The Strongest Weed Killer you Can Buy

The Nuclear Options + Alternatives

Tested by Daniel at DIY Gardening

I’m not a fan of using powerful weed killers, as I know from experience that if I keep on top of my garden maintenance, I rarely need to use any chemicals at all.

However, there are occasions when only the strongest weed killer will do the job:

  • Working with a very neglected garden.
  • Large spaces where it’s not practical to use tools.
  • Persistent weeds and invasive plants.

For tasks like these, there’s only one or two products that I would consider using.

My name is Daniel Woodley, I’m the co-owner of DIY Gardening, and this page is all about the strongest weed killers for specific scenarios.

Daniel Woodley

1) Doff Concentrated Strong Weed Killer

Doff strongest weed killer

Details

This is one of the strongest weed killers you can buy and comes concentrated, so you get more mileage per bottle.

This 1-litre product will, when diluted, treat up to 400 sq metres, so it is perfect for almost all domestic gardens.

Not only will Doff’s Weed Killer take out any known weeds, but it’s so powerful it will kill off most plants too; in fact, the only plants that could put up any resistance to this weed killer are ivy, the infamous Japanese Knotweed, bracken and tree roots.

This is not a weed killer for lawns or flowerbeds where you have lots of plants growing as it will take out everything. This is the strong stuff and is best suited to persistent weeds or situations where you need to destroy all plant life in a large area so you can start from scratch.

Specifics

  • 1-litre bottle.
  • Glycosulphate in liquid form at 90g per litre concentration.
  • Treats up to 400 sq metres.
  • Targets all plant life but works best on tender weeds.
  • No gloves or face masks are supplied.

Pros

Perfect for large areas of overgrown weeds and unwanted plants such as nettles.

Liquid-based and easily dilutable.

It can be used on hard surfaces (patch test first), although it should be sprayed onto the weed rather than liberally over patios/driveways.

It contains Glycosulphate at 90g per litre, which is suitable for all known weeds.

Kills roots as well as top growth

While very powerful, it breaks down into harmless by-products in the soil.

Cons

This weed killer can’t be used on lawns.

It will kill most plants on contact, so it isn’t suitable for flowerbeds with plants in them.

It can be slow to act as the plant must absorb the chemical where it then causes the cells within the plant to collapse; this can take 1-2 weeks before noticeable results; although the weeds will be dead much sooner, they may look green for some time.

This product can be very harmful to wildlife, pets, children and adults, and care should be taken to follow the instructions, especially with regards to wind, rain and skin protection.

There are stronger weed killer products (see next suggestion) for woody plants and even tree roots.

2) Roundup Stump and Root Killer (The Nuclear Option) 

Tree stump killer by Roundup

Details

While Doff’s very effective weed killer contains Glycosulphate at 90g per litre, Roundup Stump Killer contains the same chemical but at 441g per litre.

Needless to say, this is the nuclear option and is by far the strongest weed killer on the market.

Despite its name, this product from Roundup can also be used on plants including brambles, ivy, Japanese Knotweed and saplings as well as persistent weeds such as the notorious Horse Tail (which sprouts from underground tubers).

If you’re looking for a strong weed killer, choose Doff’s product but for the strongest, nuclear option, try Roundup Tree Stump Killer.

Specifics

  • 441g of Glycosulphate per litre.
  • Liquid form, dilutable.
  • 250ml bottle.
  • No mask or gloves supplied.

Pros

The strongest weed killer you can buy domestically.

Will kill all known plants.

One 250ml bottle contains enough dilutable chemical to create 25 litres of product.

Breaks down naturally in the soil.

Treats Japanese Knotweed and even Bamboo – plants that are notoriously difficult to get rid of.

Cons

Takes time until results are visible – usually up to two weeks.

Potential health implications if misused. Questions have been raised about the safety of strong weed killers such as this.

Not appropriate for widespread, non-targeted use as it’s too strong.

Smaller bottle and less coverage than Doff’s product.

Not suitable for lawns, flowerbeds containing plants or anywhere desirable plants are growing.

3) Strongest Weed Killer For Lawns

Weedol - the strongest weed killer for lawns

Details

Weedol’s Lawn Weed Killer comes in two versions, the watered-down “ready to use” product, which is a waste of money and plastic packaging and the concentrated strong version, which, when diluted, covers 330 sq metres of lawn.

As the name suggests, this weed killer is safe for lawns, even lawns sowed 2 months ago.

I’ve previously tested this and several other lawn weed killers and found that this was the best of the bunch.

Use Weedol on:

  • Daisies.
  • Buttercups.
  • Dandelions.
  • Plantain.
  • Clovers.
  • + many more.

Specifics

  • 10.7g of fluroxypyr per litre.
  • 5.4g of clopyralid per litre.
  • 53.4g of MCPA per litre.
  • Liquid-based and dilutable.
  • 500ml bottle.
  • 330 sq metres coverage.
  • Apply no more than twice per year.
  • No mask or gloves supplied.

Pros

Can be used on new lawns that are at least 2 months old.

Contains three active chemicals that each treat a different set of weeds.

100% lawn safe, provided the lawn is at least 2 months old.

Concentrated formula so you get more coverage and there’s less plastic waste.

Pet and child safe after 24 hours provided there’s no rain in that time.

Cons

Doesn’t kill every known weed or even every common lawn weed.

For complete lawn control, it should be used in conjunction with Resolva (Resolva in spring and Weedol in autumn). Resolva contains different chemicals that kill other species of weeds.

To protect the grass, this weed killer isn’t designed to be the strongest on the market, and it may take several applications, 6 months apart, to control the weeds.

For maximum coverage, lawn weed killers are best applied by sprayer rather than a watering can and this product doesn’t come with a sprayer included.

4) The Strongest Moss and Mould Killer

BAC50

Overview

Even the strongest weed killer will be useless against moss, mould, algae and lichens as these are entirely different species and require a dedicated treatment product.

The best chemical to kill these is Benzalkonium Chloride which is the key ingredient in many branded products, including:

  • Patio Magic.
  • BAC50 (a concentrated 50% product)
  • Smartseal.
  • Pro Kleen.

Benzalkonium Chloride is for use on hard surfaces only and shouldn’t be used on lawns or flowerbeds. Lichens (black spots on patios) can take weeks to lift off after treatment as even though they are dead, they still cling to the surface.

For lawn moss, try one of these strong products.

Summary

Glycosulphate is the strongest weed killer chemical on sale, but most gardeners won’t need a product this strong as more targeted chemicals are nearly as effective.

Health concerns about Glycosulphate have led several countries to ban its sale, but the general consensus is that occasional use by those wearing PPE is safe.

Lawn weeds should be treated with products that contain some or all of these:

  • Dicamba.
  • Mecoprop-p.
  • MCPA.
  • Clopyralid.
  • Fluroxypyr.

Moss, algae, lichens and mould on hard surfaces should be killed off with Benzalkonium Chloride while lawn moss can be treated with iron sulphate or a bacteria (bacillus spp) which eats away at the moss over several months.

I Analysed Hundreds of Weed Killer Reviews Online. Here’s What I found:

Before writing this guide, I read hundreds of reviews on Amazon and other sites, here’s what I discovered:

  • Most of the negative reviews were from people who didn’t wait long enough for the product to act.
  • Some weed killers cause the cells within the plant to grow quickly until they collapse and die; this can result in an initial burst of growth that some reviewers mistook for the product not working.
  • Weed killers are more effective during the growing season as the weed absorbs the chemical much quicker.
  • Lots of reviewers were misusing the product, for example, using a weed killer on moss.
  • Many reviewers were applying the weed killers by watering can which is wasteful, a small 5 litre pump sprayer would be better.

Alternatives I Recommend

Chemical-free weed killing methods have become popular in recent years as consumers are now more aware of the dangers chemicals pose to human and animal health.

Electric weed burners are popular, as are gas-powered burners.

Both are suitable for weeds on hard surfaces but they don’t kill the roots so repeat applications are required throughout the growing season.

This page lists the best weed burners.

Boiling water is also effective but wouldn’t be practical for large areas.

Pelargonic acid is a softer, more gentle weed killer that isn’t as effective but is far more environmentally friendly and is even included in many pet-friendly weed killer products.

Also, there are plenty of tools designed to pluck weeds and their roots from the soil and lawns, and some of these gadgets are very effective.

I Don’t Recommend

There is a lot of nonsense on the internet about “homemade” weed killers and how they are safer than commercial products.

While attempts to reduce the usage of chemicals should be applauded, most of these recipes contain salt, which is poisonous to plants and persists in the soil for years.

Our co-owner, Hannah, published a guide to homemade weed killers where she debunks many of the claims made by bloggers and spread by the echo chamber that is social media.

Vinegar does kill some weeds but rarely the roots, and it’s not practical for more extensive or even medium-sized gardens.

Author: Daniel Woodley

This guide to the strongest weed killers was created by Daniel Woodley here at DIY Gardening and was last updated in September 2021.

Discover more helpful hints and tips from Daniel over at the blog.

Daniel is a keen amateur gardener trying to reduce his reliance on harmful weed killers and other chemicals but accepts there is a  place for them in some scenarios.

He also enjoys growing vegetables and fruits, as well as his herbaceous border and container garden.

More About Daniel Woodley

Danny Woodley

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This guide to the strongest weed killers was published here at DIY Gardening

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