CONSERVING WATER IN THE GARDEN Landscape and Lawn Care ',\V' R.A. McNeilan, J.L. Green, and N. Goetze EM 8374 • Reprinted July 1992

During a severe drought, when building, for example). Previously "Drip," "trickle," and other the use of water supplies is re- weakened or diseased plants may also "microsource" methods of irrigation stricted, homeowners become perish. can reduce water loss and require- concerned that their plants may die. ments by as much as 50% compared By developing watering priorities, Use conservative methods to overhead sprinkler irrigation. and by planning for effective use of Where to apply. Water uptake by the DATE. available water, you can provide plant occurs primarily at the root tips Use waste water? some measure of insurance against and through the fine root hairs A question frequently asked is, plant loss to drought. immediately behind the growing root "Can I use waste water, even if it You might set these priorities: tip. Very little water or fertilizer is OFcontains detergents and soap, to Trees. As trees increase in size, taken up through the older, discolored irrigate my plantings?" According to they become increasingly valuable. portion of the root. the Oregon Department of Environ- Give mature trees top priority to The growing root tips and root mental Quality, no untreated waste receive a deep root watering weekly hairs are located primarily beneath the water may be used to irrigate plantings. during droughty conditions. drip line (imagine a circle on the 'Treated water" is defined as water Shrubs. Shrubs in good health and ground that follows the edgeOUT of the that has been run through a munici- good form—that have been estab- plant canopy). Apply your limited pal waste water treatment plant. lished for several years and are water to these root zones only. For contributing significantly to the IS example, adjust a hose to discharge a Mulch to conserve water overall landscape picture—should be small amount of water and place it at Choose the right mulch for your second to trees in priority. New the edges of the plant. shrub plantings of relatively low Better yet, try subirrigation: Punch purpose. A mulch that will reduce initial cost or old, overgrown, holes in the bottoms of juice or coffee soil temperature, decrease surface misplaced shrubs may not be of such cans; insert these (or pipes) around moisture evaporation, and decrease great value. If you value new the plant's edges; push them down to weed competition for available landscape material, give it a high the root zone, information:where the majority of moisture will diminish water deple- priority for watering during the first root hairs are located. Apply water tion and evaporation from the upper growing season. through these open columns directly 6 to 8 inches of soil. Perennial plantings. Maintain to the root zone, where most active Tests show that merely shading plantings of rare perennial plants or uptake will occur. This will greatly the bare soil will reduce evaporation plants of high initial cost and give reduce evaporation and unnecessary as much as 30%. Mulch will reduce them a high priority. Their water wetting of surrounding soil. evaporation by as much as 70%—and requirements compared to trees and When to apply. The most effective promote a more uniform moisture shrubs are relatively low. currenttime to minimize evaporation losses supply in the upper layers of the soil. Annual bedding plants.PUBLICATION If you want and plant diseases is very early morn- Mulching materials may be to maintain annuals, you'll need to ing, preferably before sunrise. classified as plastic film and organic. emphasize mulching (see "Mulch to What to use. Avoid irrigating A combination of plastic film mulch conserve water"). ornamental plantings with a sprinkler. covered with up to 2 inches of Lawns. Many varietiesmost of grass are Much of the water may be lost to relatively drought-resistant—they evaporation before it reaches the Revised by Ray A. McNeilan, Extension mayTHIS look bad under drought condi- ground surface. agent (home and urban horticulture), tions, but they'll survive. Subirrigation (the cans or pipes Multnomah County; James L Green, A drought year may be the one outlined above) conserves the most Extension ornamental horticulture when plantsFor that you placed in the water. specialist; and Norman Goetze, Extension wrong locations fail to survive agricultural program leader, emeritus, (azaleas on the southhttp://extension.oregonstate.edu/catalog side of a Oregon State University.

ORGGON STATG UNIVGRSITY GXTGNSION SGRVICG organic mulch is very effective in Sawdust and barkdust. Redcedar Lawn care lowering soil temperatures, control- sawdust and bark (unleached) Lawns can probably be allowed to ling weeds, and maintaining good reportedly contain materials poison- go dormant from drought for the ous to plants. Other wood sawdust soil structure. summer. They will renew themselves and bark make an effective mulch. Plastic film mulches. Don't use clear when the fall rains begin. Drought- plastic film-it allows the sun's rays to Conifer needles make a light, airy, stressed lawns can be seriously enter the soil, producing soil tem- attractive mulch. Pine needles are damaged by heavy use. Avoid traffic moderately acid; they're desirable for perature increases of lOT or more. as much as possible. use as a mulch for acid-loving plants Soil temperatures may become so Western Oregon. In the spring, as (azaleas, blueberries, etc.). high as to kill plant roots. High soil rains are still occurring, plan to Bark chips are one of the most temperatures increase water require- toughen the grass to withstand a long, ments of the plant and increase desirable organic mulching materials. dry summer. In mid April, apply a They're long-lasting and not easily moisture loss due to evaporation. commercial fertilizer containing compacted. Clear plastic film may allow weeds nitrogen (3 to 4 parts), phosphorus (1 to become a problem underneath the There are numerous other materi- part), and potassium (2 parts) at a als that you might use as mulches if film. In general, clear plastic is not light to normal rate. Don't use heavy recommended unless you apply an they can insulate the soil—and rates of fertilizersDATE. when you expect organic mulch like bark over it to thereby reduce soil temperature, summer drought conditions. reduce surface moisture evaporation, eliminate sunlight. Eastern Oregon. Withhold the first Black plastic film excludes sunlight and control weeds. fertilizer until the lawn turns green, transmission and, therefore, doesn't OFafter the breaking of the winter cause as large a temperature increase Don't stimulate dormancy. See Extension Circular as the clear film does. Excluding light excessive plant growth 1287, Fertilizing Home Lawns, for more also prevents weeds from growing Fertilize lightly. Heavy fertilizer information. underneath the film. applications increase the salt concen- Note: Before you apply any plastic tration around the plant roots and film mulch, make sure your soil is make it more difficult for OUTthe plant to damp. Do not mulch dry soil. use whatever moisture might be in Organic mulches. Apply organic the soil. materials with a small particle size OverfertilizationIS may also stimu- (like sawdust) only to a depth of 1 to late new, lush growth that increases 2 inches, to avoid excessive compac- the plants' demand for water. If tion and to allow air exchange water is already limited, this in- between the soil and the atmosphere. creased water demand will make the You can apply coarse or fluffy plants more susceptible to drought. materials that don't readily decom- pose or compact (like bark chips) 3 to Don't heaxnlyinformation: prune trees or shrubs. 4 inches thick. Heavy pruning during late winter or Apply mulch evenly—don't pack spring stimulates new, lush growth it around the stem or trunk of the and increases the plant's susceptibil- plant. When the mulch is thoroughly ity to drought damage. wet, pull it back a few inches from In the spring, do only corrective the stem or trunk so there is free air pruning—remove dead or diseased Extension Service, Oregon State Univer- circulation to the base of the plant. branches. You'll reduce water use if sity, Corvallis, O.E. Smith, director. This Lawn clippings may be used as currentyou prune off leaf surface during the publication was produced and distrib- mulch after they havePUBLICATION become dry. summer. uted in furtherance of the Acts of Con- Thick layers of fresh grass clippings If soil moisture is extremely short, gress of May 8 and June 30,1914. Exten- may mat down, get slimy and smell you might consider careful, selective sion work is a cooperative program of bad during decomposition, and removal of leaves, however, do it in Oregon State University, the U.S. Depart- such a way that inner, shaded leaves ment of Agriculture, and Oregon coun- decrease air circulation to the soil. ties. Apply 3A to 1 inch in a mostlayer at a time won't be sunburned. Here's help. A good source of to avoidTHIS this. Don't use grass clip- Oregon State University Extension pings if you've treated the lawn with information on water conservation is Service offers educational programs, a weed-killer. Ortho's Weather-Wise Gardening activities, and materials—without regard Leaves, previouslyFor composted, are (Western edition). The sections on to race, color, national origin, sex, age, or more satisfactory. Noncomposted "Mulches as Modifiers" and "Drip/ disability—as required by Title VI of the leaves, like fresh grass clippings, may Trickle Irrigation" are especially Civil Rights Act of 1964, Title IX of the compact and producehttp://extension.oregonstate.edu/catalog heat during appropriate. It's available at most Education Amendments of 1972, and decomposition. garden shops. Section 504 of the Rehabilitation Act of 1973. Oregon State University Extension Service is an Equal Opportunity Em- ployer.