Managing Grass Quality During High Temperatures And The Recovery Process

The past four weeks have seen temperatures in many parts of the UK reach record levels for June and July, with areas of Gloucestershire having temperatures in excess of 30 degrees. With this in mind, please find below some information and tips to help your lawn.

What happens when the grass plant becomes stressed due to excessive heat and how can we respond?

• Grass has the ability to go dormant during adverse weather conditions. Dormancy is simply a state of reduced water usage where the grass plant focuses its resources on protecting the roots. 
• Summer dormancy is a normal response of the grass plant to the stress of high temperature, and while dormant grasses may turn off colour at times, they will recover when conditions improve. Most grass plants can stay in a dormant state for at least 4 weeks without the grass leaf being damaged, so there is no need to be over concerned, even given the high temperatures recorded recently.
• The length of dormancy depends on the genetics of the species and the overall health of the grass plant. Grasses to include ryegrasses and strong creeping red fescues having the ability to withstand the high temperatures along with having the ability to recover sooner. The way that we manage the grass plant when conditions are in our favour, and the balanced application of nutrients we apply, really does have an effect on the quality of the plant when it is under stress.

What can we do to assist grass quality and recovery?

• Watering - While watering will re-hydrate the grasses, it is important to apply enough water in wetting the soil profile to a minimum depth of 150mm, and even more important to apply water in the cooler periods of the day, if the moisture applied is not to be lost through evaporation. This will keep the plant active as the roots search for the moisture and the nutrients available, allowing increased photosynthesis and chlorophyll production, which will maintain the leaf colour for longer.
• Mowing - Mow the grass at the top end of the recommended height range (30-35mm). To further minimise stress, mow only when needed, and during the cooler periods of the day. A sharp mowing blade is also vital as the higher the temperature the greater the moisture lost from the leaf of the plant. A sharp cut will reduce the level of moisture lost, vitally important in maintaining the quality of the grass leaf during high temperatures.
• Fertiliser - During periods of dormancy, it is wise to reduce the amount of fertiliser applied. The dormant grass will not actively process large quantities of nutrients. Excessive nitrogen applications during high temperatures can promote excessive top growth at the expense of the root (when water is applied through irrigation), with such activity causing damage to the plant, so while there may be a short period of time when the application of fertiliser is reduced, as soon as the weather does break, it is important to get the nutrient down in aiding the recovery process.
• Weed Control - Some weeds such as dandelions thrive during reduced moisture levels because they have large tap roots that hold water. While a blanket application of herbicide can further stress the dormant grasses, it is possible to spot treat weeds with a selective herbicide for as long as they remain in growth, and while allowing for the lawn to remain weed free, it will also allow for the moisture still available in the soil to be used by the grass pant.
• Usage - If the grass is dormant it is not able to readily repair itself, so by reducing the traffic on the lawn as much as possible and avoiding any activity on the grass during the hottest times of the day, will again allow for the plant to withstand the high temperatures for longer, with less apparent damage to the grass leaf.
• Rehydrating the plant - All soil structures have differing capacities of moisture retention and given the recent warm and dry weather we have experienced across Gloucestershire; moisture levels are at their lowest for a number of years. Once we do get some meaningful rainfall, it would be worth looking at introducing a wetting agent as part of a treatment plan, as it will maintain moisture for longer, allowing for the plant to recover fully. Not only will this be important to the recovery and rehydration process, it will allow the plant to be healthier should we see a further period of sustained heat later in the summer. Wetting agents work only when water is available in the soil, and can be applied at differing rates of application, ranging from annually to monthly or bi-monthly. I would recommend applying the product bi-monthly for at least two applications post the drought period to action full recovery of the plant, through photosynthesis and chlorophyll production.

If you want an expert to come and complete a 14 point lawn analysis and put together a treatment plan with you to restore your lawn once the weather breaks please call 01452 223329 or email [email protected]