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Watering the Lawn: Soak and cycle

by Dennis Patton, horticulture agent.

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Knowing how to water your lawn during the stressful summer conditions is difficult for just about everyone. Soak and Cycle takes the guesswork out of lawn watering, and ends the debate over light-and-frequent versus deep-and-infrequent watering. Soak and Cycle mimics Mother Nature’s natural rainfall cycle by soaking the soil and then allowing the soil to slightly dry. This combination develops a soil condition that encourages strong roots for a more drought tolerant and disease free lawn.

What is Soak and Cycle?
The Soak and Cycle method works best for sprinkler systems. But for hose draggers like me, it has merit. The theory behind the method is to soak the soil to a depth of 6 to 8 inches, which is the desired depth grass roots should grow, to develop a nice, healthy lawn.

The cycle phase refers to the fact that water is not applied at a rate faster than the soil can soak up, thus reducing runoff and waste. So, first we soak, allowing that water to move into the soil; and then we wait; then soak again; and maybe even again, until we have applied up to the recommended 1 – 1½ inches of water per week needed for a lawn to remain green during the blazing heat of summer.

How much water can local soils absorb?
Kansas City’s heavy, compacted clay soils have a very slow infiltration rate. In fact, university research shows that our local soils cannot absorb more than two-tenths (.2) of an inch of water in one hour. How much your soil can absorb depends on its type, slope and other factors. A flat area can take up more water per hour, while a slope may start to run off after two-tenths is applied, with the rest of the water running off into the gutter and down the storm drain. Simply stated, if you add water faster than the soil can absorb it that’s wasted water — and wasted money! Who can afford that?

How much water does your watering system apply?
Do you know how much water your sprinkler heads apply? If you don’t know how much you are applying then how do you know how long to run the sprinklers in order to achieve the desired goal of 1 inch of absorbed water? Or, do you just water to keep the grass green and alive, which probably wastes water and increases disease and root problems?

First, you need to know how much water your watering system puts out in a given amount of time. To determine the flow rate of your sprinkler system, set several rain gauges or empty straight sided cans (tuna cans are ideal) in each sprinkler zone so they are within the spray pattern of the sprinkler heads. Then, run the system for a set amount of time — we recommend 30 minutes. Shut off the sprinklers and measure the amount of water collected in the zone. Pour all the water into a single can. When using a tuna can take it to a flat surface and measure the depth of water with a ruler. Divide that number by the number of collection cans. This determines the average amount of water that particular zone applies during a 30-minute time period. This is called the flow rate.

Congratulations! Now do it again for each and every zone in your sprinkler system, because chances are each zone has different kinds of sprinkler heads that put out different amounts of water.

Soak: flow rate VS absorption rate
Remember what I said earlier about how Kansas City soils can typically absorb only two-tenths (.2) of an inch of water in one hour? Because you now know your flow rate (how much water your system puts out per zone per 30 minutes), you can set your timer so the system only puts down two-tenths (.2) of an inch of water, soaking that zone with only enough water without it running off. Congratulations! You are now ready to Cycle.

Cycle means to switch to a different zone in your lawn and water it for the correct amount of time determined in your empty can test. This allows the water applied to the previous section to soak into the soil. After you’ve applied the requisite two-tenths (.2) of an inch to the second zone, then go back to the first zone and soak again. Keep in mind, the Soak-and-Cycle method may require several soakings and rest periods in order to apply the needed 1 inch of water per week to keep the lawn spring time green. So this means that on any one day the same area or zone may be watered three or four times.

How often should you water your lawn?
If you use the Soak and Cycle method, the area or zone is not watered again until the soils dry and the grass starts to wilt. In the hot Kansas City summer, lawns lose about one-third of an inch of water each day. So based on the Soak and Cycle method, once the soil has absorbed a total of 1 inch of water it will probably take about three to four days to dry out to the point of needing to be watered again. This means that your entire system still may run every couple of days, but not the whole yard, just the zones that are ready for their round of Soak and Cycle.

Soak and Cycle ends light, frequent applications of water
People traditionally run their systems over the entire lawn every few days, three or four times a week. They probably have no idea how much water is being applied. This practice concentrates all of the water in the upper few inches of the soil, and encourages the development of a shallow root system and disease prone plants. With Soak and Cycle, each area is soaked about every three to five days, depending on the zone’s particular attributes, such as sun, shade, slope, soil type and other factors.

Sound difficult? It’s not.
I know this is a lot to absorb, pun intended. But it really only requires you to do three simple steps:

  • Step 1 – Determine the flow rate of your sprinkler heads.
  • Step 2 – Re-program your timer clock to Soak and Cycle the zones, based on that zones flow rate. Remember, the same zone will be watered several times on the same day. Your sprinkler system might still run just about every day, but you’ll be watering different areas each day.
  • Step 3 – Monitor the lawn for a few weeks and make adjustments based on the various conditions.

The concept of deep and infrequent lawn watering is not new. But the method for achieving a deeply irrigated lawn has been modified because of research. Once you’ve figured it out, it takes the guesswork out of the watering-the-lawn equation. You’ll know just how much water is being applied;

  • the amount of time in which the soil can absorb it; and
  • create the ideal conditions for the development of a healthy root system that can withstand the traumas of our Kansas City summers.

So, give it try and stop the light, frequent applications of water to your lawn that helped create the horrid conditions that lead to last year’s lawn collapse in the heat of summer.

Other Resources

Summer Lawn Care Tips

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