Plant life is intimately bound to water. Air is equally vital in the soil as well as, of course, above ground. In fact, these two are partners; they operate harmoniously in the soil to the advantage of plants growing therein. But water-or rather, the lack of it-is generally more troublesome.
No part of the United States, whether fog-shrouded islands off the coast of Maine, a Midwestern prairie or a seashore spot in California, has escaped periods of drought during which not enough rain fell to maintain plant life. Most sections of the country can expect droughts like this about one year in four.
More often than not, water needs of plants are not considered until cultivation, fertilization and other contributions to growth have been provided. Watering is frequently given no thought until heavy rains of spring and early summer have evaporated and growth begins to show signs of suffering for water. However, if full advantage is to be taken of time, effort and money expended to build up Gardener's Loam, provision for a reliable water supply should receive attention in the initial garden planning.
A BASIC FOOD
Above all, water is a food. Less than 2 per cent of plant tissues are composed of minerals absorbed from soil elements; roughly 98 per cent of the tissues come from air and water. Even the 2 per cent from soil can enter and move through plants only in soluble form. It has been estimated that to produce a single pound of dry matter requires absorption, use and evaporation of at least 700 pounds of water. Of this, less than 1 per cent is retained in plant tissues, either as moisture or as elaborated food. During a single day, a mature tomato plant gives off as much as a gallon of water, while an acre of hay during a single growing season may transpire as much as 700 tons of water.
All this water is derived from soil except for the little absorbed through foliage from dew and rains. Consider where this soil water must come from. In humid parts of the country, it accumulates from snows in winter and heavy rains in spring, with a somewhat smaller accumulation from summer and fall rains. During dry periods, some gardeners may have to add as much as 10 per cent of a season's water supply from city mains or wells. Many gardeners never water at all. In dry districts as much as 100 per cent of the total water needs of plants must be supplied by irrigation. This does not mean that in humid climates artificial watering should be neglected.