Products, Vendors, CAD Files, Spec Sheets and More...
Sign up for LAWeekly newsletter
The moment a landscape project is completed, the Landscape Architect starts to wonder: As the years go by, will the project achieve the grace and finish that only wellgrown plants can create?
Intelligent and well-implemented maintenance can answer a resounding yes. Landscape Architects can channel the efforts of the grounds maintenance crews and guide the garden to its prime by including maintenance standards in every design package. In the desert climate of the Southwest, where imported water is an expensive and essential part of landscape maintenance, those standards must include irrigation guidelines. The Landscape Architect who fails to do so may be left high and dry.
The staff at David Reed, Landscape Architects, in San Diego,decided to test the waters and develop an irrigation guidelines package. They were assisted by Dave Shaw, Landscape Advisor in the San Diego Office of the University of California.
They have made the guidelines as compact as possible, but broad in scope. A groundskeeper may need a basic education in irrigation, so the guidelines need to outline the why’s, of sprinkler design. It is also essential to provide the patterns and precipitation rates of equipment in each zone on the particular project, and to describe approximate water needs for plants in San Diego.
These guidelines assume the San Diego yearly average rainfall of about 10" per year, all falling between December and March. Schedules also assume the following average temperature ranges:
January through March: 35????? – 65????? April through June: 60????? – 80????? July through September: 70????? – 95????? October through December: 40????? – 75?????
If the weather differs markedly, the scheduling must be adjusted. When rainfall of 1/2" or more occurs in a 24-hour period, an automatic sensor such as Rain Guard?EUR??,,????<
If unseasonal weather occurs, or if plants appear to be understress or soils too wet, gardeners must check the amount of moisture in the top six to nine inches, by simply probing with a sampling tube, spade or trowel, or by installing tensiometers for every exposure on the project. There is no other way to be sure that the sprinkler schedule is optimum.
Multiple start, dual program controllers are a blessing in San Diego, because most San Diego soils have high quantities of clay. This results in very slow percolation As little as 0.15 inches of water can be absorbed per hour in high clay soils Amending soils with gypsum, humus, and products like Sarvon?EUR??,,????<
Most spinklers (except drip-type systems) apply three to eight times this amount in an hour. If the soil absorbs only 1/4" per hour, the head delivers 1" per hour, and you need to give the plants 1/2" the sprinklers will need to be turned on for 15 minutes twice, e.g., at 6 A.M. and 7 A.M. With a multiple start programmable computer, this is easy. Water penetration, and therefore conservation, is also improved by requiring gardeners to maintain 1 1/2" of ground bark mulch under all shrubs and trees, and by creating shallow water wells around them for the first year. In addition, every project with static water pressure that exceeds 60 psi includes a pressure regulator to provide working pressures of 25 to 35 psi. Sprinklers that “fog out” at excessive pressure are the source of a lot of wasted water.
The best time to irrigate is the early morning hours (e.g., 5 – 7am and 9 -10am), avoiding peak domestic use periods Watering at midday wastes water to evaporation. Irrigation at night encourages fungi and other pathogens. Also, pipe damage at night will not be seen until morning, by which time property damage may occur and water will have been wasted.
Each zone is listed in the guidelines, along with the type of sprinklers, their precipitation rates, and the type of plant association. (SeeFigure1) David Reed’s experience has led his office to use certain sprinkler types for particular situations. Hunter gear-driven rotaries are specified for uniform large areas because of a low 0.4" per hour precipitation and good, solid construction. Hardie end and side strips, with 1.4" per hour precipitation rates and a low splatter pattern, are compatible with Toro 570 series 12' nozzles. If a sprinkler breaks, the gardener must replace it with an identical head.
Plants are grouped as much as possible to have similar needs within each sprinkler zone. These needs include: growth habit; rooting depth; sun and shade exposure; slope; soil type; wind; and climate. Gardeners are cautioned not to introduce new plants unsuited to these conditions.
The sprinkler guidelines chart the approximate amount of water needed for different plant associations. (See Figure 2) The quantity is partially supplied by rainfall, and the rest by irrigation. The gardener is given approximate amounts, and can then fine-tune the schedule by checking soil moisture.
These types of plants require the most water, averaging approximately 60" per year. A few may need more. However, studies of commercial landscapes in San Diego have shown that 100" to 150" of water are poured on these landscapes, in a misguided attempt to give them enough water. In fact, ailing plants are often victims of “drowning” in poorly drained clay soils. By closely monitoring soil moisture, water use may even be reduced below 60" by encouraging deep rooting through less frequent, deeper irrigation.
These grasses require approximately 45” of water per year. Bermuda is dormant in the winter and does not require water when temperatures fall into the 50’s (degrees F). However, if Bermuda is overseeded with an annual rye for winter green, the gardener should schedule the irrigation as for cool season grasses.
These plantings require as much as 45" of water per year. Many plants require much less, surviving exclusively or largely on winter rainfall. By carefully monitoring plant health, irrigation may be reduced. However, unless there is a note to the contrary on the plans, the schedule should be followed.
Drought-tolerant ground covers and shrubs are selected for most slopes because less water penetrates on slopes. These plants require approximately 36" water per year. Because water runs off slopes, the scheduling must be broken into even more, and briefer, starts than on flat areas. One half inch of water may need to be applied in four ten-minute starts, over a four-hour period.
These schedules are for established plantings. When plants are installed from a nursery, they need more frequent, shallower irrigation. After the first summer, the plants can gradually be put on their permanent schedule. Also, after trees grow and their canopies get bigger, areas shaded by the trees will need less frequent, but deeper, irrigation.
The guidelines are placed in a plastic sleeve inside the controller cabinet. Any time the gardener needs them, they are close at hand. Plants should be healthier, and waterbills much lower, if the guidelines are followed.
As time goes on, David Reed’s office expects that the guidelines will be improved by the comments of the users in the field. Irrigation may be a dry subject, but the more the Landscape Architect and the maintenance staff are talking about it, the higher the odds that a planting design will grow to reach its highest potential.
Francisco Uviña, University of New Mexico
Hardscape Oasis in Litchfield Park
Ash Nochian, Ph.D. Landscape Architect
November 12th, 2025
Sign up to receive Landscape Architect and Specifier News Magazine, LA Weekly and More...
Invalid Verification Code
Please enter the Verification Code below
You are now subcribed to LASN. You can also search and download CAD files and spec sheets from LADetails.