By Normand Helie and Toby Wolf
This year's extreme drought has affected landscapes throughout eastern Massachusetts. It may also be a harbinger of a more common future, as climate change alters weather patterns.
Over the summer, as the turf on Boston Common began to go dormant, many people felt alarmed by what they saw as dead grass, and pictures of the Common's turf cropped up in several newspaper articles about the drought.
How can lawns be restored from brown to green - and how can they be kept green in the future? As extreme weather becomes more common and park use increases, what are the keys to maintaining healthy lawns in urban parks?
Some of the news is good: The grass in those brown patches is dormant, not dead. Turf grasses cope with hot, dry weather by holding water in their roots rather than their leaves. They sacrifice their green top-growth, which becomes brown and brittle, to keep the roots alive, biding their time. When the weather cools and the rains return, the roots send up fresh green shoots.
Dormancy is a natural, adaptive response that helps grasses survive dry summers. By understanding these responses, we can learn to create conditions that support grass's natural resilience. Every lawn is different, but here are some general guidelines:
- Start each year with a plan: With each increase in accuracy, long-term weather forecasts have become a more important tool for planning. If summer drought is forecasted, for example, consider mowing higher [or watering deeper] during the spring so that the turf has more sugars [water] stored in its roots by the time dry weather arrives.
- Grass Loves to be Cut: Turf grass's astonishing adaptability includes its ability to grow back stronger and thicker after being mown - as long as the mowing is moderate and well-timed. If a lawn is mown too low, when the weather is too hot, or too soon after fertilization, the loss of leaf area will weaken the plant, reduce root growth, encourage weed germination, and cause premature brown-out. It is optimal to mow to a height of 3" or greater, and reduce the height of the turf by no more than 1/3 in any one mowing. Mowing should be reduced during drought, and not be performed within a week following any treatment or when the temperature is above 90 degrees. The right equipment makes a difference too: sharpened mower blades make cleaner cuts, and mulching mowers keep nutrients on site, reduce water loss, and eliminate the cost of off-site disposal.
- Irrigate in moderation: The shape of a plant's root system is often determined by the availability of water. In lawns that are irrigated daily, water is available at the surface of the soil, so roots spread horizontally. These lawns may look great in the short term, but they are entirely dependent on continued watering, and their shallow roots are vulnerable to root rot. Irrigating less often allows the soil to dry out between waterings and encourages root systems to grow deep, where moisture levels are more stable. Deep-rooted turf is less likely to develop an unhealthy thatch layer and it is better adapted to withstand drought.
- Build healthy soils: When urban soils are compacted by foot traffic and other day-to-day use, they can become impenetrable to water and air, and root growth. Deep-rooted turf can reduce soils' vulnerability to compaction, but if compaction is already present, aeration is necessary. In most cases core aeration is helpful, as a best practice measure, but under extreme stress vulnerable lawns/soils can be harmed by the aggressive nature of aerating. Always refer to your plan and be prepared to adapt to seasonal conditions.
- Feed lightly: Some soils are better suited for lawns than others, so it's tempting to try to create the "perfect" soil on every site. For any large park, however, it's more realistic to work with the soils we have, adding nutrients and minerals lightly and selectively. Observation and testing can help to understand what the soils need, and necessary products can be added. For example, timed applications of lime can mitigate acid soils and increase the availability of existing nutrients, and light treatments with Potassium can help turf and other plants survive drought by regulating their transpiration of water.
- Set realistic expectations: The mark of a healthy lawn isn't that it never browns out at all; it's that it browns out partially and briefly - for weeks, not months. Understanding dormancy as a natural adaptation, rather than a sign of failure, is essential to establishing the real-world practices that will create thriving and resilient turf.
