Lawns
Why is my lawn turning yellow? The causes and the fixes
Most yellow lawns are drought, dog urine, too much fertiliser or grubs eating the roots. The pattern tells you which: irregular patches in dry weather, round patches with a dark green rim, stripes after feeding, or turf that lifts like a carpet.
Read the pattern first
Yellow and brown patches have a handful of common causes, and each leaves a recognisable signature. Looking closely before buying anything saves treating the wrong problem.
| What you see | Likely cause |
|---|---|
| Irregular brown areas in a dry spell, most marked on sandy soil or over tree roots | Drought |
| Round dead patches with a bright green ring | Dog urine |
| Stripes or blotches days after feeding or weedkilling | Fertiliser or chemical scorch |
| Yellow patches that lift like a loose carpet; birds pecking the lawn | Leatherjackets |
| Yellowing in autumn, turf torn up by crows, badgers or foxes | Chafer grubs |
| Patches with a reddish tinge and pink threads in late summer | Red thread |
| Small yellow patches turning brown with white fluff at the edges | Fusarium patch |
Drought and scorch
Brown grass in a dry summer is the most common cause by far, and usually the least serious. The Royal Horticultural Society describes drought browning as usually temporary: the grass goes dormant and recovers once rain returns. Its advice is not to water an established lawn in summer however brown it gets, but to mow less often, raise the cutting height and leave the clippings on the surface as a mulch. Weedkiller and fertiliser should wait until spring on a lawn that has been through a drought.
Scorch looks similar but follows the spreader. Brown stripes or blotches appearing a few days after feeding mean too much fertiliser landed in those strips, and the same happens with weedkillers and moss killers applied too heavily. Following the stated dose, applying before rain or watering it in, and walking the spreader in straight overlapping lines prevents it. Scalped bumps where the mower cuts to the soil, and spills of petrol or oil, leave patches of their own.
Dog urine
Urine patches are circular and dead in the middle, with a ring of unusually lush, dark green grass around the edge, where the diluted nitrogen acts as a feed. Female dogs cause more of them because they empty the bladder in one place. Soaking the spot with water straight away dilutes the urine and limits the damage. Dead patches can be raked out and reseeded once the soil has been flushed through.
Grubs in the roots
Leatherjackets are the grey brown larvae of crane flies, up to 30mm long, and feed on grass roots and stem bases from February to October. Damage shows as yellowish brown patches that often die, and starlings and crows probing the lawn are a strong hint. Biological control uses microscopic nematodes, Steinernema feltiae or S. carpocapsae, watered on from September to early October as a preventive when the soil is moist and at least 12C.
Chafer grubs are fat, white, C-shaped larvae up to 18mm long. Their damage is most obvious from autumn to spring, and is often made worse by crows, magpies, badgers and foxes tearing up the turf to reach them. The nematode for chafers is Heterorhabditis bacteriophora, applied from July to September with the soil between 12 and 20C. Damaged areas are reseeded or returfed in mid to late spring.
Lawn diseases
Red thread shows as patches 7.5 to 25cm across with a reddish tinge, later bleaching to straw, and fine pinkish red threads on the leaf blades. It is most common in late summer and autumn after wet weather or heavy dews, and is linked to low nitrogen and compacted, airless soil. The RHS fix is a nitrogen feed such as sulphate of ammonia at 15g a square metre, not applied after August, along with scarifying, aerating and boxing off the clippings.
Fusarium patch, also called snow mould, starts as small yellowish patches that turn brown and can spread to 30cm or more, with white or pinkish cottony growth at the edges in damp weather. It is most common from autumn to spring and under lying snow, and is encouraged by lush nitrogen rich growth late in the year. Better drainage and aeration, brushing dew off in the morning and avoiding high nitrogen feeds in late summer and autumn are the controls. No fungicides for lawns are available to home gardeners.
Repairs and when to call someone in
Small patches can be raked out, topped with a little fresh soil and reseeded in spring or early autumn. Larger damaged areas are quicker to returf. A lawn treatment visit costs £30 to £70 and can diagnose and treat grubs or disease, and turf supplied and laid runs £10 to £30 a square metre where a patch is too big to seed. A lawn that yellows in the same place every year is worth digging into: buried rubble, a shallow layer of builder's sand or an old path can sit a few centimetres under the grass.
Common questions
Will a yellow lawn recover on its own?
After drought, almost always, once rain returns. Patches killed by urine, scorch, grubs or disease usually need raking out and reseeding or returfing.
Should I water a brown lawn in summer?
The RHS advises against watering established lawns in summer, because the grass recovers when rain returns. Save water for new turf and newly sown areas.
How do I know if I have leatherjackets or chafer grubs?
Lift a section of damaged turf and look in the top few centimetres of soil. Leatherjackets are grey brown and legless; chafer grubs are white, curved into a C and have legs near the head.
Does lawn feed fix yellow grass?
Only where the yellowing is hunger or red thread. Feeding drought stressed, scorched or grub damaged grass does nothing, and too much feed causes scorch of its own.