Has your lawn turned from green to brown? No need to worry, your grass has just gone dormant from the summer heat.
According to NOAA’s National Climatic Data Center, the spring of 2012 was the warmest on record in the U.S. and rainfall was 0.24″ below normal. In June, 164 all-time high temperature records were tied or broken around the country, which is unusual this early in the season – record breaking temps typically occur in July and August (see this update on record-shattering heat).
This record spring heat comes on the heels of a warm winter which was the hottest and driest that the western U.S. has ever seen. These conditions – early heat and lack of moisture – are stressful on the grasses in your lawn, which may be turning brown and appear “burnt” or “burned out” in spots.
If you’re in the upper south, parts of the midwest, pacific northwest, or northeast U.S., your lawn is most likely planted with cool season grasses like Kentucky bluegrass, perennial ryegrass, fine fescue and/or tall fescue. Cool season grasses look great in spring and fall because they thrive when daytime temperatures are in the 60-75 degree range and rainfall is normal. But during the dog days of summer, usually July and August, they become dormant until temperatures return to more favorable conditions sometime in September.
Dormancy is a survival mechanism for cool season grasses. When daytime temps consistently reach 90+, the grass re-allocates its resources to the roots and crown instead of the blades. Very little growth occurs and the grass turns brown, giving homeowners the impression their lawn is dead or diseased.
From Louisiana State University Ag Center: “Grasses have the ability to go dormant for differing lengths of time depending on their genetics, rooting and overall health. The spectrum of grass stress runs from reduced growth or some discoloration at moderately dry levels; to drier conditions where recovery is possible but plants brown out (fire up) and weaken; to deep dormancy where we see damage or death. Dormancy is simply a state of reduced metabolism and water usage where the plant focuses resources on the roots and survival. The grass will turn mostly brown and is considered unsightly – but not dead.”
You’ve probably noticed that in the winter your lawn goes dormant as well, but it takes on a somewhat different appearance than what you see now. Winter dormant lawns are consistently brown throughout, with a straw-like tone. In summer dormancy, the lawn may appear spotty or patchy – some brown here, some green over there.
Unless you water your lawn deeply every week, there is little you can do during dormancy to get your lawn green again. But there are some things you can do which may cause a great deal of damage.
Don’t mow a dormant lawn on your regular schedule
Don’t mow your lawn just because it’s Friday night and that’s when you always do it. If your lawn has put on sufficient growth of an inch or two, give it a cut. If it’s little changed from the week before, let it go. In fact, during dormancy it’s beneficial to let the lawn grow a little higher than usual, as the longer blades will provide more shade for the roots and help keep what little moisture there is from evaporating. The shading may also keep lingering weed seeds from germinating.
Don’t fertilize a dormant lawn
Do not fertilize your lawn during a dormant period. The fertilizer won’t be taken up by the water-starved roots and the fertilizer which is left to lay on your lawn may actually “burn” it, leaving you with bigger problems to fix in the fall.
Watering a dormant lawn
The key to keeping your summer lawn from going from dormant to dead is water: Dormant grass will die if the crowns, roots and rhizomes dehydrate.
But there’s no need to water dormant grass unless you’ve gone without significant rainfall for at least four weeks. Dormant grass can survive up to six weeks without water, depending on the air temperatures and soil condition.
From Ohio State University Extension: “… a light watering or rainfall of 1/2 inch every two to three weeks will help minimize damage to the lawn during the dormancy period. This watering practice will supply enough moisture to keep crowns, rhizomes and roots hydrated and alive. This volume of water will not regreen a dormant lawn, however, it will help to insure good recovery once rainfall occurs later in the summer. “
Your goal during dormancy is to keep the roots and crowns from dehydrating and dying. Water early in the morning while grass is already wet from dew, temperatures are cooler, humidity is high and wind is calm. These conditions favor the infiltration of water into the soil.
Dry soils have difficulty absorbing water, so to minimize runoff, water for thirty minutes, turn off your sprinkler, then resume watering thirty minutes later. Once the soil is wet, more water will be able to infiltrate it, minimizing runoff. Runoff occurs when your irrigation rate (how fast you’re watering the lawn) exceeds the soil’s infiltration rate (how fast your soil can absorb the water).
From Healthy Lawns, Clean Water: “Measure your soil’s infiltration rate by cutting off both ends of a coffee can and inserting it several inches into the soil. Pour about 1 inch of water into the can and time how long it takes to soak in. Then measure your irrigation rate by placing a coffee can (with the bottom intact) in the area watered by your sprinkler and time how long it takes to fill the can with 1 inch of water. Your irrigation rate should not exceed your infiltration rate.”
Weeding dormant lawns
Unfortunately, some lawn weeds love the heat and will thrive during your lawn’s dormancy with help from their large taproots. In order to keep them from taking over your lawn when the cool temps return, pull them by hand, making sure your remove the taproot as well.
Don’t play on dormant lawns
Encourage your kids to play in a public park, or better yet, send them to a swimming pool. Heavy traffic on an already stressed, dormant lawn may damage the grass beyond repair and compact the soil.
When the summer heat gives way to cooler temperatures and regular rainfall, your lawn will be restored to its former glory. Have patience.