During a heatwave, many people take out their lawnmowers at the worst possible time of day. Mowing during certain hours can be enough to cause your lawn to turn yellow beyond repair.
Stop Mowing Your Lawn Too Short: Landscapers’ Secret to Keeping Grass Green During a Heatwave
The temperature is soaring, shutters are closed to keep homes cool, yet lawnmowers continue to roar in the middle of the afternoon. Many people take advantage of the warm weather to tidy up their gardens and mow their lawns during a heatwave, without realizing the damage they may be causing.
According to the French National Union of Landscape Companies (UNEP), mowing at the wrong time can quickly turn a healthy green lawn into a dry, straw-like carpet.
The problem is not just the heat itself, but the exact moment the mower blades cut the grass. When grass is already suffering from water stress, cutting it too short removes its last line of defense. In as little as two days, the lawn can turn yellow, become hard underfoot, and appear dead. Fortunately, this outcome can be avoided by following a few simple rules.
Heatwave: The Mowing Hours That Can Burn Your Lawn
According to UNEP, the rule during periods of extreme heat is simple: never mow between 10 a.m. and 7 p.m.
This broad time window corresponds to the hours when the sun is strongest and the soil is retaining the greatest amount of accumulated heat. Freshly cut grass blades have little chance to recover properly under these conditions.
Instead, mowing should be done during the cooler parts of the day—early in the morning or late in the evening, ideally after 7 p.m. when temperatures have genuinely started to fall.
The goal is to give the lawn several hours to recover after being cut, allowing the grass to heal and rehydrate before facing the next day’s sunshine. Without this recovery period, every mowing session increases the risk of drying out the lawn.
Why Mowing in the Middle of the Day Can Turn Your Lawn Yellow Within 48 Hours
Each blade of grass acts as both a small water reservoir and a natural sunshade for the soil. When you mow very short grass during intense heat, you suddenly remove that protective cover.
The base of the plant becomes exposed, the soil heats up more quickly, and the fresh cuts create openings through which water evaporates. The already thirsty plant essentially loses what little moisture it has left.
Under these conditions, yellowing can appear in less than 48 hours—first as brown patches and then as fully scorched areas.
A lawn left undisturbed during a heatwave may enter a state of dormancy: it can yellow evenly while remaining alive for several weeks. In contrast, a lawn cut very short on a hot Saturday around 11 a.m. before a barbecue could resemble a dry doormat by Monday, with surface roots damaged by the heat.
The Right Approach During a Heatwave: Higher Cuts, Less Frequent Mowing, and Letting Nature Help
If mowing is absolutely necessary, raise the mower blade significantly. The recommended cutting height is 6 to 8 centimeters (2.4 to 3.1 inches) instead of the 3 to 4 centimeters (1.2 to 1.6 inches) commonly used in spring.
Experts also recommend the “one-third rule”: never remove more than one-third of the grass height in a single mowing session, and space mowing sessions two to three weeks apart.
Another often-overlooked strategy is to accept a slightly wilder lawn. White clover and dandelions, thanks to their deep roots, can draw moisture up from deeper soil layers and help neighboring grass survive. Taller grass also shades the soil, lowers ground temperatures, and protects roots.
While this less uniform look may not appeal to everyone, it helps prepare the garden for future heatwaves and periods of drought.
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