Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont
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
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
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.
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