From: DK - Simple Steps to Success: Vegetable Gardening
Keeping Plants Healthy
Plants in dry soil are susceptible to disease and yield less, so it pays to keep soil moist. Watering thoroughly so the moisture penetrates deep into the soil is better than wetting the surface daily. Water in the evening or early morning to minimize evaporation.
Water can be collected from the roofs of houses, garages, sheds and greenhouses, and stored in rain barrels that have spigots at their bases. These supplies of rainwater are a valuable alternative to city water or well water, although during hot summer months, rainfall rarely keeps up with demand.
Rain barrels are often easier to install in a convenient part of the garden than running a hose to the area. Make sure that you set your rain barrel on a stack of bricks, slabs or a specially made base, to allow a watering can to fit under the spigot. Although many gardeners dislike the appearance of plastic barrels, they are easy to disguise with ornamental planting, such as grasses and bamboo (above), or tall rows of runner beans.
Using Gray Water
Water that has already been used in the home is usually suitable for watering plants in the garden. Normal household soaps and detergents do not damage plants, but avoid bleaches and strong disinfectants. Allow hot water to cool before applying it to the soil.
Water the Roots
Pour water around the stem base, beneath the plant's foliage, so that it is absorbed into the soil around the roots where it is needed. The shade of the foliage also helps to prevent evaporation, and neighboring weeds are not inadvertently watered, too.
Text copyright 2007 Royal Horticultural Society