A horticulturist with many years of field experience once remarked to me that if gardening problems related to water could be eliminated, we would have over 90 percent fewer gardening problems. It's no doubt that irrigation and irrigation-related problems result in poor growth or death of many garden plants, especially when the weather is hot for several weeks. How well you are able to avoid such problems depends upon your knowledge of your soil and plants.

One way to decide when to water is to carefully watch your plants. Although symptoms vary from species to species, you should be able to tell when your plants are running out of water. The leaves of many plants, like turfgrasses, turn a dark bluish-green color or wilt. Plants with large succulent leaves, like squash and cucumbers, may wilt during the hottest part of the day, then recover in the evening as temperatures drop. This temporary wilting doesn't necessarily mean the soil is dry. The plants may simply be transpiring water more rapidly than the roots are absorbing moisture. If the plants are still wilted in the evening, or wilt early in the day, they definitely need watering.

Woody plants, like landscape trees and shrubs, usually don't show water stress as readily as annuals or herbaceous plants. Symptoms on woody plants may include yellow leaves, "burning" on the edges of leaves, reduced shoot growth and smaller leaves, wilting and drying leaves and finally dying branches. Conifers such as cedars and pines often die from the top down. By the time you see leaf drop and dieback symptoms, the trees have been seriously drought stressed.

Both woody and herbaceous plants are injured or killed by overwatering as often as by underwatering. Symptoms of plants growing in water saturated soil include yellow leaves, gradual defoliation and eventually death of branches. The yellow leaves often closely resemble deficiencies of certain nutrients, like iron or nitrogen. Plants that are being overwatered are often killed by soil borne root and crown rotting fungus diseases. Such root killing fungi as Pythium spp. and Phytopthora spp. are especially troublesome in landscapes where irrigation water is being applied several times a week.

Since woody plants are often stressed before drought symptoms show up, you should actually check the soil around trees and shrubs, You cannot tell how wet or dry a soil is by looking at the surface, so dig down and remove a soil sample. Try to roll or squeeze it into a ball. If the soil will not form into a ball, it's probably too dry to supply water to plants. If the soil forms a ball, rub it with your thumb. If the ball will not crumble, the soil is wet enough. Very sandy soils are the exception, since they will crumble even when wet.

You can get an idea of moisture conditions throughout the rooting area by sampling the soil in several locations and from several depths at each location. lawns and leafy vegetables root mainly in the upper 6 inches of soil; tomatoes and small shrubs root mainly in the top 18 to 24 inches of soil; large shrubs and trees root mainly in the top 2 feet of soil, with some roots penetrating to 3 feet. When checking the soil beneath large shade trees, be sure to begin beneath the outermost branches (dripline). The root systems of many common shade trees may extend up to three times the diameter of the dripline, so that is where you need to dig. A soil auger is a good tool to obtain the deeper samples, but a shovel also works well. Be sure to sample different spots each time.

As you gain experience by checking your soil and observing plant symptoms, you'll become better able to water your garden properly. Remember to be more observant during hot, windy weather, as plants use water faster during those conditions.