Selecting Plants: Will That Plant Grow Here? The Reality of Zone Maps. - Page 3

When we look up the AHS Heat-Zone ratings for the six cold hardiness indicator plants listed above, we find that:

• Dogwood (Cornus florida)is suitable for zones 9 through 1
• Slender deutzia (Deutzia gracilis)for zones 8 through 4
• Early forsythia (Forsythia ovata)for zones 8 through 4
• Common privet (Ligustrum vulgare)for zones 9 through 1
• Boston ivy (Parthenocissus tricuspidata)is not rated, and
• Multiflora rose (Rosa multiflora)is suitable for zones 9 through 3.

Looking on the Plant Heat-Zone Map, I find my neighborhood region rated as a 4, with 14 to 30 "heat days." So, taking into consideration both cold and heat, all of these six plants except possibly Boston ivy should do very well for me.

There are two other plant hardiness maps that are in somewhat wide distribution: The Canadian Plant Hardiness Zone Map and the Sunset Climate Zone Map. The Canadian Plant Hardiness Zone Map was first introduced in 1967 based on Canadian plant survival data and a wide range of climate variables that included not only minimum winter temperatures, but also length of the frost-free period, summer rainfall, maximum temperatures, snow cover, January rainfall and maximum wind speed. The 2000 map, updated by the collaboration of several Canadian government scientific agencies, uses the same variables but incorporates recent climate data and the effects of elevation.

This map, with eight zones ranging from mild to harsh weather conditions, is very similar to the USDA map in interpretation and use. The Canadian map Internet site includes background on how the new map was devised, how to interpret it, a listing of indicator trees and shrubs, and an order form for a print copy.

Canadian zone 5 indicator plants which grow well in my yard include:

• Common smoke-tree (Cotinus coggygria)
• Early forsythia (Forsythia ovata)
• Fragrant viburnum (Viburnum carlesii)
• Oregon holly-grape (Mahonia aquifolium)
• Spicebush (Lindera benzoin)

• Japanese maple (Acer palmatum)
• Slender deutzia (Deutzia gracilis)
• Showy forsythia (Forsythia x intermedia'Spectabilis')

So I could consider my western New England yard as being a definite Canadian zone 5 and a marginal zone 6. I should not have problems relating when I read Canadian gardening publications or when I visit and consult nurseries in Canada.

The Sunset Climate Zone Map, introduced in the first Sunset Western Garden Book in 1954, has now been extended into a series of 23 regional maps based on factors which are important in determining climate: length of growing season, summer temperature highs, rainfall patterns and humidity, land formations and elevation, and nearness to oceans and other large bodies of water. These maps organize the United States and the southern part of Canada into 45 climate areas, and were developed with help from university climatologists, the National Weather Service, and agricultural extension agents across the United States.