A bit about hydrozoning
I received a call recently to perform a regular irrigation-system inspection. The system was working perfectly. My clients had received a 10,000-gallon water bill, had called the city, and were assured they had no leaks.
It turns out they have one very large irrigation zone and it is set to water 53 minutes three times a week. This zone includes trees, shrubs, and flower plants. Watering 160 minutes a week is a lot for a flowering plant 10 inches tall. The trees probably don’t like the watering time, either. I guessed the irrigation professional in charge of the property had turned it up to give the aspens on the far side just a little more water!
Hydrozoning comes from “hydro,” the Greek root forwater and “zone,” meaning to group together in some fashion. Trees, shrubs, and vegetables have differing watering needs. This is the central tenet of hydrozoning, which considers plant type, soil type, and site-specific climate conditions to determine schedules for watering length and frequency. Plants with different watering schedules are put on similar irrigation zones. Trees go in one zone, flowering bushes in another, and xeric plants in another.
Hydrozoning has been around for years, but is not widely practiced. It can save substantial amounts of water, but requires planning. By grouping plants with similar watering needs in the same zones, plants can be accurately watered. Additionally, various plants require different irrigation methods. Grasses are watered with spray or rotor heads, while flowering plants typically get micro-drip heads.
As Dan Ransom, the previous water-conservation manager for the City of Santa Fe liked to say, “Plants don’twaste water; people do.” Without hydrozoning, the irrigation systemmust always be set to run too long just to satisfy the watering requirements of the largest or thirstiest plant in the zone. Watering low-water plants such as lavender, yarrow, Russian sage, and trees too oftenwill cause them to suffer. Your flowering bushes may survive but not be as beautiful as they can be. Usually trees should be watered once a week for about an hour, shrubs two or three times a week for 15-20 minutes, and flowering plants three or four times a week for 5-10 minutes. This change will save thousands of gallons a month.
My client’s watering schedule will keep expensive trees alive, but stresses everything else. The solution is to split the system into multiple zones: one for the trees, one for the shrubs, and one for the flowering plants. Just splitting the trees from the rest of the plants will save water every week. That way the trees can get long, deep waterings; while the rest of the plants will get shorter, more frequent waterings.
The Santa Fe Landscaping Irrigation Design Standards (LIDS) guidelines are a great source of information about designing an efficient and functional irrigation system. The LIDS document can be downloaded free at www.santafenm.gov/ water_conservation.
Installing new irrigation lines in an existing landscape can be expensive and invasive but will pay for itself in many ways. Your plants will look better, your water usage will be less, and your pocketbook will be bigger. It’s a win, win, win!
Doug Pushard, founder of the website www.HarvestH2o.com, has designed and installed residential rainwater systems for over a decade. He is a member of the Santa FeWater Conservation Committee, a lifetime member of the American Rainwater Catchment Systems Association, and an EPAWaterSense Partner. He can be reached at doug@HarvestH2o.com.