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Index : Watering
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- 23. Cut Back on Cool Season Watering - Top
- With the cool weather of fall and winter comes a slow down of plant growth. Corresponding to this slowed growth, is a reduction in the need for water.
If you still have your irrigation set to deliver the frequent watering of summer, now is the time to adjust for winter. Lengthen the intervals between watering. For example; if you've been irrigating your landscape every three days, water every 6 days for now. Later, as the temperatures get colder, set it to come on every 12 or 14 days. The point is, continue to lengthen the intervals between watering as the temperatures cool and the days shorten.
Some types of plants will require more frequent irrigation than others. Fall vegetables and flowers may need daily irrigation until establishment. Then watering can be gradually reduced to once a week. Desert adapted trees and shrubs will need little or no supplemental irrigation through the winter.
The amount of water to put on per application should not change from summer to winter. Water long enough to wet the soil to a depth of 18 to 24 inches for small plants like flowers, vegetables, ground covers and small shrubs. For larger shrubs and trees wet the soil to a depth of 24 to 36 inches.
The best, and only practical way to determine if your running your irrigation long enough, is to check the soil moisture after watering. Say you normally run your drip irrigation 1 hour per watering. After the 1 hour, use a sharp metal rod, such as rebar or a long screw driver to test the depth of wetting. Push the rod down into the soil. The rod will go easily though moist soil. When it hits dry soil it will stop. Measure the depth the rod has been pushed in. If the depth of wetting is too shallow, increase the run time. Adjust the run time until the proper wetting depth has been achieved.
Fall is a great time to make adjustments to your irrigation system. Check drip emitters for clogs and rodent damage. Replace any damaged emitters. Also check for leaks. If your irrigation lines are buried within the top 6 inches of soil, leaks will show up as wet circles on the soil surface, away from any drippers.
While water requirements are low, add more drip emitters before water demands increase next spring. As trees grow, their roots rapidly expand. Tree root can grow as much as 3 foot per year. At maturity roots extend out 1.5 to 4 times farther than the branches. Obviously 1 or 2 drippers at the base of even a young tree, is insufficient.
At a minimum, place enough drippers under a tree or large shrub to evenly wet the entire area under the branches. For example, a tree with branches that extend out 5 feet from the trunk would need 5 drippers in a clay soil. A tree with branching 10 feet out would need 18 drippers to cover a good portion of the root zone. The point being, most trees and shrubs are grossly under watered, based on the number of drippers commonly used. In sandy soils where water does not spread out, as it does in clay, even more drippers are needed. As many as 5 times the number of drippers may be required for a sandy soil verses a clay soil.
Finally, don't mix drip emitters. All emitters on an irrigation zone should have the same gallonage output. Some emitters put out as little as 2 gallon per hour, others as much as 2 gallons. If you mix the emitters, the soil will be moistened to varying depths. Some areas will be watered too deep, others too shallow. Only when all the emitters are matched in their gallonage output can you consistently water the root zone.
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Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona 626-5161.
Material originally appeared in Arizona Dailt Stargardening column, on November 10, 1996
- Updated: November 10, 1996
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