Gardening benefits the environment in myriad ways. Maintaining natural landscapes and preserving green spaces can reduce the collective carbon footprint of the human race. Trees, flowers and other greenery filter the air and create welcoming habitats for all species of animals and insects.
Many of us set out each spring to create landscapes that cater to all of the senses. But choosing plants that are unlikely to thrive in certain climates can lead to dissatisfaction and premature plant demise and may require gardeners to use more fertilizers, pesticides and other not-so-Earth-friendly techniques to help plants thrive.
One of the more important steps gardeners can take before spring arrives is to educate themselves about plant hardiness zones. Hardiness zones are defined by the average climatic conditions of the region and are broken down into various zones. The USDA Hardiness Zone map divides North America into 13 separate zones. Each zone is marked by 10 F incremental differences from the last zone. In some versions of the map, each zone is further divided into “a” and “b” regions.
The National Gardening Association says the USDA Hardiness Zone Map was revised in 2012. The latest version was jointly developed by the USDA’s Agricultural Research Service and Oregon State University’s PRISM Climate Group. To help develop the new map, the USDA and Oregon State University requested that horticultural and climatic experts review the zones in their geographic areas. As a result, the zone boundaries in the 2012 edition of the map have shifted in many areas.
Zone maps are tools that show where permanent landscape plants can adapt. Home gardeners who are looking for shrubs or perennials to last year after year should recognize that such plants must tolerate year-round conditions, including the lowest and highest temperatures and the amount of precipitation. Snow cover and humidity also can impact a plant’s propensity to thrive.
While zone maps are not perfect, they can be useful in planning and ensuring the survival of future gardens. Many other environmental factors, in addition to hardiness zones, contribute to the success or failure of plants. Wind, soil type, soil moisture, humidity, pollution, snow, and winter sunshine can greatly affect the survival of plants. The way plants are placed in the landscape, how they are planted, and their size and health might also influence their survival.
Arbor Day is April 27th! To find a list of suggested trees for your zone, visit arborday.org
A listing of woody plants under the coldest zones in which they normally succeed.
-10 to 0 F
-23.3 to -17.8 C
Buxus sempervirens (common boxwood)
Carya illinoinensis ‘Major’ (pecan cultivar – fruits in zone 6)
Cedrus atlantica (Atlas cedar)
Cercis chinensis (Chinese redbud)
Chamaecyparis lawsoniana (Lawson cypress – zone 6b)
Cytisus ×praecox (Warminster broom)
Hedera helix (English ivy)
Ilex opaca (American holly)
Ligustrum ovalifolium (California privet)
Nandina domestica (heavenly bamboo)
Prunus laurocerasus (cherry-laurel)
Sequoiadendron giganteum (giant sequoia)
Taxus baccata (English yew)
0 to 10 F C
-17.8 to -12.3 C
Acer macrophyllum (bigleaf maple)
Araucaria araucana (monkey puzzle – zone 7b)
Berberis darwinii (Darwin’s barberry)
Camellia sasanqua (sasanqua camellia)
Cedrus deodara (deodar cedar)
Cistus laurifolius (laurel rockrose)
Cunninghamia lanceolata (cunninghamia)
Elaeagnus pungens (thorny elaeagnus)
Ilex aquifolium (English holly)
Lagerstroemia indica (crapemyrtle)
Melia azedarach (chinaberry – zone 7b)
Osmanthus heterophyllus (holly osmanthus)
Pinus radiata (Monterey pine – zone 7b)
Rhododendron Kurume Group (Kurume azalea)
Sequoia sempervirens (coast redwood)