In 1997 they published this Heat Zone map from data archives of the National Climatic Data Center, compiled by Meteorological Evaluation Services Co. Inc., who analyzed daily high temperatures recorded between 1974 and 1995 by the National Weather Service. Dr. H. Marc Cathey, AHS President Emeritus, the moving force behind both the Hardiness Map update and the Heat Zone Map, has been working hard assigning heat zone codes to plants, so far coding more than 20,000 of them. Monrovia Nurseries, who helped underwrite the map, have begun putting heat zone coding on their plant tags, and others will follow suit as time passes. Until this coding is as universal as hardiness zone coding, however, it will be difficult for gardeners to make practical use of the information. If we garden in climates that normally provide adequate rainfall, we must resign ourselves to providing additional water in times of drought - if we are able to.
Water seeps down through the soil gradually.
Each soil layer must be filled to capacity before water descends to the next layer. A certain amount of water is needed by plants for healthy growth. If only half that amount is supplied at a given time, it only penetrates the top half of the soil at the root zone. The area below this will be just as dry as if no water had been supplied at all. That's why it's important to water deeply when you water.