Timing of water application

The timing of irrigation is particularly important with vegetable crops if they are to develop steadily and produce the maximum yield. Care must be taken to give plants sufficient water. There must be enough to reach the roots, not just to wet the soil surface.

As a general rule, an inch of water will travel to a depth on 9 inches in the soil. To water an acre of land to this depth, a total of 22,650 gallons must be applied. Continuous light applications of water during periods or prolonged drought are not to the plants’ best advantage. They will not reach the majority of roots; they will pan the surface of the soil, and they will encourage the plants to produce surface roots. which will suffer in future droughts.

Sandy soils will dry out much more quickly than those containing clay, and will have to be watered sooner during spells of drought. The surface is seldom a good guide as to the state of the soil, so dig down for 9-12inches with a trowel to see if the soil is moist. If it is dry or only moist, water with a fine spray from a hosepipe or watering can.

With vegetable crops in particular the water can be utilised while the plants are growing rapidly – usually during late spring and early to mid-summer. Shortages of water at this time cause the greatest check and may even result in some crops bolting (prematurely running to seed).

Food crops

Later in the summer excessive quantities of water may do real harm to certain vegetables. Melons, for instance, should by kept on the dry side once their fruits are beginning to ripen, otherwise the fruits will split and be spoiled. Late summer rains or irrigation can impair the storage quantities of onions, just when they should be drying off prior to being strung. Beans and peas should be watered 1-2gal per square yard per week when the flowers and pods appear. Too much water during early growth encourages leaves at the expense of flowers and crops.

However, for most green crops such as lettuces, good supplies of water will keep them cropping, both prolonging and increasing their yields. A rate of 2-3gal per square yard per week is adequate.


Less research has been done on the water needs of ornamental plants. However, ornamental plants have much the same needs as food crops. Pot-grown flowers and shrubs are at greater risk than those in open ground. Do not let them dry out.

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