in this Issue
Saving Water Starts With Some Simple Changes in Garden Care
By Vincent Lazaneo
You don’t need to redesign your landscape to have a beautiful yard and use less water. How you care for plants will influence the amount of water they use. Simply adjusting a few horticultural practices will help you save both water and money. Just follow the plant care tips described below and be a Water-wise gardener.
- Apply less nitrogen fertilizer.
When you give plants fertilizer containing nitrogen (the first of three numbers on a fertilizer package), they respond by producing more tissue, especially leaves. Producing a lot of new leaves is desirable when a plant is young and you want it to grow larger, but vigorous growth is usually NOT needed on a mature plant. Leaves make food for the entire plant, but they also let water escape through tiny pores. The more foliage the plant has, the more water it will use and young leaves loose water faster than mature leaves.
Giving a plant less nitrogen fertilizer will reduce the amount of new foliage it produces and this will decrease the plant’s water use.
To save water, fertilize young woody plants at half the rate listed on the product label, and increase the interval between applications of fertilizer. Most mature ornamental trees and shrubs do not require any nitrogen fertilizer if they have good foliage color and density. When additional growth is desired, apply fertilizer containing nitrogen in the spring at half the recommended rate when new growth begins.
A lawn should not be fertilized if it produces a lot of clippings when you mow. You are not trying to grow a crop of hay. Only apply enough fertilizer to maintain good lawn color and density. Over fertilizing cool season turf grasses like tall fescue (Marathon) in summer when the weather is hot weakens the turf and makes it more susceptible to damage from diseases and pests.
- Prune lightly or not at all.
Heavily pruning trees, shrubs and vines in summer will stimulate the growth of new shoots and foliage. The new foliage will loose water faster than mature leaves. Removing shoots from the exterior of a plant will also expose interior foliage to more sun and wind which will increase water loss.
To save water, do not prune woody plants heavily after spring growth has matured. Only remove dead or broken branches and prune healthy growth lightly if necessary. Remove shoots where they join another branch or the trunk. Do not leave a stub when shoots are removed since this will stimulate more sprouts just below the cut. If possible, delay pruning hedges until fall when days are shorter and the temperature begins to cool.
On cool season lawns increase the mowing height to, at least, two inches. The additional foliage will promote deeper rooting which will let the lawn go longer between irrigations.
- Remove weeds and other unwanted plants.
Weeds and unwanted plants growing in a landscape remove precious water from the soil and compete with the more desirable plants you want to grow. Remove weeds as early as possible to conserve soil moisture and prevent seed production. Also remove weak and unwanted ornamentals so you won’t waste more water on them.
- Use mulch and keep it dry.
Water evaporates from the surface of wet soil after irrigation or rain. As the surface dries, more water moves upward from wet soil below. The loss of soil moisture from evaporation can be reduced by applying a 3-4 inch thick layer of medium textured bark or similar mulch on top of the soil around trees and shrubs. The mulch helps control weeds and protects the soil’s surface from sun and wind.
Mulch can be applied directly on the soil or on top of a layer of weed block fabric which is more effective in controlling weeds. To maximize water savings the mulch should have a medium texture with pieces about one-inch in size. This will allow water to pass quickly through the mulch into the soil and not be retained by the mulch. Avoid using compost or other fine-textured mulch which acts like a sponge, and holds a lot of water that will soon be lost through evaporation. If sprinklers are used for irrigation, water plants thoroughly and as infrequently as possible to keep the mulch dry and optimize its water-saving potential.
- Plant in the ground, not in containers.
Plants grown in containers, especially in small ones, require more frequent irrigation and use more water than the same plants grown in the ground. If you use containers, select those made with a material that insulates the soil from heat such as wood or plastic with a double-wall construction. Ceramic containers can be used if you place a plant growing in a plastic pot inside them and fill the space between the plastic and ceramic containers with an insulating material like coarse perlite. Also, group containers together so that they partially shade each other.
- Limit use of pesticides with oil or soap.
The protective waxy cuticle on plant leaves is damaged when plants are sprayed with pesticides that contain petroleum products like oil or surfactants like soap. This increases water loss from foliage. To save water in landscapes, encourage natural enemies to control pests when possible (for more info, see UC Pest Note 74140 – Biological Control and Natural Enemies) and only apply pesticides when necessary. If a horticultural oil or soap is used to control soft body insects like aphids or white flies, rinse the plant off with plain water one or two hours after treatment.
- Make every drop count.
Irrigation systems often apply water faster than soil can accept it, especially on hillsides. To save water, stop irrigating when run-off begins and wait at least an hour for water to soak in. Repeat this on/off cycle for as many times as needed until water penetrates to the desired depth.
Always try (if irrigation restrictions permit) to wet the soil to the depth of the plant’s root system. This is about 6 inches for turf grass; 12 inches for small shrubs; and 24 inches for large shrubs and trees. Before you water trees and shrubs, dig a few inches below the surface to check soil moisture. Wait until the soil begins to feel dry before you water again.
The more water you give a plant, the more it will use. Plants use less water when the soil begins to dry out. To save the most water, irrigate thoroughly then allow the soil to dry somewhat before you water again.
Vincent Lazaneo is Urban Horticulture Advisor for UC Cooperative Extension. He helped found the San Diego County Master Gardener Association more than two decades ago and serves as its advisor. He is the author of numerous articles on plants and pests that appeared in the San Diego Union-Tribune, California Garden and other publications.