5 Best Fast-Acting Weed Killers That Are Strong, Yet Safe (2021 Review)

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In this guide we’ll take a look at the best weed killers for the UK market.
I’ve compared effectiveness, speed, product safety, and cost
to give you my top recommendations.

What is the Best Weed Killer?

In a rush? Here's my top choice...

Roundup Fast Action Weed Killer

Powerful, fast-acting weed killer!

This Roundup Fast Action Weed Killer is a well-renowned product for banishing weeds from the garden. It gets results in 24 - 48 hours and is easy to apply thanks to its built-in 'pressure spray' applicator. It kills most weeds with one application and the 5 L bottle will cover approximately 150 m².


Everything I Recommend

  • Very popular weed killer
  • Results in 24 - 48 hours
  • Easy pressure sprayer application
  • Fantastic weed killer
  • Results in just 24 hours!
  • Kills the weed and the root
  • Best weed killer for lawns
  • Vast coverage - over 600 m²
  • Best value for money
  • Best heavy-duty weed killer
  • Kills roots so no regrowth!
  • Won't kill your grass
  • Excellent for problematic weeds
  • Eco-friendly and biodegradable
  • Visible effect in 1 hour

More Detailed Weed Killer Reviews

Roundup Fast Action Weed Killer

  • Very popular weed killer
  • Results in 24 - 48 hours
  • Easy pressure sprayer application

Roundup Fast Action Weed Killer Review

The Roundup Fast Action Weed Killer is an incredibly fast-acting solution for unsightly weeds.

It will kill them off in 24 – 48 hours, usually with just one application.

The built-in pressure sprayer means the product is extremely easy to apply.

Plus, the design of this particular pressure sprayer feels superior to its competitors. It prevents hand fatigue thanks to its one-touch trigger system, and the wand is extendable so there’s no need to crouch or bend!

It’s up there as the easiest to use of all the weed killers.

The 5 L container will allow for 10 minutes of uninterrupted weed spraying (of course, this doesn’t all need to be done at once!)

The sheer popularity of this product shows it’s the best weed killer around. If you’re looking for a top-selling, high-performance weed killer that’s incredibly easy to use, this is the one for you!


  • Most customers report seeing results within 7 days
  • Can reach and spray weeds up to 4ft away so can be used in awkward areas
  • Leaves no harmful residue and degrades into the soil
  • Users find it easy to target specific weeds


  • Best applied immediately before heavy rain which can be difficult to judge
  • Some users have found the pump difficult to use
  • Results vary from user to user, as it doesn’t seem to be effective on all weeds
  • Larger weeds may still need to be pulled out of the ground

Resolva 24H Weed Killer

  • Fantastic weed killer
  • Results in just 24 hours!
  • Kills the weed and the root

Resolva 24H Weed Killer Review

Resolva 24h weed killer is one of the best weed killers available in the UK.

Part of its unique formula contains an active ingredient that is absorbed extremely quickly by the weed, helping it get to work straight away.

More importantly though, it kills both the weed and the root to stop them coming back.

Weeds will be seen visibly quaking after only 24 hours, and soon they’ll be killed off completely!
The built-in pressure pump is easy on the hands and can be used with either a jet or spray depending on your needs!

This 5 L bottle will treat an area of approximately 18.5 m² and contains enough product for 5 minutes of continuous spraying.

Want to see the back of those weeds in your garden and stop them returning? Kill the plant and the roots with this 24h weed killer!


  • Fast acting - many customers report seeing results within 24 hours
  • There’s no harmful residue leftover as the formula is broken down naturally
  • The large container can be refilled when empty offering better value for money
  • Comes with either a jet or spray trigger head, so targeting individual weeds is easy
  • No premixing required - can be used straight away


  • Needs to be used on a dry, sunny day which you may need to wait for
  • Doesn’t seem to be effective on all weeds
  • Although pet-safe, pets and children should still be kept away from the treated area until it has dried fully
  • Needs to be handled with care as any spillages will kill your other plants

Weedol Lawn Weed Killer

  • Best weed killer for lawns
  • Vast coverage - over 600 m²
  • Best value for money

Weedol Lawn Weed Killer Review

Killing weeds in your garden shouldn’t be a stressful task. You just need something that does the job quickly, isn’t messy, and isn’t too expensive.

Weedol Lawn Weed Killer is all of those things.

This clever formula allows you to kill weeds without affecting your grass, and it takes all of 5 minutes to apply.

Do note that it may not be right for weeds in your flowerbeds (depending on the type of plants you grow) – for this you’re probably better off with a weeding tool.

If you’re looking for the best weed killer to tidy up your lawn that won’t leave your grass crying – look no further!


  • Effectively destroys weeds without damaging your lawn
  • Has a wide coverage area, with 1L covering up to 667㎡
  • Most customers found it very easy to use, with clear instructions


  • Many users have found results are best if they scarify the lawn a few days after application
  • Customers with a lot of weeds may need to make a stronger solution
  • Won’t kill moss so a separate moss killer may need to be purchased
  • Requires premixing and a lot of care needs to be taken not to let this product touch your skin

Vitax SBK Brushwood Tough Weed Killer

  • Best heavy-duty weed killer
  • Kills roots so no regrowth!
  • Won't kill your grass

Vitax SBK Brushwood Tough Weed Killer Review

Sometimes, a project warrants something a bit more ‘heavy duty’… Enter stage left – Vitax SBK Brushwood Tough Weed Killer!

This weed killer is capable of killing brambles, nettles, thistles, dock, woodland weeds, hardwood saplings and even tree stumps.

Clearly this industrial-strength product packs quite a punch!

Interestingly though, this heavy-duty weed killer won’t kill your grass which is a rare benefit compared similarly strong solutions.

Naturally, it’s quite a potent formula, so do take care when using it, but if you’re up against a particularly unruly area, Vitax SBK will probably save you some time and heartache.

If you have a serious amount of weeds that need taking care of, this heavy-duty high-strength formula will help you tackle them into submission!


  • Very effective at killing brambles and most common weeds
  • Won’t damage your lawn
  • The bottle is well-designed with an airlock dispenser for measuring the dose
  • Can be applied using either a watering can or weed sprayer


  • Unlike others on the market, this product requires mixing before use
  • Results are slow with some customers only starting to see results after 3 weeks
  • Re-application may be needed to keep weeds at bay
  • A stronger solution is required for more stubborn weeds

Neudorff Superfast, Long Lasting Weed Killer

  • Excellent for problematic weeds
  • Eco-friendly and biodegradable
  • Visible effect in 1 hour

Neudorff Superfast, Long Lasting Weed Killer Review

Here we have a weed killer from a company that perhaps few of us have heard of, but they’re sure to become better known in the next few years – their products boast very good results.

Neudorff Superfast, Long Lasting Weed Killer works in as little as and hour, and is very good against specific, problematic weeds like goutweed, field horsetail, mosses and algae.

What I also like about this solution is its low-level toxicity. It’s less harmful to wildlife than some more aggressive weed killers. If you’re interested in doing more to help our outdoor friends, you can read my article about how we can help the declining bee population here.

Even the ethos of the company is commendable, with a commitment to producing environmentally friendly, biodegradable products using raw, sustainable materials.

In the past it has felt like the only option for killing really unruly weeds was to unleash some very powerful chemicals into the world. However, this product shows there’s another way.

Hands down this is the best weed killer if you’re looking for an eco-friendly option to tackle those more problematic weeds.


  • Very effective at killing Horsetail and other problematic weeds
  • Biodegradable and is broken down into the soil after application
  • Helps prevent the regrowth of tough weeds
  • Low toxicity to bees


  • The coverage area isn’t as impressive as others on the market, with 1L covering just 60㎡
  • Repeat application may be needed for stubborn weeds
  • The marks on the measuring cylinder are not particularly clear
  • Only dispenses enough to cover 5㎡ at any time - so time consuming for those with large gardens

Things to Know Before Buying Weed Killer

Ah dear, time to talk about every gardener’s worst nightmare…weeds!

I think we all agree that having the odd weed here and there is par for the course in the garden. However, these pesky plants can spread so rapidly, they easily have the potential to invade entire lawns and flowerbeds.

Forks, trowels and hoes are good to have in the armoury against weeds. But sometimes you need something more. An effective weed killer can help truly eliminate unwanted weeds, keeping your garden looking pristine.

The following tips will help you find the best weed killer for your garden:

There are a range of weed killers on the market.

Selective weed killers are usually safe for application on lawns and will only target a specific plant type.

Non-selective weed killers will kill any plant they come in contact with

Systemic or industrial weed killers are slower than others, but they are stronger. They have the strength to kill even resistant plants like brambles and briars. These products are absorbed into the plant itself, traveling down to the root, killing the plant from the inside out.

Residual weed killers are applied to the soil and prevent seeds from germinating.

Contact weed killers kill on contact. These often affect all plant species so need to be applied very carefully.

Natural weed killers, as the name suggests, are made from natural ingredients. While these tend to be less effective than industrial strength weed killers, they are safer to use on your lawn and kinder to wildlife.

Weed killers use herbicides to control, limit and stop plant growth.

The actual chemicals vary depending on the type and brand of weed killer. Most are safe for application around other plants, although you should always read the packaging.

Some weed killers will kill whatever plant they come into contact with, and you should also check before using them near plants you intend to consume.

Weed killers work in a variety of ways, and often use a combination of methods to banish weeds. Some of the ways they can work to kill weeds are as follows:

Stopping photosynthesis

Plants need light in order to survive and create food, a process known as photosynthesis.

Some weed killers work by stopping the plant’s ability to photosynthesise, starving the plant.

Stopping Protein Production

Protein production is another essential element of plant growth and health.

Some weed killers stop plants from being able to produce proteins. Ultimately this causes the plant to die.

Glyphosate works this way; however, do your research before using products which contain Glyphosate – is has been shown to have negative effects on health.


The plant’s hormones dictate its growth.

Some weed killers contain plant hormones that, when applied to the plant, confuse the plant’s growth system. It eventually becomes deformed and dies.

One of the first choices you’ll have to make is whether to choose a weed killer that contains glyphosate.


Glyphosate is rarely used on its own, instead mixed with other chemicals. It’s an exceptionally powerful chemical and can be toxic in large amounts. In recent years, it’s developed a reputation for being dangerous, with many gardeners now choosing to use glyphosate-free weed killers.

When using products with glyphosate, you should take adequate safety precautions. Wear clothing that covers the arms and legs, and do not touch the plants after they have just been sprayed.

If you do choose to use products with glyphosate, I highly recommend using goggles, gloves and a face mask.

Natural Weed Killers

Natural weed killers are far safer to use and kinder to the environment.

Once the weed killer has dried, you can allow pets and kids into your garden without worrying. Most natural weed killers work quickly and won’t damage the soil.

Many natural weed killers can also be used near or on plants that you are planning to consume.

Of course, you must still check the label, but in general they won’t damage the quality of your fruit and vegetables or create dangerous toxins.

All the weed killers I’ve recommended are fast-acting, often delivering results in just 24 hours.

Some products made need reapplying a few weeks later if they didn’t quite get the weeds the first time, but you’ll still notice them getting to work very quickly.

The coverage area is important to look at, as this will save you money long term.

If you have a larger garden, look for a bottle of weed killers with a larger coverage area.

A bottle concentrated formula tends to offer the best value for money but can be more fiddly to apply. You’ll need to decant these products and measure them out.

However, if you buy 5 L of concentrated solution, it be able to cover more area than 5 L of unconcentrated, ready-to-spray, product and may cost the same amount.

After treating your garden with weed killer, you’ll have a clean slate. But how can you stop the vicious cycle of weeds growing back?

Prevention is the Best Cure

Dealing with weeds can be exhausting, and when weeds start rapidly colonising your garden, prevention is certainly the best cure. Preventing weeds is a continuous process, and finding something to tackle the seeds is a good place to start.

Chemical weed killers can be great to use in this instance to stop weed seeds from germinating in the first place.

Consider Mulching

A thick layer of organic mulch can prevent weeds from taking over your garden.

This will help the soil retain moisture while also smoothing out small weeds and spoiling their environment.

Mulch will decompose and add nutrients to the soil, preventing natural light from reaching the weeds.

Use Thick Weed-Control Fabric/Weed Membrane

A weed-control fabric/weed membrane can prevent weeds from growing.

It’s perfect to use under paths or decking. It allows water, nutrients and air to pass through, while stopping weeds growing.

These are generally very easy to lay and offer a cost-effective way to prevent garden weeds.

If you want more information about weed membranes and how they can help, check out my weed membrane page.

Don’t Leave Bare Soil

Weeds thrive in open spaces in the soil. Plant vegetables, flowers and shrubs close together to minimise open areas where weeds can pop up.

Fertilise Regularly

Prevent new weeds from forming by using a fertiliser.

This can help build a healthy root system which can choke out weeds, whilst improving the condition and look of your lawn!

It’s important to note that the chemicals in most weed killers are not as effective during warmer temperatures.

This is not necessarily due to any shortcoming of the herbicide itself, but related to how plants absorb moisture. Most plants absorb more moisture in the cool temperatures of the early morning, but stop when temperatures rise in the afternoon.

So, for the best results, apply your weed killer early in the day.

All weed killers have the potential to be washed into other areas through rainwater runoff.

Spraying during windy conditions can also cause the chemicals to spread to areas that you did not intend to treat, killing plants that you wanted to save.

Therefore, you should avoid using weed killer if you know it’s going to rain or if it’s windy.

Weed Killer FAQs

Weed killers use chemicals (herbicides) to control, limit and stop plant growth. The actual chemicals in the formulation can vary depending on the brand and the type of weed killer in question. Many are safe for application on other plants (selective) although you should always read the packaging before applying them to edible plants that you intend to consume.

Some products are also rated as being safe for pets and other animals (non-toxic formulas), but others are not.

Non-toxic weed killers may contain active ingredients such as pelargonic acid and maleic acid hydrazide.

Pelargonic acid breaks down the cell walls of cells inside leaves. The cells then lose their structure and die. It will only work on the green parts of plants, and can therefore be used around trees, under hedges etc., without concern.

Maleic acid hydrazide is often used in crop management. It affects the plant’s root system and stops them from growing.

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