The dog days of summer are just around the corner. This means heat and humidity in most of the United States and Canada. This can be tough on lawns, especially lawns with cool-season grasses. Here are three tips for helping your lawns through this stressful time of the year.
1. Mowing: The cardinal rule of mowing is not to remove more than 1/3rd of the leaf tissue with any one cutting. If turfgrass is mowed often enough, the injury is minimal and the response of the plant is to tiller and produce a more prostrate growth habit, which results in improved density.
However, the natural tendency of the plant is to grow straight up, and if you wait too long before mowing then basically you are "harvesting" the leaf blades. Removing excessive amounts of tissue results in scalping and is a tremendous burden on carbohydrate reserves. In other words - don't scalp.
It is also generally recommended that the height of cut be increased to the maximum recommended for the species used. Taller turf uses more water, but the taller canopy also shades the soil surface and reduces evaporative loss from the soil. Taller-cut turf, therefore, usually conserves more water than does shorter cut turf.
Also, use a properly sharpened blade. This reduces leaf tearing and reduces water loss through cuts in the leaf blade.
2. Irrigation:To avoid problems with drought damage, either water the turf correctly or allow it to go dormant. Dormancy is how grasses deal with moisture deficits and is less harmful to the stand than sporadic watering.
If you do chose to irrigate throughout the hot summer, water deeply and infrequently (1 to 2 inches once or twice per week) and when the plant is just beginning to show signs of moisture stress.
There are two easy methods of determining moisture stress, foot printing and color. If the plant is moisture stressed it will not have turgid leaves. The result is that when you walk on the turf, your footprints will remain. Also, moisture-stressed grass takes on a bluish-gray green. The nature of this color change is similar to what happens when you roll the turf to make stripping on the field. When the leaf is moisture stressed, it begins to roll up in cross section as pictured below:
As the plants roll up, they reflect light differently than do turgid, flat leaves. That is what causes the change in appearance. Again, to avoid drought damage, commit to a regular irrigation schedule, or allow the grass to enter dormancy. Haphazard irrigation is the single worst thing you can do to the turf during the summertime.
3. Fertilization: Application timing is very important for minimizing weed encroachment in summer months. As a rule, apply fertilizer lightly in the spring and more heavily in the fall.
Heavy spring fertilization promotes leaf tissue production (at the expense of carbohydrate reserves) and diminishes the ability of plants to withstand summer stress.
Use fertilizer sparingly during the summer, and based mostly if the grass appears to be "hungry". Whether you irrigate or allow the turf to go dormant is another consideration when it comes to applying fertilizer during the summer.
A note of caution: some fertilizers have high physiological burn potential that is exacerbated by high temperatures. If, for example, you use potassium chloride (KCL) it should be applied when temperatures are below 70°F and then thoroughly watered in after application. Potassium sulfate is another option that is more expensive, but is also safer to turf.
Editor's note: Dr. David Gardner is a turf expert at The Ohio State University and serves as an editorial advisor for Turf magazine.