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.

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