By Matthew R. March, MNRD
Polk County Extension Agent
This summer started off with heat and drought that surprised many of us. Home gardeners and homeowners have been caught off guard with their gardens and lawns suffering from lack of rainfall and extreme heat. Don’t water enough and you’ll end up with a thinning or dying lawn. Yet, water too much, or at the wrong time of day, and you will be full of fungal diseases that can also kill your lawn.
Automatic irrigation sprinklers can be of great help and a wonderful tool, if you know how you should use it. Rather than watering on the same schedule each week, adjust your water timer according to the weather. And when you need to irrigate, irrigate deeply. Then wait until the grass begins to show signs of drought stress before watering again. Symptoms of drought stress include grass leaves turning a dull bluish color, leaf blades rolling or folding, and footprints that remain in the grass after walking across the lawn. To time watering properly, look for the area of the lawn that shows water stress first. Water the entire lawn when that area begins to show symptoms. Here is a pro tip for understanding how much water is in your soil. Get the longest screwdriver from your toolbox and use that as a soil probe. Grasping the handle, you can quickly determine how much moisture is in the ground by pushing the head of the screwdriver down into the soil. Moist soil will allow the screwdriver to pass readily. Dry soil will be much harder to push through (and perhaps none at all).
A good goal when watering is to get soil moist to a depth of six inches. A lawn that is watered deeply should generally be able to go a week between waterings. Shallow watering produces weak, shallow-rooted grass that is more susceptible to drought stress. Early morning is by far the best time to water. Wind and temperatures are usually the lowest of the day, and water pressure is generally good. That allows water to be applied evenly and with little loss from evaporation. Furthermore, watering when the grass is already wet with dew reduces the chance for fungal problems to take hold of vegetation that remains wet for too long. Watering late in the evening or at night causes leaves to remain wet for an extended period, which increases the chance for disease. In fact, if you ever wanted to “cause a fungal disease problem,” just water lightly every afternoon in addition to giving it too much fertilizer.
So how does a homeowner determine how to wet their soil to a depth of six inches? Soil type, sprinkler style and water pressure determine how much water is needed to wet the soil to that proper depth and how long a sprinkler must run. Use the following steps to determine how long to run your sprinkler or irrigation system. First, set five to six open-top cans randomly on the lawn (cans with short sides such as tuna or cat food cans work best). Then turn the sprinkler on for 30 minutes. Next, measure and record the depth of water caught in each individual can. Then calculate the average depth of water from all the cans. Let us say, as an example, the average for a half hour was half an inch of water. Now get your shovel, a garden spade, or some soil probe, such as the screwdriver, to determine how deeply the soil was moistened during the 30-minute time. The probe will easily push through wet soil but less easily into dry areas. From the amount of water that was applied in the 30-minute cycle and the depth that it wet the soil, you can then determine how long the sprinkler must run to wet the soil to a depth of six inches. If you have heavy clay, it will be difficult to irrigate six inches deep as it may end up running off. Never, ever apply water to the point of run-off. Water that runs off finds its way to storm drains or running down a ditch. This not only wastes a precious resource but spends your money needlessly. If a sprinkler applies water faster than the soil can absorb it, stop irrigating until the surface dries and then resume watering.
Let us not get trapped into thinking one irrigation system is the best. There are many different irrigation systems available. Whether you choose an above ground or underground system, it is important that it is working properly. A routine check should be made to ensure that water is being applied where it is needed, in the amount that it is needed, and in a uniform manner. Use the can method, mentioned earlier, to check the distribution and amount of water being applied, and then make any needed adjustments.