Shade cloth can help prolong growing season

By Angela O'Callaghan

Wednesday, June 3, 2009 | 5:13 p.m.

There is nothing like a lovely warm day in late spring, early summer, when everything green is just very green. This is not necessarily the situation every gardener wants.

Suddenly it is too hot for most tomatoes. In the desert southwest they needed to be established by the end of March. Fruit set needed to be started by early May. Once temperatures exceed 90 degrees, any new flowers that do appear will generally dry up and die without setting fruit. This is a survival mechanism – the plants produce fruit in order to get a new generation started. If it seems like the weather is too hot for seedling survival, then they are not going to waste all their limited resources, like water, sugar and protein. After all, creating fruits and the seeds within them is a very intense process for any plant. When the temperatures are very high, and especially when they are accompanied by low humidity, all they are going to do is continue to pull up water and produce lots of green leaves.

Fruits that have set will continue to grow and even ripen when it is that hot, but they can cook on the vine, not reaching full size or color if it gets much warmer.

This is not necessarily the whole story, however. It is possible to extend the season a little by offering a little shade to the growing plants. Easy to find in home stores and easy to cut to the desired size, shade cloth is one of the easiest ways to create a somewhat cooler haven. Tomato varieties that are particularly tolerant of high temperatures will benefit from this as well. Some varieties will soldier on despite desert heat and continue to produce into the low 90s. Unfortunately, even these cannot withstand a full Mojave summer.

Another member of the tomato family is pepper – red, green, yellow, bell or raging hot – all are cousins. While they needed to be planted and established just shortly after tomatoes, they have a higher heat tolerance than their more delicate relatives. (The same is true for eggplant, although they do have other problems.) Peppers will continue to produce viable flowers (which can develop into fruit) into the low 90s, although they would prefer it slightly cooler. For this reason, shade cloth will be a good addition to that part of the garden as well.

By the end of June or beginning of July, most tomato plants have started to look as if they have "passed". Then it will be time for the intrepid gardener to make a choice – either take them out and put them into the compost, or simply cut them back (nearly to the soil line), cover them with mulch (not rock) and keep the soil moist. Most likely they will produce new growth when the temperatures stay below 90 degrees. They are tender perennials and can be treated as if they were. This is not generally a good idea for other members of the family.

Angela O’Callaghan is the area specialist in social horticulture for the University of Nevada Cooperative Extension. She can be reached c/o the Home News, 2275 Corporate Circle, Third Floor, Henderson, NV 89074, or [email protected].