When to Water: Frequency and Amount

Try to give your lawn the water it needs--and no more. This moderate approach conserves an important resource, saves money, and helps prevent grass diseases caused by too much water. How much water your lawn needs depends on the health of your lawn and soil, the amount of rainfall your lawn gets, and the climate. You may need as few as two waterings a year or as many as two a week.

The best approach to watering grass (and most other plants) is to follow nature's pattern of rainy periods followed by brief dry spells. Apply enough water all at once to penetrate to roots, let the soil almost dry out, and apply water again. Grass signals that it needs water by losing its spring: When you walk across the lawn and see your footprints, your lawn probably needs to be watered.

To determine how much water your lawn needs, you need to consider several factors: the depth of your grass roots, your soil type and its "penetrability," your irrigation method, and of course, the weather. First, check to see how deep the roots of your grass grow. Add an inch to the average root depth to arrive at a target watering depth. It makes no sense to waste water by watering to a level substantially deeper than you lawn's root zone.

Root depth depends on how much time you have taken to improve your soil and on the type of grass you are growing. Some grasses, such as tall fescues, have roots that reach one foot deep. Others grow to only half that, in even the best conditions. As your grass develops deeper roots, adjust your watering-depth target so that you continue to encourage roots to go deeper.

Next, determine how much water is needed to moisten soil to the root zone. A good rule of thumb for most grasses is one to two inches per week. If you have porous soil that drains quickly, you would apply one inch of water twice a week. Conversely, if your soil holds water well, a good guess would be 1-1/2 to 2 inches once a week.

To determine how long you should run your sprinkler to deliver the desired amount of water, wait for a four- to five-day dry spell. Then set out some empty cans in various locations on the lawn. Run your sprinkler or in-ground sprinkler system until the cans contain 1 inch of water. Then, wait twenty-four hours to allow the water to penetrate the soil (12 hours if your soil is porous--porous soil drains faster); then check the depth of the moisture penetration.

If one inch of water moistens soil to a depth well beyond the root depth, try the procedure again after your soil has dried, but turn off the sprinkler sooner. Conversely, if the root depth is not reached, try delivering more water. Keep accurate records of how long you need to run your sprinkler or sprinkler system to deliver the required amounts of water for your lawn, and then base future waterings on what you have learned from your observations.

If it rains during the week, decrease your watering by the amount of rain that fell. If it's hot and sunny or windy, you may need to increase the watering amount and frequency.