Heat Zones

Heat can be as crippling to plants as cold. Plants that can't handle heat have to work too hard to keep their processes running. They may stop blooming, leaves may droop and turn pale, blue-gray or brown. The heat may not kill them outright, but it puts them under so much stress that they're more likely to be preyed upon by pests and disease.

When you're researching plants you want to add to your garden, try to determine not only their cold-hardiness but their sensitivity to heat. Descriptions typically include phrases such as "provide afternoon shade in the South." Catalogs and some plant labels carry the AHS Heat-Zone rating. Developed by the American Horticultural Society, the Heat-Zone map divides the country into 12 zones based on the average number of days per year the temperature is warmer than 86 degrees. Zone 1 — the most northern zone — has less than one such day; Zone 12 has more than 210. The rating is usually listed after the cold-hardiness zone rating.

To find out your heat zone, consult the American Horticultural Society's Heat-Zone Map.