The heat of the summer is here and your lawn is starting to look a bit different. If you’re not careful drought stress could reverse all that hard work you put into making your lawn the envy of the neighborhood. Water is the go-to answer for handling drought stress but it’s not always the only answer. Drought stress obviously causes aesthetic problems with your lawn but can also cause economic problems as well, causing you to spend money on corrective services to repair damage to your lawn. If the lawn damage of drought stress occurs year after year then your lawn is stuck in a roller coaster of ups and downs of fighting a thinning lawn with reoccurring weeds. Drought stress can occur in localized dry spots consisting of small areas of a lawn to entire lawns.

Why lawns get drought stressed

Temperature and Rainfall

Our grasses in Michigan are cool season grasses that grow best at 60 to 75 degrees. Drought stress typically occurs during periods of hot dry weather with temperatures above 80 and rainfall below a half inch per week for prolonged periods.  Commonly this can occur from June thru September and could last a week to more than a few months. Some years have limited to no drought stress while others have long periods of drought stress.

Salts

Drought stress isn’t always temperature dependent. Areas that receive high amounts of salt from winter ice melting practices can become sodic due to high salinity levels and can show symptoms of drought stress throughout the year. Fertilizers, just like ice melt products, are salts which can cause drought stress if improperly applied or not watered in with a half inch of water following application.

Compact soils

Compact soils can cause rain and supplemental irrigation to run off instead of infiltrating into the soil where it is needed causing drought stress.  Compact soil can even become hydrophobic and repel water during times of drought stress causing even more run off.

Soil Temperature

On a typical 80-degree day it seems like your cool season grass should be pretty happy but daily average temperatures are given at 4 to 5 ft above ground level. Since the suns heat energy is absorbed by the earth’s surface and radiates up, surface temperatures can average 10 to 40 degrees more than air temperatures in the summer. It is not uncommon for your lawns surface temperature to be above 100 degrees on an 80-degree day. Run a lawnmower over that 100-degree lawn and it can spike to 115 to 120 degrees instantly.

How to tell if your lawn is getting drought stressed

Thinning lawn with increased weeds

A thinning lawn with an increase in weeds can be a good indicator of drought stress. Grass plants under drought stress will shed older leaves, reduce the size of cells, as well as fold leaves in half or a V-shape to reduce the amount of light on the leaf surface giving the plants a smaller appearance.  Given the average residential lawn contains millions of individual grass plants that when smaller do not stop the sunlight from hitting the soil. This increases the soil temperature and sunlight to weed seeds, both of which will increase weed populations in the lawn.  It is not herbicide that keeps weeds out of your lawn, it is a thick uniform stand of grass that chokes off any weeds trying to grow. If your lawn has problems each year with weeds it is very likely drought stress induced.

Potassium

If you walk on your lawn and it sounds like you’re walking on potato chips it’s a good chance your lawn is drought stressed and Potassium deficient. Crunchy grass is a good indicator of potassium deficiency in lawns. Potassium is used by the plant to manage stress, disease resistance, and to regulate water within the plant. It is the second most abundant nutrient in turfgrass tissue, and if it’s low it’s going to let you know quickly in the form of drought stress, disease, and dying grass blades.

A soil test is suggested if you believe you have low potassium levels. Potassium soil levels of 275 pounds per acre should be maintained to avoid drought stress. If your soil test shows potassium in parts per million (ppm) multiply that number by 2 to convert to pounds (lbs). Potassium is used by the plant to manage stress, drought, and disease.

Lawn Color

Another good indicator of drought stress is lawn color. The green color in plants is used to attract red and blue light to create food. During drought stress the last thing the grass plant wants to do is attract more sunlight and waste resources it doesn’t need to during its dormant stage. This causes the lawn to turn a light brown color.

Sample watering

Watering a small area of lawn thoroughly and checking back in a few days can give you an idea of whether your lawn is suffering from drought stress or some other condition. Remember to water at least 1 inch deep which is .62 gallons per square foot.

What you can do to reduce or correct drought stress

Watering

Proper cultural practices can reduce or stop drought stress before it occurs and proper watering is the most important cultural practice to combat drought stress. Plants need water to absorb nutrients, complete the process of photosynthesis, and to decrease high soil temperatures. 

Proper soil moisture is the key to limiting your lawns chances of drought stress. Water your lawn with 1 inch of water per week to maintain proper soil moisture levels during drought conditions. If you are watering by hand 1 inch of water is about half a gallon per square foot. For automatic irrigation systems large sprinkler heads that rotate as they water should run 2.5 hrs per week, and small stationary heads that don’t rotate as they water should run for 45 minutes per week during drought conditions. Breaking these time periods into multiple days is more efficient based on your soil type. Clay soils hold water better and can be watered less frequently and sandy soils hold less water and may need to be watered more often.

Syringing

A practice very common in the golf and sod industry can lower soil temps quickly and is among the cheaper cultural practices for dealing with drought stress. Simply run your sprinkler system on each zone for 2 minutes during the middle of the day.  Our cool season grasses grow best in spring and fall during cool mild conditions. Simulating these conditions is important to reduce the possibility of drought stress and syringing can lower the temperature of the soil surface quickly during a critical time of the day.

Mowing

Mowing should be done during the cooler times of the day as mowing can increase surface soil temperatures quickly as well as causing water loss from the cut blades of grass. Mowing blades should be sharp to reduce the surface area affected by cutting the leaf blade. Smaller wound = faster healing. Maintaining a higher cut of 2.5 to 3 inches during the hot summer months will also help the grass plants maintain a lower temperature by increasing soil shade.

Grass species and cultivar

Genetics plays a large role in the biotic potential and health of all living things and some cultivars of our common lawn grasses just have bad genetics when it comes to handling drought. Many newer genetic cultivars have been breed for drought tolerance as well superior color and a slower growth rate. These newer cultivars can be over seeded into your existing lawn in Spring or Fall to increase your lawns resistance to yearly drought stress.

Soil aeration

The typical lawn soil in a southeast Michigan lawn is not great. The developer more than likely stripped the topsoil when your home was built and sold it off, leaving you with a subsoil high in clay as a root zone mix for your lawn grass. These soils absorb water very slowly at an average rate of .2 inches an hour, but are great at holding water in reserve if applied correctly. They also tend have low organic matter, soil microbe levels, and the roots have trouble growing deep to find water and nutrients. Aerating your lawn at least once a year can help rebuild your soil and alleviate the above problems.