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Hot, Hot, Hot Garden - Page 5

© Marge Talt

I've found, through the process of trial and loss, that certain plants simply won't survive my torrid summer days and nights. Cornus canandensis is one such. I've watched it's painful demise as the weather heats up on several occasions. Delphiniums are another marvelous group of plants that despise my climate, as is the totally charming Alchemilla erythropoda and even more charming Alchemilla alpina. I've exceeded my three tries at killing both of these.

Heat Zone Map

Once again, The American Horticultural Society has come to the rescue. 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. Like the Hardiness Map, the US was divided into zones - twelve in all - indicating the average number of days in the year that the daily high temperatures reached or exceeded 86 F, the temperature at which plants begin to suffer.

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. Every issue of The American Gardener (the publication of the AHS) lists both the hardiness and heat coding for plants featured in the issue. 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.

So, start nagging your local nurseries and garden centers as well as your favorite mailorder nurseries to get with it and add the heat zone coding to their plant tags and descriptions!

Supplemental Watering

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. Water moves down much faster in sandy, coarse soils than in fine silt or clay soils, which is why clay and silt soils are called "retentive".

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. Frequent light waterings encourage plant roots to stay in the top layer of soil where they dry out faster as the soil dries.

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