Just how much should you water your lawn? If you don’t worry much about this question you likely, 1) have an automated sprinkler system, 2) have cheap irrigation water you ‘just have to use’, 3) believe more is always better, and/or 4) have enough disposable income that you don’t need to think about it.
In our area, nearly two-thirds of the water used by homeowners is to maintain landscapes. Studies found that a typical homeowner applies 80 inches of water to their lawn each growing season. This is twice as much as necessary. We should not be comfortable with nearly one-third of our culinary (most likely) water being used in the over irrigation of lawns.
Our area will likely see more development pressure in coming years. While its easy to frown on this notion, moderate growth is healthy for a community. Those future homes will need water. It is likely that we won’t have the luxury of excess water most now enjoy. For now, be grateful for the water we have. Regardless of your water stewardship views, there are reasons to manage lawn water in addition to saving water.
Your lawn needs deep roots. Frequent, short irrigations develop shallow roots. Plants that don’t need to hunt a little for water won’t be resilient when summer heat comes. They will also need more fertilization as they will only have access to the nutrients in the top few inches of soil. Lawn grass should have roots 12-24 inches deep. There are often plenty of resources for the roots in the soil, but frequently watered grass has been conditioned not to grow towards them.
Nitrogen follows water. By far the most limiting nutrient in lawns is nitrogen. When you buy a fertilizer, it will have three numbers that represent nitrogen, phosphorous and potassium. The last two will stay in the soil for years depending on your management. Nitrogen however moves wherever the water does. If you over-irrigate it will be taken below the root zone. Heavily watered lawns will require more nitrogen fertilizer to keep them green and healthy.
Heavily watered lawns will have more problems. Constant soil saturation, often coupled with heavy fertilization, lends itself to fungal diseases and increased insect pest pressure. The environment created favors pests and disease, and the grass is less able to deal with the pressure.
Your irrigation schedule is heavily determined by your soil texture. A soil test is a good idea, but you should always let the grass be your guide. In June try irrigating once every three days of ½ to 1 inch of water each time. Hot July weather may require every other day for a time. If your grass shows signs of stress before the next irrigation, first try increasing the time you water each irrigation. If your soil is sandy you may need to water more frequently. Your goal should always be to lengthen the time between irrigations for maximum lawn integrity. For further guidance see: https://www.extension.uidaho.edu/publishing/pdf/CIS/CIS1157.pdf