b common juniper Juniperus communis var. depressa 3 winged euonymus Euonymus alatus 3 staghorn sumac Rhus typhina 3 smooth sumac Rhus glabra 3a Canada yew Taxus canadensis 3b peegee hydrangea Hydrangea paniculata `Grandiflora' 4 bouquet blanc mock-orange Philadelphus `Bouquet Blanc' 4 Japanese yew Taxus cuspidata 4 black chokeberry Aronia melanocarpa 4a American hazel Corylus americana 5 common smoke-tree Cotinus coggygria 5 early forsythia Forsythia ovata 5 fragrant viburnum Viburnum carlesii 5a Oregon holly-grape Mahonia aquifolium 5b spicebush Lindera benzoin 6 Japanese maple Acer palmatum 6 slender deutzia Deutzia gracilis 6 showy forsythia Forsythia x intermedia `Spectabilis' 6 vine maple Acer circinatum 7 box tree Buxus sempervirens 7 Hidcote hypericum Hypericum hookerianum `Hidcote' 7 cherry-laurel Prunus laurocerasus 8 Japanese aucuba Aucuba japonica 8 Chilean pernettya Pernettya mucronata 8 laurestinus Viburnum tinus
The production of the new Plant Hardiness Zones map was made possible through a collaborative effort by scientists at Natural Resources Canada's Canadian Forest Service, Agriculture and Agri-Food Canada and Natural Resources Canada's National Atlas of Canada.