Helping lawns deal with drought

With a changing climate, droughts seem to be getting more frequent and sometimes of a longer duration.  Proper mowing, watering, and fertilizing are some of the strategies you can use to help a lawn deal with droughts and to survive.

During periods of intense heat or drought, lawns will go dormant.  They’re still alive, just not growing, so won’t need mowing.  Signs of dormant grasses, or those going into drought stress, include wilting (folded and rolled grass blades), a color change to bluish or gray green then eventually browning, and footprints visible after walking on a lawn. This is what grasses do when faced with drought or heat stress; it’s natural and normal.  So as much as you may want a green lawn all the time, go with nature and “embrace the brown”.

Having a good soil rich with organic matter will help keep a lawn growing longer, before going dormant, and to recover more quickly.  Such organic matter promotes better root growth and holds onto more moisture for the roots.  Mowing properly, and leaving grass clippings, is the easiest way to increase soil organic matter and to recycle nutrients. While topdressing an existing lawn with a light layer of compost helps, with a new lawn you can enrich the soil prior to sowing seeds or laying sod.

Deep, infrequent watering (if not provided by rain) is best to promote deep roots, which are better able to withstand drought stress.  The rule of thumb is to make sure lawns are getting an inch of water a week, if not from rain then from you.  If no rain, then apply this inch over one or two waterings a week—a good soaking each time—and preferably in the morning.  If watered in the evening, grasses stay wet into and through the night, making them better targets for insects and diseases.

Once cool-season grasses go dormant, though, it is better to leave them that way, tempting as it is to water to green them up.  Repeated growing and then going dormant drains their reserves, making them less vigorous.  This, in turn, makes them more susceptible to diseases and more prone to weed invasions.  Even though a dormant lawn, too, is prone to weed invasions, unless you can afford the time and money to water it properly it is best left dormant.

During a prolonged drought, if you can, you may want to ensure that a lawn gets one-half inch of water every two weeks.  This is regarded as a minimum to keep the crown and roots alive so that, when conditions improve, they can resume growth.  Turf will thin out and die if insufficient rain or water for four to six weeks. Once sufficient rains return, grasses will resume growth within a couple of weeks.  You only may need to water areas that are particularly stressed, such as on slopes or near heat-reflective walls, or key areas such as near a walk or patio.

Watering, in part, will depend on factors such as water cost (if on a public supply), any water restrictions, and availability (if a home well).  Use a rain gauge (available from most hardware or home stores, or better ones online) to determine how much water a lawn actually is receiving.  Showery and cloudy weather can be deceiving, as it may appear lawns are getting a lot more water than they are.

Keep in mind when watering, especially during windy and hot weather in midday, that up to half the water from an overhead sprinkler may be lost to evaporation.  Watering between 4AM and 9AM will minimize this evaporation.  A rain gauge will help ensure your sprinklers are placed so they distribute water evenly.  For narrow lawn areas, consider using a soaker hose.  You may use a timer so you don’t forget to turn off sprinklers, but make sure not to just use them on a regular programmed mode whether water is needed or not.

Mowing as high as possible helps with drought stress, too.  The amount of top growth often correlates to the amount of root growth.  So a tall lawn generally has deeper roots, which help grasses dry out less readily.  Lawns that are mainly Kentucky bluegrass should be mowed 2.5 to 3-inches high, even up to 4-inches which is the top setting for many mowers.  An additional benefit for tall grasses is that they help shade the soil, helping to conserve moisture.

Mow infrequently; really only if a lawn is growing.  I have parts of my lawn that, due to different grasses or soil conditions, grow faster than others.  So I may need to mow these areas that have actively growing grass, and not those parts that are dormant.  When assessing whether or not to mow, I want to ensure that I won’t remove more than one-third of the leaf blades at any one mowing. Also make sure mower blades are sharp so they cut cleanly.

Make note of areas of a lawn to go dormant first, as these may have underlying issues that need correcting when growth resumes—clay or compacted soil (in my case a very gravelly and non-organic soil), thatch layers (dead and living plant material between the soil and living grass parts), high pH, or poor fertility.  A soil test (kits available from many garden stores and your state Extension offices) will determine if fertility or pH (soil acidity) need correcting, and how.  Thatch, if present, comes from too much water and fertilizer, not from grass clippings if you mow properly.  You can rent a dethatcher if needed, once lawns resume growth.

Avoid fertilizing lawns when they are dormant, as under drought stress.  Nitrogen, in particular, will foster new growth which the plants can’t support when water is limited.  Applying an organic fertilizer early in the season provides fertility through the season, and avoids excesses of nitrogen.  When rains resume and growth resumes, particularly during cooler weather in early fall, is a good time to fertilize if using a non-organic fertilizer.

Obviously, limiting foot or other traffic (mowers, carts, cars) on lawns when they are dormant or stressed will help minimize damage to them.  If you’re putting in a new lawn, and drought or really hot weather is becoming more normal in your area, consider grass species (even cultivars of some like fescues) that are more drought tolerant.

Drought periods also are a good time to rethink how much lawn you really need.  Perhaps you can get by with less, substituting large areas of groundcovers where you don’t need to play or walk.  There are many choices for shady areas where lawns have a hard time growing anyway.  A wildflower patch for pollinators might be a win-win solution for a sunny area—less lawn for you to mow and maintain, and plants to support bees and butterflies.  Or, merely consider mowing less—only the edges and parts usually traveled, leaving the others for mowing once or twice a season.

Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont

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