Watering in the High Desert can be a tricky task. And there’s no easy answer for how much and how often water should be applied. It seems the best answers may be found in the soil. There are many variables that affect water usage, such as season, weather, precipitation levels and the type of plants, shrubs and trees planted. But knowing how to check water levels and moisture in the soil will help prevent over- and under-watering. Toni Stephan, small farms instructor with Oregon State University Extension, offered some tips for establishing best practices for watering.
It’s important to first know the output of the watering system being used. A measuring technique that works for automatic sprinkler systems, hand-held devices or oscillating sprinklers, to ensure all sprinkler heads are dispensing water equally, is to set out tuna or soup cans in random locations across the lawn and garden beds.
Then run the system for the same amount of time as if it were set to run a typical watering schedule and check the depth of water in the cans.
“Collect all those cans. Measure where they are and see how much water is in it so you could see if one area is getting ½ inch of water and another is getting ¼ inch and you’d want to correct the system,” said Stephan. Another indicator of uneven coverage is if certain areas of the lawn become brown in the heat of summer. This may be because those areas are not getting enough water.
After discerning how much water is being distributed, gardeners should think about the frequency for running the sprinklers. For an up-to-date location-specific indicator for recommended watering amounts, Stephan recommends using the AgriMet website: www.usbr.gov/pn/agrimet. AgiMet is a cooperative agricultural weather network that reports water usage specifications for the Pacific Northwest, with stations located in Bend, Powell Butte, Madras and Warm Springs. The “Crop Water Use” feature of the website details how much water should be applied for lawns.
In the spring, before sprinklers start running consistently, the soil should undergo a deep watering. “Because we have dry winters, our ground dries out,” said Stephan. “We want to water more frequently and longer at first so the water goes deep. We call that filling the soil profile with water.” To achieve this, do two waterings back-to-back on the same day or once two days in a row.
“You want that water to get a good 8 inches deep.” To check soil moisture, use a soil moisture probe or dig a hole that is about 12 inches deep to do a squeeze test. To perform the test, grab a fistful of dirt from the bottom of the 12-inch hole and squeeze it tightly. If the soil holds together in a ball when jiggled, the moisture is good. If the soil simply falls apart and slips through your fingers, it’s still too dry. And conversely if it’s soupy or muddy, it’s too wet. “And you need to know your soil type,” said Stephan. “In La Pine it’s pumice. Bend is primarily a loamy, sandy type.”
Once the soil profile is moistened, the regular watering regime can be maintained. An extra soak should still be planned for about once every six weeks. “Until you learn what your watering strategy needs to be, you should be doing the squeeze test so you can figure out a timeline,” said Stephan.
Annuals and turf have similar water needs.
“Annuals, you want to water like your lawn because they don’t have a deep root system,” said Stephan. Perennials, shrubs and trees require a different set of standards. In general, lawns shouldn’t be planted inside a tree’s dripline, which is the diameter of the full width of the tree’s limbs, because their needs are different. Trees should not be watered on their trunks. In fact, keeping a tree’s trunk dry is ideal. The roots of a tree spread out in a fan shape from the trunk, meaning watering should cover the soil inside the dripline.
Tree roots need oxygen, so be sure that the soil around a tree isn’t saturated with water. Because trees take their water from the top 2 feet of soil, they will be happier with a deeper soak. “If you water the tree too shallowly, the roots will grow where the water is, and if the water’s only at the top, that’s where the roots are going to go,” said Stephan.
Perennials, trees and shrubs like moisture at least 12 inches deep, and the top 3 to 4 inches of soil should dry between waterings. Watering should also be a longer and less frequent cycle than annuals and lawn. “We suggest a drip system or soaker hose where you can turn it out and let it run for three to five hours,” said Stephan.
Signs that a lawn is over-watered include the presence of leaf hoppers in the grass, mosquitoes hatching out of the lawn, moss and mushroom growth and yellowing grass. If a lawn is under-watered it will be a grayish color, won’t grow very fast and the blades won’t spring back into place when walked on. As for best time of the day to water, Stephan said that ideally, automated sprinkler systems should run in the early-morning hours and when it’s not windy. “Our lawns dry pretty well in the day, so our lawns don’t have disease.” The system should be run early enough to give the blades a chance to dry.