One of the most common questions regarding lawn irrigation is, “How long should I water?” I never have a quick and easy answer to the question, since no two lawns are exactly alike in terms of rooting depth, soil type, soil condition and irrigation system.

When watering your lawn, your goal should be to wet the soil where grass roots are growing, no more and no less. Most turfgrass roots extend 4 to 6 inches into the soil, but some may penetrate to 12 inches or more. Generally, you should wet the top 6 inches of the soil thoroughly. Deeper root systems take in water from a greater soil volume, so lawns with deep roots can be watered less often than lawns with shallow root systems. If water is being applied properly, cool season grasses such as tall fescue, Kentucky bluegrass and perennial ryegrass should grow well on two to three deep irrigations a week.

Many gardeners rely on a time clock to tell when the lawn needs water. A better way, at least initially, is to check for soil moisture in the root zone using a shovel, hand trowel or soil probe. If the soil at six inches deep feels moist, the grass does not need water yet. Or, you can check for moisture by simply pushing a screwdriver into the soil at various locations in your lawn. You will be able to push the screwdriver into moist soil easily; but, the screwdriver will stop when it hits dry soil.

Watering a lawn thoroughly enough to wet the soil at least six inches deep is often easier said than done. Most sprinkler systems apply water much faster than the soil can absorb it. As a result the water simply runs off, especially on mounded or sloped landscapes. You will never be able to water your lawn efficiently and effectively until you can control runoff. To do so may require turning off your sprinklers for one or two hours to let the water soak in before continuing the irrigation. Repeat this cycle until the soil is wet to the proper depth.

In order to avoid runoff, you may need to correct some common water penetration problems. The two most common problems are thatch accumulation and soil compaction. Thatch, which restricts water, air and nutrient movement into the root zone, is undecomposed organic matter that builds up between the leaf blades and the soil surface. You should remove thatch in spring or fall by vertical mowing or by hand raking. Soil compaction also restricts air, water and nutrient entry and slows root development. The best way to relieve such compaction is by aerifying (coring) the soil. You may rent lawn aerifying equipment, or have the work done for you by a lawn maintenance professional.

Remember, the length of time needed to water you lawn adequately is determined by the time it takes to wet the soil as deep as the roots are growing, at least six inches. Grasses and soils differ, so your irrigation schedule must be tailored to your lawn. It’s not uncommon to run the sprinklers for 1/2 hour or longer at each watering to wet the soil adequately.