The cool, rainy weather in April and May was ideal for the cool season turfgrasses. As we move from spring to summer, temperatures rise and the rains typically become less frequent. Growing conditions become less favorable and turfgrass growth slows. Hot, dry weather can cause considerable stress for the cool season grasses. However, proper care during stressful periods can help to maintain a healthy, good quality lawn.
Sound mowing practices are necessary for good quality turf. This is especially true during the summer months. Improper mowing during hot, dry weather may seriously damage the cool season grasses.
Mow Kentucky bluegrass lawns at a height of 3 to 3 1/2 inches during the summer months. During cool weather in spring and fall, bluegrass lawns should be mowed at a height of 2 1/2 to 3 inches. The additional leaf area during summer shades and cools the crowns of the turfgrass plants. Extremely high temperatures at crown level can kill turfgrass. Raising the mowing height during the summer months also discourages turf diseases, such as summer patch.
When mowing the lawn never remove more than one-third of the total leaf area at any one time. A lawn mowed at a height of 3 inches should be cut when it reaches a height of 4 1/2 inches. Removing more than one-third of the leaf area weakens the turfgrass and reduces its capacity to withstand additional environmental stresses. Weakened turf is also more likely to be invaded by weeds.
If possible, mow in the cool of the morning or evening. Mowing during high temperatures of midday places additional stress on the turf. Also make sure the mower blade is sharp. Dull blades tear and bruise the leaf tips.
Gardeners have two basic options on lawn care when confronted with hot, dry weather. One option is to simply allow the turf to turn brown and go dormant. The alternative is to properly water the lawn to maintain green turf during dry weather.
Kentucky bluegrass lawns survive extended periods of drought by going dormant. Most healthy lawns can survive in a dormant state for 4 to 6 weeks without rainfall or irrigation. Healthy lawns that have been allowed to go dormant will green up again when the turf receives sufficient water.
Gardeners who want a green lawn throughout the summer should water the lawn when symptoms of moisture stress begin to develop but before the grass becomes dormant. A good indicator of water stress in turfgrass is leaf color. The normally green leaves become a dull blue- green. Additionally, water-stressed turfgrass is less resilient. Footprints remain in the turf after walking across it.
Turfgrass requires approximately 1 to 1 1/2 inches of water per week. The actual amount of water required depends upon the soil type and weather conditions. When irrigating turfgrass, the general rule of thumb is to water deeply but infrequently. A thorough soaking (which moistens the soil to a depth of 8 to 10 inches) once a week is much better than frequent, light applications. Watering deeply promotes the development of deep root systems. Deeply-rooted turfgrass can withstand stressful weather conditions much better than shallow-rooted plants.
The best time to water a lawn is early morning. Winds are generally light and temperatures cool so little water is lost through evaporation. Watering at midday is less efficient because large amounts of water are lost through evaporation and strong winds may cause uneven water distribution. Strong midday winds may also carry the water onto driveways and streets and waste considerable amounts of water. Watering the lawn in the evening or at night may increase disease problems.
Individuals wishing to establish a new lawn should prepare the site this summer. The best time to seed lawns in Iowa is mid-August through September. Late summer is also an excellent time to overseed thin lawns.
As summer fades to fall, the cool season grasses will again have more favorable growing conditions. Good lawn care this summer will minimize stress and keep the turfgrass in good condition.
This article originally appeared in the June 11, 1999 issue, p. 76.
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