This spring’s cool, wet weather has helped with recovery of lawns that were damaged by last year’s drought. Although no one knows for certain what kind of weather is in store for summer, the National Weather Service forecasts abnormally warm temperatures for the Mid-Atlantic region. It’s also possible we will be experiencing periodic dry conditions, so lawn enthusiasts should be ready for anything.

Summer Dormancy

Most lawns in Pennsylvania are composed of turfgrasses that grow best in the cool, moist conditions of spring and fall. Although these grasses often struggle during summer, they are equipped to withstand limited periods of high temperatures and dry conditions, provided they have been properly managed and do not receive a lot of physical abuse. One of the main survival mechanisms turfgrasses use to endure summer stress periods is summer dormancy.

Summer dormancy of turfgrasses involves slowing or cessation of leaf growth, loss of green color, or in advanced stages, complete dieback of older leaves and stems. This is a natural process triggered by gradually increasing temperatures and lengthening daylight. In practical terms, the grass plant is going into protection mode to avoid severe desiccation and death by restricting its use of water, energy, and other internal resources that ordinarily go into producing green grass leaves. The dormancy process preserves the important growing center at the base of the plant so that growth can resume when cool, moist conditions return. In most years, dormant (or semi-dormant) turfgrasses recover from summer stress, even though they appear brown and dried out in mid-summer.

Dealing with Lawns During Hot, Dry Periods in Summer

When lawns are experiencing extended periods of hot, dry weather, good cultural practices can reduce turfgrass injury and facilitate recovery when favorable conditions return.

• Mowing: Avoid mowing when grass is brown and not growing, or when it is wilting (turning blueish gray). If you must mow during hot, dry periods, do so in the morning or evening when temperatures are cooler. Also, keep your mowing height at around 3 inches and make sure mower blades are sharp and properly adjusted. Traffic: Limit the amount of traffic and/or any type of aggressive maintenance practices like dethatching or aeration on stressed, wilting, or dormant lawns. Trampling dormant turf can injure the growing points and limit recovery when cool temperatures and moisture return.
• Irrigation: Watering lawns on a regular basis in the summer is expensive and often not necessary. If you decide to water, be sure to wet the soil deep enough to reach most of the turfgrass roots. Check soil moisture with a trowel or other type of probe to see if water has penetrated to the desired depth (this should help reduce the frequency of watering). Water should be applied in the morning, especially on hot, windy days. Night watering can sometimes promote disease activity on warm, humid evenings.
• Fertilizer practices: Fertilizer practices can sometimes influence how turf responds to summer heat and drought. Potassium is important in restricting water loss in plants, so timely potash applications can help turf conserve water during drought conditions. Whereas nitrogen is important for maintaining growth and green color, too much nitrogen in the heat of summer can make turfgrasses susceptible to drought and warm- weather diseases.

What if Wet Conditions Persist?

Although some rain is a welcome respite in summer, too much rain can encourage common lawn diseases such as red thread and dollar spot. More destructive diseases, such as brown patch, gray leaf spot, or Pythium blight can occur when high temperatures combine with humid/wet weather during the summer months. In such cases, fungicides may be warranted as a control measure.

Keep in mind that disease-causing pathogens are always present in lawns but are dormant most of the year. Diseases only occur when environmental and cultural conditions favor pathogen activity on a susceptible plant.

Grub Problems

Attempts to control grubs with insecticides when they are feeding on turfgrass roots in late summer and fall are often ineffective. The current trend in grub control is to use the insect control product, chlorantraniliprole, over the entire lawn in spring or early summer, well before grubs hatch from eggs and begin to feed on roots. The advantage of this product over other insecticides is its effectiveness, low-toxicity, and it is safe to use around bees.

Article and photos assembled by Pete Landschoot, Professor Emeritus, Penn State University