Spring not the kindest time for vegetables

By Angela O'Callaghan

Wednesday, March 18, 2009 | 6:57 p.m.

Here in Southern Nevada, spring means that nighttime temperatures are reaching the point where the seedlings of garden plants can be placed outdoors. Spring is, sadly, perhaps our shortest season. One of the big problems that any Mojave gardener faces is the span between high and low temperatures that can occur within a single day. A 30-degree spread is not all that unusual, and most of the plants we grow for vegetables do not enjoy those kinds of extremes.

It is fortunate that lettuce, spinach and other things we grow for their leaves have been growing ever since night temperatures began exceeding 40 degrees several weeks ago. In just a few weeks, however, it will be so hot that many of these cool season crops will start to "bolt" — producing a flower stalk and becoming inedible. After mid-April, it makes sense to stop bothering with these plants, and resume growing them after mid September.

The opposite problem occurs with the prima donnas of the garden. Tomatoes, peppers, melons and the like will revolt when placed outdoors before it is considerably warmer than the ideal temperatures for leafy vegetables. Tomatoes, which everyone wants in abundance, can be the fussiest. If the intrepid gardener places them outside when it is below 50 degrees, they can suffer from what is known as "chilling injury." At the other extreme, when temperatures are much above about 85 degrees, the plants can stop growing, producing neither flowers nor fruits. This results in a fairly narrow window for tomato success, which is why we start seeds indoors under lights and plant seedlings, not seeds, outdoors. This is also one of the reasons we recommend growing smaller tomatoes, since they generally require fewer days to produce a ripe fruit.

The other warm season plants — peppers, okra and melons — react even more poorly when night temperatures are below 50 degrees. They actually do better closer to 60 degrees. On the other hand, they too will respond poorly as we approach our peak Mojave summer heat, although they will often continue to grow well into the 90s. There is no solid research on whether very hot peppers, such as habanero or jalapeno, survive very high temperatures better than ordinary bell peppers, although it is tempting to think that they could. If anyone has information on this, I would enjoy hearing about it.

Growing prima donnas in pots can be the easiest way to accomplish the task of keeping them alive and getting a reasonable crop. The same guidelines hold true for tomatoes, peppers and other warm season plants. A large plant will require about a five-gallon pot filled with a highly fertile mix or soil. Protect it from the brightest, hottest afternoon sun. Keep the soil moist but not wet. Do not fertilize with a high nitrogen fertilizer (the first number on a fertilizer package) after the plant is well established. Rather, use a product with a higher second and third number (phosphorus for flowers and potassium for water balance.)

By May, the plant should be flowering and beginning to produce a crop that can continue until July.

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, 2360 Corporate Circle, Third Floor, Henderson, NV 89074, or [email protected].