Zone maps provide gardeners with plant hardiness information. Seasoned gardeners tend to get the nuances of zone hardiness and understand how their yard’s micro-climates might push a small, protected area into a warmer zone where they can over-winter an otherwise non-hardy plant. New gardeners likewise count on zone labeling but may not understand that a zone designation is only a guide, not a guarantee, of survival. Gardeners living near the edge of a zone may find current zone maps particularly confusing.
For example, my Connecticut location is zone 6 or zone 6a (indicating I live in a slightly chillier section of zone 6) according to 2006 or 1990 hardiness maps. Still, I know from experience that some plants listed hardy for zone 6 simply do not over-winter in my garden, though the same plants do well in other zone 6 gardens located just 5 or 6 miles away – but about 350 feet lower in elevation – and closer to the temperature-mediating Connecticut River.
New gardeners perusing seed and plant catalogues might notice slight differences in the zone demarcations they depict. Printing might account for some of the difference, but unless the catalog list which zone map it uses, one can never be sure. Many national gardening magazines additionally list the AHS heat zone map (my area is zone 4) to further clarify a plant, shrub, or tree’s heat tolerance. The best way for gardeners to sort all this out is to ask a seasoned gardener or professional for advice.
But the USDA may ultimately provide a more user-friendly plant hardiness zone map with the forthcoming release of its latest revision (see the Daily Climate article by fellow freelance writer, Jennifer Weeks). This updated map will offer localized zone information according to zip code … a feature I look forward to using. Still, I’ll continue to watch weather trends specific to my area and elevation, and mulch, mulch, mulch to ease even the hardiest plants through our unpredictable winter seasons. Zone maps offer good general guidance, but local observation, backed up by good solid journaling, remains an invaluable tool.