Reducing Water Demands

Your garden soil may appear to have a high water content, but all water held in the soil may not be available to plants, particularly if the soil is heavy clay. Clay particles hold soil moisture tightly. If, for example, there are 4-1/2 inches of water per foot of this type of soil, there may be as little as 1 1/2 inches available for plants. The addition of organic matter is the first step in improving availability of moisture in the garden.

A relatively high level of humus in the soil, brought about by the addition and breakdown of organic matter, can increase the proportion of available soil water. Also, by causing clay particles to form aggregates or large groups of particles, humus adds air spaces to tight clays. Aggregation of soil particles allows excess moisture to drain to lower levels as a reserve, instead of puddling or running off and eroding the top layers of soil.

The moisture-holding capacity of sandy soils is also improved by additions of organic matter. Although most soil water in sandy soil is available, it drains so quickly that plants are often unable to reach water after even a few days following a rain. Humus in sandy soil gives the water something to cling to until it is needed by plants.

Mulching is a cultural practice which can significantly decrease the amount of water that must be added to the soil. A 6-8" organic mulch can reduce water needs by as much as one half by smothering weeds which take up and transpire moisture, and by reducing evaporation of moisture directly from the soil. Organic mulches themselves hold some water and increase the humidity level around the plant. Black plastic mulch also conserves moisture, but unless covered with organic material or foliage, it will increase soil temperature dramatically during the summer to the detriment of plants.

Shading and the use of windbreaks are other moisture-conserving techniques. Plants that wilt in very sunny areas can benefit from partial shade during the afternoon in summer. Small plants, in particular, should be protected or relocated.

Air moving across a plant carries away the moisture on the leaf surfaces causing more water to be needed by the plant. In very windy areas the roots often cannot keep up with leaf demands, and plants wilt. Temporary or permanent windbreaks can help tremendously.

During those times when cultural practices simply aren't enough, when rainfall is sparse, and the sun is hot, watering can benefit the garden with higher yields, or may save the garden altogether in severe drought years. Irrigation practices, when properly used, can conserve water. Drip and trickle irrigation systems use water more efficiently than overhead sprinklers. They deliver the water to the plants' roots where it is needed. For ease of operation, they can be connected to timers or water-regulating devices enabling them to be shut off automatically further conserving water when the demand for it is great.