July's high evapotranspiration rates trigger conservation efforts

The Water Conservation Act of 2009, also referred to as Senate Bill x7-7 or “20 by 2020,” mandates that California reduce urban per capita water use by 20 percent by the year 2020. It also requires all water suppliers to increase water use efficiency.

It’s estimated that 50 percent of California’s residential water is used outdoors — to water lawns, ornamental plantings and vegetable gardens, and in swimming pools. Our water use practices can always become more efficient. 

To help us become more aware of our watering practices, July is designated as Smart Irrigation Month by the national Irrigation Association. July is the month across most of North America when evapotranspiration rates are highest. The Irrigation Association uses the phrase “saved water is money in the bank” to draw attention to the need to water landscapes and gardens, golf courses and shopping center plantings more efficiently.  

In a presentation in Groveland, Calif., Brad Lancaster, the author of “Rainwater Harvesting for Drylands and Beyond” asked the question, “Why do we use treated drinking water to irrigate our lawns?” The number one use of energy in California is to pump and move water.

Many of us in UC Cooperative Extension outreach are asked over and over during the hot, inland California summers: “How much should I water?” Although there are simple rules of thumb, the answer is, “It depends.” Effective irrigation depends on type of soil, slope, elevation, type of plants, where the plant is growing, etc.

The University of California Integrated Pest Management (IPM) website offers in-depth information for California residents interested in healthy lawn care and efficient irrigation. If you aren’t familiar with the website,  check out the interactive irrigation testing and scheduling tools.

In addition to efficient irrigation scheduling, there are some fairly simple (and some not-so-simple) techniques that can help reduce outdoor residential water use:

• Check watering depth. A long screwdriver blade will penetrate easily into damp soil.   Use it to gauge how deeply water is penetrating.
• Add organic material to the soil. Compost, homemade or purchased, helps clay soils drain and helps sandy soils retain moisture. Compost also reduces water demands, helps control soil erosion, and reduces plant stress from drought.
• To combat evaporation, plant closely enough that plants shade the soil.  
• Mulch, mulch, mulch, mulch to slow evaporation from the soil surface.
• The amount of water needed varies by species of plant, the time of year, the amount of sunlight, air temperature, etc. The general rule of thumb is that turf grasses use up to about a quarter inch of water per day during the hottest part of the summer. To replace that almost two inches of water per week, divide the amount of water needed into one to three irrigations per week.
• Consider replacing some plantings with drought-tolerant natives.
• Consider reducing lawn size. 
• Check sprinklers for leaks, broken heads, misaligned spray patterns and run-off. 
• If water is running off, “cycle” irrigation. Run sprinklers until run-off appears, stop until water infiltrates, and repeat until deep irrigation is achieved.

For more information, see the UC Guide to Healthy Lawns.