The best time to quench your plants' thirst is early in the morning, when plants are turgid and best able to take in more water; in fact, the morning dew that moistens the top few millimetres of soil makes it easier for water to penetrate deeply. Irrigating at midday is wasteful, as much of the moisture is lost to evaporation, while watering in the evening isn't ideal because leaves stay wet all night long, which can lead to disease.
Although traditional wisdom dictates that the average garden needs about 2.5 centimetres of water per week, variables such as soil type (for example, sandy soils dry out more quickly than clay), weather and the moisture requirements of individual plant species mean gardeners must tailor their watering to specific conditions. Specimens that look limp or wilted in the early morning or evening should be watered immediately-these are signs of stress and cellular collapse, a stage at which rehydration is difficult. Plants consistently deprived of moisture for too long will become more vulnerable to attack by disease and insect pests.
As a general rule, it's best to water less frequently but deeply; a light sprinkling will evaporate quickly and therefore fail to reach plant roots. (Test moisture depth by digging out a divot-15 centimetres or more is ideal.) A thorough watering also encourages plants to send their roots down into the soil where moisture is stored, rather than relying on surface water, which can be irregular.
The most efficient way to deliver moisture is by applying it at ground level. A porous soaker hose laid around the base of plants allows water to seep slowly down to the root zones without moisture loss due to evaporation or runoff. Once the hose is positioned, mulch can be added overtop to hide it and keep moisture from the evaporating rays of the sun. Drip irrigation systems are another option, but they are more costly to install and the tubes sometimes have a tendency to clog. For large gardens, it may be more practical to use overhead watering systems, with either in-ground or hose-end sprinklers.