The most important cultural practice for a healthy and productive home vegetable garden is irrigation. During years of normal rainfall (12 inches or more), winter rains usually wet the soil to 6 feet, getting us off to a good start with a supply of deep soil moisture. What happens later on will depend upon your watering skills, and the efficiency of your irrigation system.

Once the growing season is underway, vary the amount and frequency of irrigations according to the rooting depths of the vegetables you grow. Shallow-rooted crops, including lettuce, sweet corn and radish, have most of their roots in the top 12 inches or so of soil. Moderately deep-rooted crops are those that have most of their roots in the top 24 inches of soil, and include snap bean, carrot, cucumber, eggplant, pepper and squash. Deep-rooted crops are those where the main root system is in the top 36 inches of soil, and include cantaloupe, pumpkin, tomato and watermelon.

Remember that clay soils hold more usable water (water which plant roots can extract from the soil) than do sandy ones. In a sandy soil, each foot of depth usually holds 3/4 inch of usable water. The same depth of clay soil holds 2 to 21/2 inches of water. For this reason, you don't need to irrigate a clay soil as often as a sandy one.

You will probably need to water you vegetable garden one or two times a week in summer, depending on crop, soil type and the temperature. Wet the soil to a depth of at least 24 inches at each watering. If you only keep the surface of the soil moist, most of the water evaporates to the air and is lost to the roots, which are deeper than the top 3 or 4 inches of the soil.

There are a couple of measurements you can make to assure that you are applying adequate water. If you use a garden hose, turn it on to the force you commonly use and time it to find out how many minutes it takes to fill a one-gallon can. This gives you the rate of water flow per minute. In general, one gallon of water will wet 1 square foot of ground to a depth of 1-1/2 inches.

If you use a sprinkler system, place some empty cans under the sprinkler spray at various spots. Keep track of the length of time the sprinklers are on and then measure the depth of the water in the cans when you turn off the water. Average the various depths to determine how much water is being applied to the garden at each sprinkling.

Drip irrigation offers several advantages to home gardeners. You can place water more slowly and accurately in the root zone, with little or no water waste. Also, the furrows remain dry, so you can work in the garden while irrigation is in progress; dry furrows also means less weed growth. The disadvantages are the added costs of the drip irrigation equipment and occasional problems of plugging of the tiny drip orifices. But the advantages outweigh the disadvantages, and a drip irrigation system, when correctly installed and maintained, can be used very efficiently.

Soaker hoses are a form of drip irrigation and are useful if your rows are short (20 to 25 feet) and the soil is level. For longer rows, or on sloping ground, soaker hoses do not provide as uniform an irrigation as that provided by a true drip system.