When is the best time to spray weed killer? Garden experts reveal how to get effective, long-lasting results

Have weeds been slowly taking over your garden throughout winter and early spring? To fight them off effectively, the garden experts have shared the best time to use weed-killing spray and why timing matters.

Weeding is always a dreaded task when it comes to sorting the garden out, and one we often put off altogether if we can. But if you're not taking part in the rewilding trend, then you'll probably want to banish weeds from your garden for good, and finding the most effective long-term way to do that is key.

Although the concept of weeding is rather simple, some conditions can make it pack more of a punch, one being the timing with which you use weed killer spray, which is why we've called on the gardening experts to give us the full rundown.

When is the best time to spray weed killer?

Whilst there are several ways to get rid of weeds in your garden, for a long-lasting, effective result, there are some conditions you'll want to keep in mind. One of these is when you apply the weed killer.

"Depending on the type of weed killer you are applying will dictate when the best time of year is to use it, although you would be wasting most types of weed killer if you applied it when weeds are dormant, typically late autumn to late winter, as weeds need to be actively growing to absorb the weed killer so that it can take effect," starts Lucie Bradley, gardening expert at LBS Horticulture.

"The only weed killer which you should apply before weeds appear is pre-emergent weedkillers, as these are designed to kill newly sprouted seeds before they reach the surface of the soil, so these are applied in early spring when the soil is getting warm enough for seeds to begin germinating," she continues.

For a truly effective application, you should be adding your weed-killing duties to your essential summer gardening jobs to-do list.

"When using a contact weed killer, developed to rapidly kill any parts of the weeds it comes into contact with, then you are best to apply these during the summer (June to August) when weeds are actively growing. The warmer, sunny days speed up weed growth and at the same time increase the rate of the contact weed killer being absorbed into the foliage," adds Lucie.

"If you are using a systemic weed killer which is designed to be absorbed through the leaves of weeds but then is distributed throughout the whole of the weeds, effectively killing the roots as well as the foliage, then you can start applying these from late spring through to early autumn, with the best time being late spring as this is when weeds are rapidly growing so the weedkiller is quickly transported down to the roots," she recommends.

Lucie Bradley

With over 28 years working in the garden industry, Lucie has been fortunate enough to spend every day speaking to both amateur and professional gardeners. Encouraged to garden since she was old enough to walk, she believes that you can never know everything about gardening, as it is constantly evolving.

Is it better to apply weed killer in the morning or evening?

In the same way there's a best time of day to water your lawn in the summer, weed killer spray is most effective during one specific time of day.

"The best time of the day to apply weed killer is around mid to late morning. This is because any dew on the plant should have dried out, and the heat of the sun will not be too intense, as high heat can make the weed killer evaporate before it can work," says Richard Barker, horticulture expert and Commercial Director at LBS Horticulture.

Avoid making a summer gardening mistake and don't leave your weed killer spraying until too late in the day.

Richard Barker

With 4 years in the industry, Richard is keen to share his knowledge with both experienced and beginner gardeners, and prides himself on keeping up to date with the latest horticultural trends.

FAQs

Should I cut weeds before spraying?

If you've decided not to keep your wildlife-friendly weeds growing, you might want to get them removed as soon as possible. So much so, you may want to cut the leaves off them, but this isn't always the best idea.

"The aim when applying both contact or systemic weed killers is that it is applied to the foliage of the weeds, so the more foliage there is, the faster it will be absorbed, so cutting back the weeds first would reduce the foliage and actually reduce the effectiveness of the weedkiller. So it’s best to spray the weeds and wait for the weed killer to be able to work before removing the dead foliage," suggests Lucie.

"The only exception to the no cut rule is when you have weeds which have been able to become well established, so they are tall, sturdier, possibly ‘woody’and have tough, leathery leaves. In this case, you are best to trim the weeds back and allow them to start regrowing before applying a weedkiller, as it will be absorbed faster and be more effective on the fresh new growth," she continues.

For these established weeds, or weeds that are in and amongst your favourite plants, having the essential gardening tools to remove them manually is the better method.

When should you not spray weeds?

Weeds growing in just about every spot in your garden, sometimes even in between your favourite late summer flowers, this is when you will want to refrain from spraying weed killer. You'll also need to consider the weather conditions.

"You should not spray weeds if it is windy, as this can risk the herbicide drifting to nearby plants. Similarly, you should not spray weeds when it is raining, as the herbicide is likely to be washed off. It is also best to avoid spraying weed killer during very hot weather, as the heat can slow plant metabolism and reduce the effectiveness of the weed killer," begins Richard.

"If weeds are struggling due to drought, it is unlikely that they will be able to absorb weed killer, and weeds that are dormant or not actively growing will also not absorb herbicides as successfully," he finishes.

It can be discouraging coming back to your garden after winter and seeing that the frost didn't kill all the weeds. But dealing with them sooner rather than later will stop their spread and leave your garden looking lush just in time for summer.