Heat zone map

The cities of Portland, Oregon and San Antonio, Texas - both great places to visit, live and garden - are listed as zone 8 on the USDA's hardiness map. Summer growing conditions, though, are vastly different. Recognizing that summer heat also can have a devastating effect on the life-or-death struggles of many plants, the American Horticultural Society has developed a new map establishing guidelines for heat tolerance that gardeners can use to select the best plants for their climates. The map shows 12 different zones for the U.S. and Canada, each representing a temp range. Each zone is defined by average annual days above 86 degrees Fahrenheit (30 degrees Celsius) as determined from the records from 1974 to 1995. (Eighty-six degrees is the point at which plants suffer damage to cellular proteins.) Other factors, such as humidity, elevation, wind, proximity to large bodies of water also figure in the calculations. Thus, much of Oregon is heat zone 4 (14 to 30 days above 86 degrees) while south central Texas including SanAntonio is heat zone 9 (120 to 150 days above 86 degrees.) Another example: southernKansas and southern Pennsylvania are both hardiness zone 5 but heat zones are 8 (90-120 days) and 4 (14-30) respectively.
As nurseries and seed companies begin to reflect this information for the public, gardeners will have a valuable tool in assessing the chances for survival of any given plant in their locale. Thus far, the wholesale nursery Monrovia is including this information on their plant tags.

For a time, the American Horticultural Society was also showing the draft of the next expected revision of USDA's hardiness map, but is not currently doing so as the target date for publication has not been announced. Using refined meteorlogical data, the new map is expected to have 15 zones,reflecting the increasing adaptability of subtropical varieties. Yuska ( USDA zone 8b, heat zone 9)

The new Southern Living Garden Book has this in it. My area is in Zone 9.

Here's a link to a heat zone map.
http://www.ahs.org/pdfs/heatmap.pdf
Probably just gossip, but I read somewhere that the delay in the release of the heatzone map is because the zones are creeping due to global warming, and it's supposed to be a secret...;>) It must be true, I read it on the internet!
Natasha

Thanks for the info about Southern Living Garden Book, konkreteblond. I'll make a point to order it. I'm currently reading the book "Heat Zone Gardening" by Dr. H. Marc Cathey, president emeritus of AHS. As he explains, the death of plants from heat is more subtle and slower than from freezing. Sometimes the plant will struggle through a couple of seasons before finally succumbing. As a gardener prone to experimentation, I have often tried growing plants that are marginal for the climate. I find that I have a better chance of bringing a tropical plant such as tree spinach (chayamansa) through the winter than getting a cool-climate favorite such as a medlar tree to grow. I planted a young medlar three years ago and it has not grown at all, and I really doubt that it will leaf out at all next spring. Natasha, the heatzone map has been published and released; it is the revised USDA hardiness map that is delayed. An e-mail from David Ellis of AHS advises that the USDA decided to rework the 2003 draft without asking AHS for help, so the current status of the project is unknown. Certainly climatic changes of any type will affect plant performance to some degree. Tools such as the heatzone map will be ever more useful in achieving good gardening results.
Yuska

I've just been gardening for about 4 years now, and I've figure out that not all plants can take this TX heat. If it says "full sun", it might not understand what our "FULL SUN" is. What that means for me is lots of watering.

And along with "full sun" go the factors of humidity and wind. A lack of moisture in the air accompanied by even a moderate breeze will tend to pull moisture from the tissues of the plant. The plant then calls for water reserves from its roots and surrounding soil. We can help stabilize moisture movement by good mulching techniques. Yuska