Garden Advice

Weed Killer – How Long Does It Take to Work?

Enough is enough – it’s time to rid your garden of weeds! You put on your gardening boots and a pair of rubber gloves, and you get to spraying. A job well done, you say, and wait for the effects to show. A few days pass and… nothing! You may be asking yourself “why aren’t the weeds dead yet”? Or perhaps “how long does weed killer take to work”?

Well, the answer differs, depending on multiple factors. However, in general, it will take about 2-4 weeks for the weeds to die out completely.

Table of Contents:

So, if you:

  • Are struggling with weeds overtaking your garden;
  • Are wondering how weed killers function;
  • Want to know how long they take to work,

Then read on! This article will answer your questions.

How do weed killers work?

Herbicides are used specifically to rid your garden or crop field of weeds and unwanted vegetation, such as dandelions, moss and clovers. Most of them will either entirely destroy or severely damage the plant they’re trying to get rid of. Some weed killers target only specific weeds, while others kill everything they come in contact with.

There are several different types of herbicides and each of them works in a different way.

Types of weed killers

  • Contact. This type of herbicide is applied to living, green weeds. It gets absorbed by the plant’s leaves and is most effective when the weed is actively growing and taking in sunlight. Contact weed killers should be applied early in the day, so that they have enough time to get absorbed by the leaves before nightfall. Most useful when tackling annual weeds, this herbicide takes about 2 weeks to work.
  • Systemic. Most herbicides on the market are systemic. This kind of product can be taken in by any part of the plant – roots, leaves, etc. – and makes its way through its transport system, killing every part of the unwanted vegetation. The systemic, selective weed killer 2,4-D (for 2,4-Dichlorophenoxyacetic acid) is especially effective when tackling clovers. These products are also a good choice when dealing with perennial weeds.
  • Residual. These types of weed killers, also referred to as soil acting, are only suitable for areas such as paths and patios. What they do is poison the soil, preventing any seeds from germinating and growing in it. They can stay in the ground for months, so using them in an area where you plan to grow other plants is not advisable.

Herbicides can also be one of the following two types:

  • Selective – as the name suggests, this herbicide only targets a specific kind of plant. Weed and feed products are examples of selective weed killers, getting rid of broadleaf plants without harming your lawn in the process.
  • Non-selective – the popular weed killer Roundup is an example of a non-selective herbicide. This type kills any vegetation it comes in contact with. When using this kind of weed killer, you must take great care and protect any nearby plants you wish to keep.

How long does weed killer take to work?

The amount of time herbicides take to work will vary, depending on the weeds, the type of weed killer and the conditions under which it is applied. In general, they take 2 to 4 weeks to completely rid your garden of the unwanted plants.

If using Roundup, you may notice the first signs 6 hours in, with the leaves turning yellow and wilting. However, it will still take the herbicide around 2 weeks to fully kill the weed.

To maximise its effects, you should apply weed killers under the right conditions. Avoid spraying weeds when it’s rainy – the herbicide will be washed away and you won’t get the desired results. Windy weather is also not ideal, as the weed killer can get blown onto nearby plants you may want to keep.

Have weeds attacked your garden?

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  • There are several types of herbicides, all serving a different purpose.
  • Systemic weed killers are the most common option.
  • In general, herbicides take about 2 to 4 weeks to fully work.
  • Take extra care when using non-selective weed killers around plants you wish to keep.


Did you find this article helpful? Do you have any further questions about weed killers? Let us know in the comments below!

Image source: shutterstock / FrankHH

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