Saturday, December 3, 2022
Dec. 3, 2022

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Gardening With Allen: Timing matters in irrigation


I have been irrigating every day during this 90-plus degree weather we have had recently. Is it time to decrease my irrigation?

It looks like our day and night temperatures are moderating enough to decrease our irrigation. Also, day length has shortened by several hours since late June. The reduced amount of sunlight has reduced plant water use by 20 to 30 percent. It would be better to increase the time between irrigations rather than reducing the amount of irrigation time. I would suggest going two days and maybe even three days between waterings. Container plants may still need daily irrigation because the plants have grown to a larger size.

Short, daily irrigation causes plants to have shallow roots because only the top inch or two of soil is moist. Keeping the top of the soil moist also encourages weed seed germination.

In general, enough water should be applied in each irrigation to reach a depth of 6 inches. This varies from about ¼ to ½ inch of water, depending upon soil type. For automatic systems, the length of time needed to apply this much water depends on the type of sprinkler heads, pipe size and water pressure.

Whether or not you have an automatic system, you can determine how long you need to water to deliver ¼ or ½ inch. Place shallow cans at both wet and dry locations. Run the sprinklers for a specific amount of time such as 10 minutes. Then measure the amount of water accumulated and calculate how long it will take to deliver ¼ or ½ inch. Then adjust the amount of sprinkling time so that dryer areas will receive ¼ or ½ inch. By placing several cans at different distances from sprinkler heads, you will also discover how uniformly your system applies water.

You will probably find that some areas receive twice as much water as others. If differences are greater than 50 percent, you may need to clean, adjust or replace some sprinkler heads. Plants may also grow to block part of a sprinkler pattern. That may require you to trim the plant or move the head slightly. Sometimes a new head needs to be added.

The best time of day to irrigate is between midnight and mid-morning. Less water evaporates when the temperature is low and the sun is not shining. Plants suffer less disease when their leaves do not stay wet for more than six hours. Sunlight right after irrigation helps leaves dry out quickly.