Quote from Lee Garden Ninja on 23rd October 2023, 8:12 am

Hi @joanna-louise

Thanks for the pictures and comments. The mounds of soil are no bother, they're just earthworm casts and a sign of good soil health, so don't panic over those.

What causes grass to die off?

There are two probable causes looking at your pictures. The first is that there's too much shade there for that grass type. What I'd advise is choosing a shade-tolerant grass seed mix for those areas that will thrive in shadier, damper conditions.

🛒 You can view shade tolerant grass seed here.

The second issue may be chafer grubs. I've since written two full guides on this, one on how to get rid of leatherjackets and one on how to get rid of chafer grubs, which walk through telling the two apart, the right nematode species for each, and the treatment window you need to hit.

How do I know if they're chafer grubs?

Lift a flap of damaged turf with a spade and look at what's in the top few centimetres. A chafer grub curls into a firm C shape the moment you turn it out, and it has a hard orange brown head with three pairs of legs behind it. The body is creamy white and plump, with a darker swollen rear end. If instead the grub stays straight, has no legs at all and no head you can point to, that's a leatherjacket and it needs a different treatment entirely.

In UK lawns the culprit is almost always the garden chafer, Phyllopertha horticola, a small beetle with a metallic green head that flies at dusk in May and June. The Welsh chafer, Hoplia philanthus, turns up too, mostly on lighter free draining soils. Both are treated the same way.

What damage do chafer grubs do?

They feed on grass roots, which weakens the turf and stops it taking up water and nutrients, so you get brown, dying patches. The affected areas go spongy underfoot and lift away easily, and in a bad year you can roll the turf back like a loose carpet. Grass that's already struggling with shade or drought suffers far more, because it has less root system to lose in the first place.

The secondary damage is often worse than the grubs themselves. Badgers, foxes, crows and magpies will tear a lawn apart overnight to get at them, and that mess is usually what brings people to the forum. Worth knowing the animals are a symptom rather than the cause, so deterring them just leaves the grubs eating roots out of sight.

What to do about them

The only effective control left to UK gardeners is nematodes, and the species for chafer grubs is Heterorhabditis bacteriophora, sold as chafer grub killer. Apply it between late July and September while the soil is above 12 degrees Celsius, water it in, and keep the lawn moist for a fortnight afterwards. Spring applications don't work, because by then the grubs have moved deeper to pupate.

Alongside that, feed the grass properly and aerate if the ground is compacted, since a thick, deep rooted lawn tolerates a grub population that would strip a thin one bare. Once the population is down, overseed the damaged patches in early autumn or mid spring.

I hope that helps?

Lee Garden Ninja

Quote from ZoeC on 12th February 2025, 9:03 am

Hi Joanna,

My grass is very similar to yours - only 18 months old and dying in damp and shady areas. 
Did you manage to solve the problem with yours?

If so it would give me hope! It really is distressing to see it dying in front of my eyes ☹️

Thanks so much