If you take one action for your lawn this month, raise the cutting height. As the weather warms and rain becomes less reliable, the most useful thing you can do is stop cutting your grass short. A lawn held at 6 to 8cm (about 2.5 to 3 inches) through summer stays green far longer in a dry spell than one scalped to 2cm (under 1 inch), and the reason sits in the biology of the grass plant rather than in any bottle or bag you can buy. Cut too low in June and you are setting up the brown, patchy lawn that so many people end up with by mid July.
Why Short Grass Browns First in a Dry Spell
Grass manufactures its energy through photosynthesis, and that process happens in the green leaf blade, mostly in the upper portion. When you remove more than a third of the blade in a single cut, you strip away a large share of the plant’s food factory at once. The plant cannot photosynthesise enough to feed itself, so it pulls reserves out of the roots to push out new leaf. Turfgrass scientists at the University of Minnesota and Ohio State University have shown that removing more than one third of the leaf surface in one mowing can halt root growth for days while the plant rebuilds its canopy. Repeat that week after week and the root system stops reaching downward.
Root depth is exactly what carries a lawn through a dry summer. Deep roots reach moisture that sits well below the surface, so a lawn with a strong root system can stay green for weeks without rain. A scalped lawn with a shallow, stunted root system runs out of water within days because there is nothing tapping the reserves lower in the soil. Longer grass also shades the soil surface. A taller canopy keeps the ground noticeably cooler and slows evaporation, so the moisture that is there lasts longer. Cut the grass to 2cm and you expose bare soil to direct sun, the surface bakes, and the little water present evaporates fast.
There is a second danger in cutting too low, called scalping. When the mower removes leaf right down to the crown and the woody stem base, you damage the part of the plant that regenerates new growth. Scalped patches turn straw coloured within a day or two because there is almost no green tissue left, and the bare, weakened turf opens gaps that weed seeds and moss are quick to fill. What looks like a tidy short cut in June becomes a thin, weed dotted lawn by August.
The Right Height for Your Lawn in Summer
The correct summer height depends on the type of lawn you have. A general family or utility lawn made up of ryegrass and fescue is best held at 6 to 8cm (about 2.5 to 3 inches) once the warm, dry weather sets in, rather than the 2.5 to 4cm (1 to 1.5 inches) you might keep it at in spring and autumn. A fine ornamental lawn of bent and fescue can be kept lower, but even there you should raise the height by 5 to 10mm above the spring setting during summer stress. The principle is the same at every level: the hotter and drier it gets, the higher you leave the grass.
Apply the one third rule alongside the height setting. Never take off more than a third of the total blade in one pass. If your lawn is sitting at 9cm and you want it at 6cm, that is a third removed and it is fine. If it has run away to 12cm because you skipped a week, drop it to 8cm first, then bring it down to 6cm a few days later. Trying to take a long lawn straight down to summer height in one cut is itself a form of scalping. Through the warmest part of summer you may only need to mow once a week or even less, because cool season grasses slow their growth when soil moisture is short. Let the grass tell you when to cut rather than mowing to a fixed calendar.
Most modern rotary mowers make height changes easy. A machine such as the Bosch Rotak range adjusts from roughly 20mm to 70mm through a single lever (around £150/$190), so moving up for summer takes seconds. Cylinder mowers, common on fine lawns, are adjusted at the rollers and are worth setting higher for the season as well. Whatever you own, find the height settings before you start and pick the highest one you are comfortable with for the look you want. You can always lower it again in September when the weather cools and growth picks back up.
How to Raise the Cut Without Shocking the Grass
If your lawn has been kept short and you want to bring it up for summer, do it over two or three cuts rather than all at once. Grass that has grown used to a low cut has its leaf and energy concentrated near the base. Letting it grow taller in stages gives the plant time to build leaf area higher up and adjust. Raise the mower by one notch, cut, wait several days, then raise it again until you reach your summer height.
A sharp blade counts for more as you raise the height, because taller, softer summer grass tears easily. A blunt rotary blade bruises and shreds the leaf tips instead of slicing them, leaving ragged wounds that lose moisture and turn white at the tips within a day. Those frayed ends also let in disease. Sharpen a rotary blade or have it done at the start of summer, and check it again midseason. Mow when the grass is dry, ideally in the cooler part of the morning or the evening, never in the full heat of midday when cutting adds stress to a plant already losing water. Leave the clippings on the lawn during dry weather if your mower mulches, because a light scatter of fine clippings returns moisture and nitrogen to the soil as it breaks down.
The Mistakes That Undo a Higher Cut
The most common error is giving the lawn a short cut just before going away, on the theory that it will not need mowing for a fortnight. In summer that short cut is the worst possible state to leave a lawn in, because the scalped grass has no canopy to shade the soil and no leaf to feed the roots while you are gone. You return to brown patches that take weeks to recover. If you are away, leave the grass longer, not shorter.
Another mistake is watering little and often to compensate for a low cut. Light daily sprinkling wets only the top centimetre of soil and trains roots to stay shallow, which is the opposite of what you want in a dry summer. A taller lawn watered deeply but rarely, around 2.5cm (1 inch) of water once a week, builds the deep roots that keep it green. Finally, do not panic if a higher lawn looks a little shaggy. A summer lawn at 7cm that stays green and dense is healthier, and easier to keep that way, than a closely shaved one that browns at the first hot week and spends the rest of the season recovering. Get the height right now and the lawn largely looks after itself through the heat.
It helps to know what the grass is doing under the soil while all this plays out. Cool season grasses such as ryegrass, fescue and bent put on most of their root growth in the cooler shoulders of the year, then draw on that stored root mass to survive summer. A lawn that was scalped repeatedly through spring entered June with a weaker root system than it should have, which is why some lawns brown within days of the first hot spell while a neighbour’s stays green. You cannot rebuild roots overnight, but raising the cut immediately stops the daily drain on what reserves remain, and that alone is often enough to hold a lawn together until autumn, when deeper repair work like aeration and overseeding becomes worthwhile again.
