Landscape Irrigation

Most of the country is now under the influence of the hottest part of the year - even here in normally cooler north Idaho, temperatures have risen into the nineties for over a week. To keep your gardens thriving in these conditions is a challenge, and requires the careful management of irrigation practices.

The following tips will help set you up for a successful irrigation project:

Studies have indicated that plants utilize root zone water most efficiently during morning hours...try to irrigate very early in the day. Much of the water applied during the heat of the day is lost to evaporation - thirty percent or more is lost from overhead irrigation. Watering during the evening or nighttime hours may be acceptable, but plants that are susceptible to fungus diseases will suffer from being damp for an extended overnight period.

The general rule is to water as deeply and as infrequently as possible. Watering deeply and infrequently encourages the plant to develop a deep root system, which in turn increases drought hardiness since the soil dries from the top down. Frequent, light irrigation encourages a shallow root system that will suffer from every dry spell.

Many folks have asked how much, or how long to irrigate...this depends on the soil - and the crop. In an "average" loam, one inch of irrigation will penetrate twelve inches...in sandy soil, penetration will be deeper, and in clay soil, not as deep. For established shrubs in the average loam, thorough, deep irrigation once per week to the depth of one and one half to two feet should be adequate during the growing season. Since clay soils hold water longer, care must be taken to not overwater, which will exclude necessary oxygen from the soil profile.

(The "ideal" soil is composed of fifty percent solids, twenty-five percent liquid, and twenty-five percent air).

Plants have different water needs...for instance, the red-twig dogwood (Cornus stolonifera) will thrive in a soil that is always damp - but many other plants require a thorough drying between irrigations - so if at all possible, group plants of similar water needs together. The website review below refers to an excellent article about designing for efficient water use.

For lawns, there is no substitute for overhead irrigation. For shrub beds, vegetable and herb gardens, and fruit trees, drip irrigation is far superior - the plants receive a slow, metered supply of water, which is not as susceptible to losses from evaporation and overspray. For row crops in the vegetable garden, I've been using "porous pipe," made from recycled rubber, with great success.

As with most topics relating to the garden and landscape, irrigation solutions are dependent on site-specific conditions - you must know your soil and your plant needs to make the best irrigation decisions.