The sudden change from cool to hot weather leads me to believe that we may really have a summer this year. If you haven't done so yet, it's time to begin a watering program for your home fruit and nut trees. Home orchard trees began growing with a excellent supply of soil moisture this year, and you don't want to lose the advantage by allowing the soil to dry out before applying irrigation water.

Fruit trees grow and produce best if you irrigate them deeply several times a season, but the amount you need to use varies with the size of the tree. Newly planted trees require less water than mature trees, but young trees need to be irrigated more often. Newly planted trees that are inadequately watered usually stop growing and remain stunted the rest of the season. One of the most important reasons for carefully irrigating young trees is to develop a deep and extensive root system early on. Fruit trees with shallow, poorly developed root systems usually remain permanently stunted. Mature trees need more water because of their greater size and leaf area, and because they have a larger crop of fruit to maintain. If you allow your trees to dry out and stop growing they will produce small, poor quality fruit, their bark will sunburn, and they may be attacked by borers.

It's important to learn how much water is needed to wet the soil as deeply as the roots can grow. Merely sprinkling the soil surface does no good. The day after you water, dig a hole with a shovel or an auger to see if the soil is wet in the entire root zone. For most fruit trees, the soil should be wet two to three feet deep.

Water requirements also vary with soil type and depth. In general, trees growing on sandy soils require more frequent irrigation because these soils do not retain moisture well. Clay soils need less frequent irrigations, but larger amounts of water need to be applied to wet the soil deeply.

As a general rule, you'll need to water trees growing in a sandy soil every 10 to 15 days. Water trees on a clay loam soil every 15 to 20 days. Use the shorter intervals during the hot days of summer, and the longer intervals in spring and fall when the weather is cooler. Trees growing on shallow soils should be watered more often than those on deep soils.

Most of the roots that absorb water and nutrients are out as far as the ends of the branches (the dripline), and usually much further. Therefore, you need to apply water in this area, away from the base of the tree. A good system is to make a basin under the tree and fill it with water every 10 to 20 days, depending on soil type and weather. The basin should be 3 to 6 inches deep and extend from the dripline nearly to the trunk. Keep water from 12 to 18 inches away from the trunk, because soil borne fungus diseases such as crown rot are encouraged by keeping the soil too wet near the trunk.

Home fruit and nut trees are often planted in lawns, which often results in many health problems for the trees. The irrigation system is almost always designed for the lawn, applying water on a frequent and fairly shallow (6 inches deep) basis. This is just opposite of what fruit and nut trees need for best growth and production. Soil-borne crown and root rotting diseases often kill home orchard trees in lawns, because the diseases thrive in wet soils. If possible, always plant fruit and nut trees in your garden where you can give them the irrigation and other special care they need.