Some time around the end of July, every lawn starts to look the same: straw yellow, dusty, with a few stubbornly green islands where the midday shade falls. And every year the same question comes up. Is the lawn ruined now, or can you just sit this out?
The short answer: you can almost always sit it out. Our lawn grasses come from a cool temperate climate. Over their history they learned to sleep through hot, dry weeks and carry on afterwards. What really harms them in summer is rarely the drought itself. It is what we do out of worry: cutting too short, sprinkling a little every evening, feeding in the middle of a heatwave.
In order, then: what happens inside the lawn when it gets hot, how high the mower needs to be, how much water actually arrives where it matters, and how to check whether anything is still alive under the straw.
At a glance
- Mowing higher is the single most effective thing you can do. From mid June · CW 24 at the latest, the mower belongs at 5 to 6 cm. If it is still set lower, raising it is your first move. Longer blades shade the soil and keep it cooler and damper.
- Water rarely, but deeply. One or two goes per week with 15 to 20 litres per square metre each time. Short and daily pulls the roots upward and makes the lawn dependent on you.
- Water early in the morning, between 4 and 8 o'clock. In the evening the blades stay wet all night, which is an open invitation to fungal disease.
- Brown is not dead. Healthy grasses survive four to six weeks of summer dormancy and start growing again after the first proper rain.
- Do not fertilise, scarify or oversow while it is hot and dry. The window for oversowing opens from mid August · CW 33, the potassium-rich autumn feed from mid September · CW 38.
What happens in the lawn when it gets hot
Almost every lawn seed mix you can buy in Germany contains the same three species: perennial ryegrass (Lolium perenne), smooth meadow grass (Poa pratensis) and red fescue (Festuca rubra). All three come from a cool temperate climate; the technical term is cool season grasses. Their growth optimum sits at roughly 15 to 25 degrees. Once the thermometer climbs above that, they throttle back photosynthesis, and from about 30 degrees they stop putting on length altogether.
Add drought to the heat and they switch into summer dormancy. The plant withdraws from its leaves, gives them up, and concentrates everything on the growing point right down at the base. That is the small, firm spot from which new blades will come later. The material above ground turns to straw, but the growing point stays alive.
How long that works depends on the soil. A sandy soil is empty after a good week without rain in summer heat; a loamy one holds out for two to three weeks. And it depends on rooting depth. That is where it is decided whether summer becomes a problem for your lawn, and you set it up in spring.
Mowing higher works immediately
There is no single measure that does as much in summer as one notch higher on the mower. A lawn 6 cm tall shades its own soil. Underneath it stays measurably cooler and damper, water evaporates more slowly, and weed seeds get no light to germinate.
Closely shorn areas heat up instead. The soil lies bare in the sun, dries out on top, and the grasses are left with very little leaf area to feed themselves from. The lawns that looked most immaculate in June are the first to turn brown in August.
Choosing the cutting height for your situation
There is no single number that fits everyone. What matters is sun, soil type and how much foot traffic the area gets.
Cutting height in high summer
- Sunny utility lawn · 5 to 6 cm
The standard for the area you play and sit on. Two notches higher than in spring. It looks a little softer and less severe, but it lasts considerably longer.
- Sandy or shallow soil · 6 to 7 cm
Where water drains away quickly, every centimetre of shade counts. Go one notch higher still here and mow less often in exchange.
- Shade lawn under trees · 7 to 8 cm
In shade the grasses compete with tree roots for water and have little light. They need every blade just to make enough sugar.
- Ornamental lawn · not below 4 cm
Even if you want the English look, give a little ground in high summer. Below 4 cm July and August get very tight for these grasses.
On top of that comes the one third rule, and in summer it applies more strictly than usual: never take off more than a third of the blade height at once. Cutting a 12 cm lawn down to 5 cm in one pass tears the plant out of its own supply line in the middle of the heat. Two passes three to four days apart are gentler, even though it means doing the job twice.
Mulch mowing pays off in summer
The fine clippings stay on the surface, do not evaporate straight away, and return moisture and nutrients to the sward. The condition is that you mow often enough for the clippings to stay short. On a lawn that has been left to grow long once, a thick mulch layer smothers the grasses instead.
Watering: rarely, but right through
The most common summer mistake is not too little water. It is too little water at a time, every single day.
If you sprinkle for ten minutes in the evening, perhaps 3 to 4 litres per square metre arrive. That soaks in two or three centimetres deep and evaporates again the next morning. The grasses learn from this to keep their roots up high, where that small amount of water reaches. After a few weeks you have a lawn with roots in the top five centimetres that wilts after two dry days.
Turn it around and it works. One large dose, applied rarely, pulls the roots downward.
Work out the amount
Reckon on 15 to 20 litres per square metre per watering. That equals 15 to 20 mm of rainfall and wets the soil to a depth of roughly 10 to 15 cm. On 100 m² that comes to 1,500 to 2,000 litres, which is five to ten fillings of a water butt holding 200 to 300 litres.
Measure it with the tin test
Put three or four flat tins inside the sprinkler's circle, empty tuna tins work well. When 15 to 20 mm have collected, the dose is complete. Time it once while you are at it, and you will know for the rest of the summer how long your sprinkler needs to run.
Run it early in the morning
Between 4 and 8 o'clock evaporation is at its lowest and the blades dry off over the course of the morning. In the evening the leaf stays wet all night, and that is exactly what fungal diseases such as red thread are waiting for.
Repeat once or twice a week
In heat above 30 degrees and on sandy soil, twice; otherwise once is enough. Between doses the surface is allowed to dry out. That is intentional.
Watch for puddles
If the water runs off or stands on the surface, the soil is compacted or the dose came down too fast. In that case water in two portions with half an hour in between.
Decide first, then stick with it
Watering and letting the lawn go dormant are both fine choices. What really stresses the grass is switching: two weeks of sprinkling, then two weeks of nothing, then sprinkling again. Each time the plant pushes out new growth and burns through reserves. Decide at the start of the dry spell which way you are going. There is more on water quantities across the whole garden in watering wisely in summer.
Anyone watering regularly should also keep an eye on where the water comes from. Drinking water for the lawn is expensive, and in dry summers some municipalities restrict garden watering by public order. A water butt or cistern will at least cover the smaller areas.
Watering properly once is worth more than seven times a little.
The summer rule for lawns
Brown is not dead: how to check
Before you start sprinkling out of worry, or reseed the whole area straight away, do two simple tests.
The pull test. Take hold of a tuft of blades and pull gently. If the plants stay firmly rooted, the base is intact and the lawn is only sleeping. If they come out with a light tug and the base is brown and soft, that patch really has died.
The base check. Part the straw with your fingers and look right down at the base of the blades. A living growing point is firm and has a pale, slightly greenish core. A dead one is strawy all the way through.
If your lawn passes the test, waiting is enough in a normal dry spell. After the first soaking rain it takes about two to three weeks for the area to turn green across the whole surface. First single green tips appear, then the sward closes up.
If the drought drags on beyond four weeks, give an emergency dose of 10 to 15 litres per square metre every two to three weeks. The area stays brown, but the growing points survive. And expect the ryegrass in particular to drop out after a very long dormancy, while meadow grass and red fescue come back. You close those gaps with an oversow in late summer.
Keep off a dormant lawn
The growing points are brittle while the grass is dormant. Walking across a bone dry area for weeks, driving the mower over it or leaving the paddling pool standing on it breaks them off. Those are exactly the spots that stay bare after the rain. So reroute the shortcuts across your summer lawn, or lay stepping stones.
What to leave well alone in summer
Three well-meant measures do more harm than good in the heat.
Applying nitrogen. A nitrogen-rich fertiliser drives soft, thirsty growth at precisely the moment the plant has no water. On top of that there is the risk of scorch when granules sit on dry soil. The summer feed belongs around CW 24 and only on an area that is still well supplied. After that you wait for the autumn dose. The full rhythm is in feeding your lawn through the year.
Scarifying. A scarifier tears the sward open and exposes bare soil. At 30 degrees that is an open wound which dries out and invites weed seeds in. The right dates are April and early September, not high summer. The why and how is in scarifying against moss.
Oversowing. Lawn seed needs two to three weeks of evenly moist soil to germinate. In July you only manage that with daily watering, and even then the seedlings scorch easily. The good window opens from around CW 33, when the nights get cooler and the soil is still warm. Until then, simply make a note of the bare patches and read up in peace on oversowing bare patches.
Clover in the lawn is a summer advantage
What counts as a weed in spring rescues the look of the lawn in August. White clover roots deeper than the grasses, stays green when everything else has gone strawy, and gathers nitrogen through root nodule bacteria that the grasses benefit from too.
Daisies and low growing thyme also take heat better than a pure grass sward. If you can live with them, you get the greener surface in high summer and do the bees a favour on the side.
If that idea appeals to you, the next step is not a better lawn fertiliser but a different kind of surface. A herb or flowering lawn copes with drought in a completely different way, and converting lawn into a flower meadow can be tried out on part of the area first.
When it is not just the drought
Sometimes there is more behind brown patches than missing rain. These patterns are worth a second look.
Irregular, merging straw yellow patches point to a fungus. Red thread (Laetisaria fuciformis) shows pink red threads on the blade tips in damp weather and mainly attacks undernourished areas short of nitrogen. It usually clears up on its own once the area gets nitrogen again, so with the starter feed that goes with oversowing from CW 33. Sharply defined, coin sized circles suggest dollar spot instead.
The sward lifts like a carpet and underneath there are whitish, curled larvae: those are chafer grubs, usually from the garden chafer. They eat the roots directly beneath the sward, often in August and September. Birds, crows or badgers tearing the area open are another giveaway.
Yellow brown rings or half circles that grow larger year after year are fairy rings. The fungus in the soil makes the ground water repellent, which is why the patch stays dry despite watering. The only things that help here are slow, deep soaking with a wetting agent, or breaking the soil open mechanically.
Do not simply reseed after grub damage
If the sward lifts off, the roots are gone. New seed on the same spot gets eaten just the same. Deal with the larvae first, then repair, or you will do the job twice. Apply the right nematodes (Heterorhabditis bacteriophora) between July and September, once the soil is warmer than 12 degrees. Water the area thoroughly beforehand, apply in the evening because the nematodes are sensitive to UV light, and keep the soil moist for about two weeks afterwards. On a bone dry summer lawn they will not work.
The plan for the rest of the summer
From now into autumn
- Until mid August · CW 33
Mow high, mow less often, and water thoroughly once or twice a week if needed. Do not fertilise, do not scarify, and simply make a note of bare patches.
- CW 33 to 37
The best window for oversowing. The soil is still warm, the nights are getting cooler, and rain is falling again. Mow the area short first and rough the patches up lightly.
- From CW 38
The autumn feed with potassium. It makes the grasses frost hardy and is the most important dose of the year. Bring the cutting height slowly back down to 4 to 5 cm.
- CW 44 to 46
The last cut before winter, once growth has stopped. Clear the leaves off so the sward keeps its light.
And then there is the quietest part of all this. A lawn is a project measured in years. The summer in which you first managed to accept that the area turned brown is the summer in which the roots went deeper. If you note in your garden journal when you watered and how long your lawn held out without rain, you will know fairly precisely next July when the time has come. That is worth more than any rule of thumb from the internet.
Common questions about lawns in summer
How often should I water the lawn in summer?
Once or twice a week is enough, but with 15 to 20 litres per square metre each time. In heat above 30 degrees and on sandy soil, lean towards twice; on loamy soil once will do. Brief daily sprinkling is worse than not watering at all, because it keeps the roots up near the surface.
What is the best time of day to water a lawn?
Early in the morning, between 4 and 8 o'clock. That is when the least water evaporates, and the blades dry off during the morning. A lawn watered in the evening stays wet all night, which encourages fungal disease. Sprinkling at midday in full sun mostly wastes water.
My lawn has gone completely brown. Is it dead?
Usually not. Pull on a tuft: if it sits firm, the plant is alive and only dormant. Healthy grasses survive four to six weeks of summer dormancy. After the first proper rain it takes two to three weeks for the area to green up again. If the tuft comes out easily and the base is brown and soft, that patch really has died and needs oversowing in late summer.
How high should I mow the lawn in summer?
At 5 to 6 cm, and in shade under trees even 7 to 8 cm. That is one to two notches higher than in spring. Longer blades shade the soil, keep it cooler and damper, and slow down germinating weed seeds. Never take off more than a third of the blade height at once.
Can I fertilise the lawn in high summer?
Better not. Nitrogen drives soft growth that immediately needs more water, and granules on dry soil can scorch the blades. The summer dose belongs around CW 24 and only on an area that is still adequately supplied. After that you wait for the potassium-rich autumn feed from CW 38.
When can I reseed bare patches?
From roughly CW 33 to CW 37, so mid August to mid September. By then the soil is still warm enough for quick germination and the nights are getting damper. In July lawn seed only germinates with daily watering, and the seedlings scorch easily.
Sources and further reading
- Watering wisely in summer with the quantities for beds, containers and shrubs
- Feeding your lawn through the year with the three doses and their dates
- Oversowing bare patches for the late summer window
- Scarifying against moss with the right dates in spring and autumn
- A climate resilient garden in drought and heavy rain as the wider picture
- Plant profiles in our database: white clover, daisy, thyme
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