Gardening with Allen

Sprinkler basics

I recently had a new sprinkler irrigation system installed for my home. At the recommendation of the contractor, I had drip irrigation installed in my beds. I am anxious to get the most efficient use from my new system without wasting water. Could you give me some pointers on seasonal programming of my system.

Answer: I am glad you said “seasonal programming” because irrigation systems do need to be adjusted during the summer. However, most irrigation controls have a seasonal control which allows you to increase or decrease irrigation by a percentage amount during the season. So if you get the system set at the beginning of the season, seasonal adjustment is simple. However, changing the interval between irrigation days can complicate adjustments.

The amount of water applied by different types of sprinkler heads varies considerably. Spray type heads that apply water to the entire area while they are on apply water at the most rapid rate. Some spray type systems rotate and apply water to a specific area only part of the time that they are on. Some rotating systems (often referred to as rain bird) only apply water to a small part of the area while they are running. These types of sprinkler heads may need to be left on up to 4 or 5 times as long a spray heads. So if a spray head requires 10 minutes to apply the correct amount of water, rotating heads may need to be programmed for up to 50 minutes to apply the same amount of water.

Drip irrigation is much slower and it may require two hours to apply the same amount of water as a 10 minute spray head.

In order to get the full root system moistened it requires about ½ inch of water. Then the soil should be allowed to dry out between irrigations. This avoids keeping the top of the soil moist which encourages weed seed germination. This time of year a 3 or 4 day interval is usually adequate. During the hottest part of summer, a 2 day interval may be necessary.

If you are not sure how long it takes to apply ½ inch of water with your different types of sprinkler heads, set shallow cans such as tuna fish cans at intervals and turn sprinklers on for a timed period such as 10 minutes. Measure the amount of water in the bottom of the cans and calculate the time needed to apply ½ inch.

With drip systems, the best way to check is to open the soil with a trowel or shovel and see how far the soil had been moistened after irrigation.

The longer days and warmer temperatures of mid-summer combined with less rainfall may mean doubling the amount of irrigation. Then as days shorten and cool in the fall, irrigation can be reduced again.

 

Allen Wilson

Allen has been writing about gardening for over 30 years. He is a retired professor of Horticulture. Additional gardening information is available on his web site: naturalpruningnw.com under "how to guide". A monthly email garden newsletter can also be signed up for on this site or by sending a request to allenw98663@yahoo.com.

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