Water Conservation in the Landscape

Selecting plants that naturally use less water is the first step in water conservation. Plants have many different strategies for using water. Some plants, like black walnut, are water spenders. They have an extensive root system that can explore lots of soil. As long as some of the roots are in moist soil, they can survive drought. However, they still use large amounts of water. Other plants, such as bermuda grass, are drought evaders. When it becomes too dry, bermuda grass just becomes dormant. Finally, there are water conservers. These plants have ways to reduce water loss. Manzanita has leaves with a vertical orientation which reduces solar radiation and thus transpiration. Water loss from plant leaves is called transpiration. Oaks have leaf surface hairs that reduce air movement across leaves. Other plant adaptations include small leaves, grey color, and leathery leaves.

There are several things you can do for more efficient watering. First, apply two to four inches of mulch under the plant canopy. Mulch is one of the best ways to maintain soil moisture within the zone of actively growing roots. It can consist of pine needles, leaves, bark, wood chips, straw, compost, or any other organic materials. Mulch should be kept from direct contact with the trunk and should be extended as the plant grows.

Second, follow good irrigation practices. Avoid sprinkling tree and shrub leaves with water. The salts in the water can damage foliage. If you water by hand, install a faucet timer and use a soaker hose. Once or twice a year, water twice as long as you normally do to help leach salts out of the root zone. Expand the area you water as the plant grows. For trees and shrubs, water the area under the drip line of the plant and beyond. There are very few tree roots capable of absorbing water right next to the trunk. Allow soil to dry out between waterings. You want to irrigate thoroughly, but not frequently. Control weeds and turf grass growing under the drip line of trees. These plants compete for your tree's water. Prevent runoff—retain the water in a basin around the plant or water at a slower rate.

You can tell if you are over-watering if (1) leaves turn a lighter shade of green or yellow; (2) the young shoots are wilted; (3) leaves are green yet brittle. If you are under-watering, look for (1) wilted leaves, (2) curled leaves, (3) older leaves that turn yellow or brown and drop off.

Another way to decrease your use of ground water (and your water bill) is to store the water that falls from the sky for later use. More information on this technology, called rainwater harvesting, is available through this site and your local University of Arizona Cooperative Extension office.