Extension Service Garden Hints

Some vegetable crops are more water-wise than others

CORVALLIS, Ore. - Most gardeners these days get lots of advice about how to save water with water-wise gardening techniques. One approach is to plant crops that require less water in the first place.

"Some vegetables are adapted to drought conditions at a very basic, cellular level," explained Jim Myers, professor of horticulture at Oregon State University. "Some beans have this characteristic. Tepary beans (a close relative of common bean), for example, are grown successfully in desert and near desert conditions. The tepary bean is native to the American Southwest and has been a staple food crop in that area for at least hundreds and probably thousands of years."

Beans in the cowpea group (Vigna unguiculata) also have this characteristic. The familiar black-eyed pea is one of these. It not only doesn't need much water, it grows poorly if it's watered too much. The vegetable counterpart of the cowpea is the yard-long or asparagus bean.

Other vegetables cope with dry conditions using various avoidance strategies. Some common beans, like snap beans and pole beans, for instance require only a relatively short growing season and can set a crop on residual moisture.

Tomatoes, squashes and melons establish deep root systems quickly and are able to draw moisture from the deeper soil long after the surface has become dry in midsummer.

"As long as these crops have water early in their growing season, they're tolerant to terminal drought," said Myers. "In fact, many tomatoes actually do better if you cut off irrigation in mid- to late summer."

Okra withstands drought well, he says. It doesn't produce as well in northern states because it needs longer nights; but if you start it early in the season in a greenhouse and transplant it, it will bear.

One of the difficulties in choosing drought tolerant crops, such as okra, is that they are often adapted to a warmer climate than typically found in Oregon, and do not do well when we try to grow them here.

By and large, cool-season crops are not drought-resistant. Many of them originated in the Mediterranean region, where they germinate in the fall rains, grow slowly through the mild but cool winter, and flower and fruit in the spring. These are the cool-season legumes like peas, lentils and faba beans, and the crucifer crops, including Brussels sprouts, cabbage, cauliflower, collards, kale, kohlrabi, mustard, broccoli, turnips and watercress. If you plant them in the spring to grow through our hot dry summer, don't expect them to do it without extra water.

Sweet corn and lettuce are shallow-rooted and have high water use requirements. Sweet corn does not do well under drought conditions and may not develop an ear at all if conditions are severe.

As a rule of thumb, warm season crops will do with less water than cool season ones, and crops with deeper root systems will be more drought resistant than shallow rooted crops.

Within any crop some varieties are more drought-resistant than others, says Myers. Unfortunately, this information isn't easy to come by. Although researchers at the OSU Extension Service make lots of information available to the home gardener, so far a list of vegetable varieties sorted by drought-tolerance hasn't been developed.

In addition to using well-known water-wise techniques like drip irrigation and mulching, try grouping your vegetables according to their water needs when you plant them. That way you can vary the amount of water you give different parts of your garden. And in general, try giving your crops no more water than they need – rather than as much as they can withstand.

By: Davi Richards
Source: Jim Myers

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