This is the best time to use nematodes on a lawn if you want to protect it from leatherjackets

Nematodes are hugely effective at keeping pests at bay, and they can even protect your lawn from damage – but knowing when to use nematodes on a lawn will ensure they strike at exactly the right time.

It’s worth learning how to use nematodes if you’re after a natural method for banishing pests, whether in the garden or the greenhouse. Teaming up with natural predators is one of the best ways to get rid of leatherjackets in a lawn, especially as they’re rife at this time of the year.

If you’re wondering when to use nematodes on a lawn, and how they work, you’ll find everything you need to know below...

Signs you should use nematodes on your lawn

In a nutshell, nematodes are a type of biological control that works by invading the bodies of the target pests. Once the pests die, the nematodes reproduce and continue on their hunt for other pests in the soil. Because they’re microscopic organisms, you usually water them onto the lawn.

There are various types of nematodes, each targeting a specific pest, but for lawns, Nemasys Leatherjacket Killer Nematodes (which you can buy from Amazon) are the most popular.

Leatherjackets are a type of garden plant pest that can damage lawns, vegetable roots and certain plants. More specifically, they’re the larvae of crane flies.

Luckily, there are a few tell-tale signs that leatherjackets are wreaking havoc on your lawn.

‘If you’ve spotted patches of thinning grass, birds pecking at the ground, or other signs of leatherjacket activity, beneficial nematodes could be the answer,’ says Scott Brandreth, director at Gardening Naturally.

‘These microscopic worms are a natural, chemical-free way to tackle lawn pests like crane fly larvae, but timing is everything if you want them to work effectively.’

So, what is the best time to use them?

When to use nematodes on a lawn

If you want your nematodes to work effectively, you’ll need to use them at the right stage in the leatherjackets’ life cycle.

‘For most lawns, the ideal window is late summer into early autumn (late August through September),’ says Scott. ‘This is when leatherjacket grubs are newly hatched, close to the surface, and at their most vulnerable. Soil temperatures are usually still warm enough (above 10 °C), giving nematodes the perfect conditions to get to work.’

That means we’re in exactly the right spot to be using nematodes on a lawn – and releasing them into the soil now could nip any long-term damage in the bud.

August and September are also brilliant times to overseed a lawn, thanks to the warmer soil.

If you miss the boat, though, you can use nematodes on a lawn next spring.

‘In some cases, a spring treatment may also be worthwhile if you’ve had ongoing pest problems,’ Scott explains. ‘As long as the soil is moist and warm enough, nematodes can establish and help keep populations down before peak feeding season.’

Whenever you apply your nematodes, you’ll need to make sure you’re using them at the right time of day, too. Bright midday sun should be avoided at all costs.

‘UV light and dry conditions can harm nematodes on contact,’ Scott warns. ‘For best results, always apply in the early morning or late afternoon, when it’s cooler and less sunny.’

You’ll also need to avoid using nematodes at certain times of the year, especially during temperature highs and lows in winter, early spring and the height of summer.

‘Cold or frozen soils make nematodes inactive,’ says Scott. ‘They simply won’t work if soil temperatures are below 10°C.

‘Excessive soil warmth, on the other hand, can kill or stress them before they take effect.’

So, the sweet spot is between late August and September. If you’re thinking about using nematodes on your lawn this year, here’s what you’ll need:

• Nematodes, like Nemasys Natural Leatherjacket Killer Nematodes, £17.99 at Amazon
• A watering can with a coarse rose, like this Gardening Naturally Watering Can for Nematodes, £12.99 at Amazon

And that's it! Nematodes can be game-changing in the fight against leatherjackets and a range of other garden pests – and if you use them at the right time, you could stop an invasion before it starts.