Water Conservation Tips for Irrigating Lawns

Penn State's Center for Turf Grass Science estimates that lawn grass covers approximately 2 million acres in Pennsylvania which is nearly the same amount as corn and soybeans combined. Most of this grass is made up of cool season species like Kentucky Blue Grass, Rye Grass and Fescue varieties that grow best in the spring and fall when temperatures are under 80 degrees. During peak summer heat, especially when conditions are dry, grass growth slows, and the plants enter a state of semi dormancy. When this happens, the plants reduce the energy that goes into their shoots and leaves to keep alive their crown and root structures. Semi dormant grass turns brown and may look dead, but like an animal hibernating in the winter, it's just conserving its energy reserves until favorable weather returns. Semi dormant grass can survive 3 – 6 weeks in this condition before dying. If you're not sure if your grass is dead or dormant grab a handful and give a gentle tug. If the plants break loose, they were probably dead. But if they hold tight, they are probably still alive and will green up again when cooler, wetter conditions return in fall.

The good news is that brown, dormant grass does not require water to survive all but the longest dry spells. Since keeping a brown lawn green can easily require thousands of gallons of water weekly, the easiest way to conserve resources when watering your lawn is to not water at all, let it turn brown and then wait patiently for rain to return. If you follow this strategy, keep in mind that dry grass is vulnerable to structural damage if crushed, so avoid walking or driving on your lawn when it's brown if you can. By not watering your lawn you will save time, energy (especially if you are on a private water supply with your own pump) and lots of water.

If you decide to irrigate your summer lawn to keep it looking green for aesthetic reasons, withstand foot traffic from outdoor activities, or to help it survive a prolonged drought, here are some tips to minimize water use:

1. How much? Just like in an agricultural setting, there are many factors that determine how much water a lawn needs in summer including soil type. Sandy soils hold less water and dry out more quickly than silty or clay soils, or thin soils over shallow bedrock. A general rule of thumb for lawn irrigation is to apply between one and two inches or water a week, less the total of any rain that fell in the prior seven days. To keep a summer lawn green you need to add enough water to reach the grass roots, around three to six inches deep. You can see if a one inch irrigation is enough by digging a small, six inch deep test hole several hours after you finish irrigating to check for moist soil.
2. Calibrate your lawn sprinkler! A common method for determining how long it takes a lawn sprinkler to lay down enough water is to randomly scatter several small flat containers like tuna cans under the spray zone and record how many minutes it takes at full pressure for them to fill to 1-2 inches.
3. Time of day? Morning is considered best, before hot temperatures and afternoon winds increase evaporation rates. Evening watering is next best but regular nighttime watering may increase the risk of some lawn diseases.
4. How often? Allowing your soil to dry out slightly between watering may encourage deeper root growth, which may lead to healthier, more resilient turf. So the expert advice is to water deeply but infrequently during droughts.
5. Avoid runoff! If you start to see irrigation water ponding or washing off your lawn as runoff, either back off your water pressure until the runoff stops or shut off the water and resume the next morning.
6. Skip the fertilizer! Since a brown lawn is not growing very much, it does not require additional nutrients. Nitrogen applied to a semi dormant lawn is more likely to leach into groundwater or exit your lawn as runoff when rain finally does return.

Lawn irrigation done in a way that minimizes water use is not as simple as turning on the sprinkler on for an hour.

For more information see: Principles of Turfgrass Irrigation