When to use weedkiller on a lawn – the ideal window for cracking down on weeds is almost here

Spring is here, and it’s the perfect time to start prepping our lawns for summer – and knowing when to use weedkiller on a lawn will give your chance the best chance of thriving.

Figuring out how to get rid of weeds in a lawn is no easy feat, but if you time it right, weedkiller can do a pretty good job – and alongside other lawn care tips, it’ll boost the health of your grass for the year ahead.

I’ve asked the experts when to use weedkiller on a lawn to help you schedule the task into your lawn care calendar – and it’s sooner than you’d think.

Where to buy weedkiller for lawns

Whichever weedkiller you go for, always read the label first – while many products are safe for grass, they won't be safe for pets and children, so make sure you follow the instructions carefully.

Above all else, the key to tackling weeds with weedkiller is waiting until they’re actually growing.

‘The ideal time to apply a weedkiller is when weeds are actively growing, typically between May and October,’ says Chris McIlroy, lawn expert at The Grass People.

The science behind it? ‘Treating weeds during this period ensures that the herbicide is effectively absorbed and transported to the root system, preventing regrowth,’ explains Cheryl Harper, managing director at Greensleeves.

So, you’ll need to wait just a little while longer for the best results – but it’s also a good idea to keep one eye on the weather forecast.

‘Avoid strong sunshine and wet conditions, as you want the product to stay on the weed’s surface long enough to be absorbed,’ advises Chris.

In fact, drought conditions should be avoided as much as wet weather. ‘Avoid applying herbicides during very hot or drought conditions, as stressed plants may not absorb the treatment effectively,’ explains Cheryl.

‘A dry, calm day with no rain expected for at least 24 hours is ideal,’ says Cheryl.

So, that solves it: while you can learn how to scarify a lawn this month, the best time to use weedkiller on a lawn is during the growing season, ideally from mid-spring to summer, when the weeds are most likely to absorb it effectively. Just make sure you watch out for any particularly wet or dry weather.

FAQs

Is it okay to spray weeds before rain?

If you’ll be using weedkiller on your lawn, you’ll want as little to go to waste as possible – and that means using it at the right time.

‘I wouldn’t advise applying weed treatment when rain is forecasted, as the product could wash away before it’s had a chance to get to work on the problem area,’ says lawn expert Chris from The Grass People.

‘Most weedkillers need at least four hours to get to work, so as long as you have a rain-free period, your treatment should be effective.’

Is it better to spray weeds before or after mowing?

You might also be wondering when to use weedkiller on a lawn if you’ve recently started cutting your grass again after winter.

‘It’s best to spray weeds before mowing because the herbicide needs to be absorbed through the leaves to effectively reach and kill the root system,’ explains Cheryl from Greensleeves. ‘When weeds have a full, healthy leaf surface, they can take in more of the weed control, making the treatment much more effective.’

You should also wait for a few days after applying the weedkiller to mow again to ensure it has enough time to work its magic.

It might be a little too early to use weedkiller on your lawn, but you can still get cracking with plenty of other garden jobs in April this weekend.