Upside-Down Patio Garden - When to Plant in Your Area

American Horticultural Society Plant Heat-Zone Map

The American Horticultural Society Plant Heat-Zone Map as shown below can help you to understand the types of temperatures to expect in your area, and how to coordinate planting and gardening for your area. To view larger version please Click Here or on the picture below.

If you are looking to find the heat zone specific to your location, you can use the American Horticultural Society's Heat Zone Finder which locates your heat zone via zip-code. Click Here to use this handy tool.

American Horticultural Society states you are to use the AHS Plant Heat-Zone Map the same way as a Hardiness Map. The 12 zones of the map indicate the average number of days per year a given region experiences "heat days"- temperatures over 86 degrees (30 degrees Celsius). That is the point at which plants begin suffering physiological damage from heat. The zones range from Zone 1 (less than one heat day) to Zone 12 (more than 210 heat days).

It is also important to know how to select plants based on the heat-zone for your area. Once you know your zone, it is best to consider the heat-zone range assigned to plants in order to help select appropriate plants for your region. An example from the American Horticultural Society is as follows: if I live in AHS Heat-Zone 7 and want to plant some petunias, I would look up the zone range for petunias and find they are heat tolerant throughout the range of zones within the United States (12-1); thus, I would know — based on heat tolerance — they are suitable for me to grow in my Heat Zone 7 garden.

Unfortunately some plants are not coded on their plant tags for their heat-zones, though more and more have them printed. With that in mind, there are reference books available which can answer most, if not all of your questions. Perhaps the most comprehensive single source for both heat and hardiness zone information is the AHS A-Z Encyclopedia of Garden Plants (2004 edition, published by DK publishing). Many other books have been published by AHS/DK. For a list, please visit the American Horticultural Society's Book page which can be accessed when you Click Here.

Reproduced with permission of the American Horticultural Society (www.ahs.org)