JoAnne Skelly: Be water wise as temperatures heat up
July 1, 2014
Summer means heat. Heat stresses trees, shrubs, flowers, lawn and vegetable gardens. Everyday lawns, trees and other plants lose water in a process known as evapotranspiration, similar to sweating. As temperatures increase, the length of time for irrigation should increase.
Plants draw water out of the soil through their roots, up their stems and lose almost 99.9 percent of this via pores on the leaves. This is the transpiration part of ET. Evaporation occurs off the soil or off plant surfaces rather than through the plants. Knowing the amount of the ET loss enables homeowners to replace it in quantities sufficient to maintain plant health. The goal of irrigation is to replace all the water lost through evaporation and transpiration. When soil moisture is insufficient to meet the ET demand, the plant starts slowing down its processes. If soil moisture is not restored, the plant eventually dies.
ET is determined by the drying potential of the air. This is affected by solar radiation, temperature, humidity and wind. As temperatures rise, plants lose more water through ET in order to cool leaf surfaces. Higher humidity lowers the rates of evaporation and transpiration. Wind increases water loss through ET. By giving plants only what they actually need, they will be healthier and water will be used without waste.
In April, your lawn may only need one-half inch of water per week. When the temperatures climb to 100 degrees in July, lawns may need more than two inches of water per week. The key is to adjust your irrigation timer to meet the demands of the season. If you set the timer for too long a duration too early in the year, you waste a lot of water. If you leave the duration set for April too long into the summer, your lawn and other plants can really suffer. The watering schedule that worked in April is too short for July.
Washoe County has an informative ET website http://www.washoeet.dri.edu/.
On the front page is the total amount of water to apply that day based on the three-day per week watering cycle and certain sprinkler head types. ET is measured at weather stations across Northern Nevada. There is a calculator to estimate your sprinkler runtime based on water pressure, delivery rate and other factors.
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JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at firstname.lastname@example.org or 887-2252.