Putting Lawn Weed Killers to the Test

By Daniel at DIY Gardening

Written by Daniel Woodley. Reviewed by Elizabeth Smith. Published to Lawn Care on 28th August 2022. Updated: 22nd February 2023.

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If you want a lawn to be proud of, at some point you’ll need to take action against invasive weeds.

After years of growing a lawn and helping others, I’m confident I have a solution.

I apply two different weed killers, one in the spring and the other in the autumn.

This is sufficient to suppress weed growth, leaving space for the grass to thrive.

While there are hundreds of different species of weeds and invasive plants, I’ve found that just these two products are enough for treating lawns.

This is my review of Weedol and Greenforce lawn weed killers.

I Tested Weedol. This is What Happened:

In June 2022 I tested Weedol concentrate on three common garden weeds. I mixed the recommended amount of Weedol with water and sprayed the foliage lightly, minimising wastage.

Here are the results:

(Please ignore the brown grass, this is due to a drought and hosepipe ban here in the UK)

Test 1

Weedol test results (1)

Test 2

Weedol test results (2)

Test 3

Weedol test results (3)

As you can see from the results, Weedol didn’t kill the weeds instantly and in test 3, there was little difference from day 1 to day 7 – the weeds had even started to grow faster, albeit twisted.

By day 14 the weeds in test 1 and 2 were all dead and in an advanced state of decay. The weeds in test 3 took al little longer to die off.

Update August 28th 2022 – none of the weeds has grown back since I treated them in June.

FYI: Weedol contains Fluroxypyr, Clopyralid and MCPA.

The Weedol Product I Used

Weedol produces several different weed-killing products. This is the one I used:

Weedol - the strongest weed killer for lawns

I chose this product because it comes in concentrated form and once diluted, one 250ml bottle will produce 85 litres of weed killer.

I feel this is far more economical than buying ready-to-use bottles that only treat small areas.

Concentrated Weedol works out at about 18p per litre, once diluted, which is a bargain.

I also have experience with this product and have been using it for years.

Pros

  • It works, as tested by me in June 2022.
  • It’s by far the cheapest product I could find, 18p per litre once diluted.
  • It didn’t damage my grass.
  • Very little plastic wastage (like you get with ready-to-use products)

Cons

  • I had to dilute it so that means handling chemicals.
  • It doesn’t come with a measuring gauge, so I had to measure it myself.
  • It doesn’t come with a built-in sprayer, so I had to use my own sprayer.
  • As with all chemicals, I had to keep pets and children off the grass until it had dried.

Alternative to Weedol Concentrate

The concentrated version of Weedol is perfect for those with large lawns or those that are happy to dilute it with water but for those with small gardens, or anyone who dislikes handling chemicals, they also sell a ready-to-use version that is great for:

  • Small gardens.
  • Occasional use (ie spot treatments)
  • Those that don’t have space for a dedicated watering can or backpack sprayer.
  • Those unwilling to dilute/handle chemicals.

If Weedol’s Weed Killer Doesn’t Work

I’ve been using Weedol for years, and from what I can tell, it will kill around 99% of broad-leaved weeds that grow in UK lawns, but in my garden it didn’t kill every weed.

Greenforce is an alternative product that contains different chemicals:

Mecoprop P at 3.67%w/w

Dicamba at 4.657% w/w

If you have weeds on your lawn that don’t respond to Weedol, I’m 100% sure that Greenforce will deal with them.

This is why I use Weedol in spring and Greenforce in autumn – they contain different chemicals, and by using them both each year, I’ve been able to kill off all the weeds in my lawn.

I Tested Greenforce’s Lawn Weed Killer. Here are the Results:

In July 2022, I applied Greenforce concentrate to a patch of overgrown brambles, stinging nettles and other weeds in a corner of our yard.

I also sprayed it onto the grass, some nearby bamboo and close to some conifers.

Here are the results as of the 28th August 2022:

image not loaded

As you can clearly see, the nettles and weeds are dead and the bamboo and conifers in the background are unaffected.

I’ve used Greenforce in the past and based on my experience, it isn’t quite as effective as Weedol (it doesn’t treat as many weed species), but as it contains different chemicals, it will finish off any weeds that Weedol failed to treat.

Weedol is my number one choice, but for those with a real weed problem, I suggest treating the lawn with Weedol in the spring and Greenforce in the autumn.

What I Like About Greenforce:

Pros

  • It works, as tested by me in July 2022.
  • Like Weedol, the concentrated version is very economical.
  • It didn’t damage my grass.
  • Very little plastic wastage (like you get with ready-to-use products).
  • The Greenforce bottle comes with a built-in measurer which reduces spillages and ensures accurate dilution.

Cons

  • The chemicals aren’t as effective as those found in Weedol, based on my experience (I suggest trying Weedol first).
  • It doesn’t come with a built-in sprayer so you’ll need to buy one or use a dedicated watering can.
  • As with all chemicals, you’ll need to keep off the lawn until the product has dried.
Greenforce weed killer

To Remove and Prevent Lawn Moss:

None of the lawn weed killer products listed above are effective against moss.

Based on my experience, if you want to remove and prevent lawn moss, there are only two products I think you should choose from:

  1. Bacteria that eats moss (often called “No Rake” moss killers).
  2. Iron sulphate.

I have already written about these products, how to use them and what results I’ve experienced:

Read my guide to lawn moss removal and prevention.

My Experience with “All-In-One” Lawn Weed Killer Products

All-in-one lawn products contain a bit of everything:

  • Fertiliser.
  • Iron sulphate to control moss.
  • Weed-killing chemicals.

Based on my experience, “all-in-one” products are perfect for maintaining an existing lawn but they don’t contain enough of each chemical to treat lawns with severe problems.

Once you’ve used a dedicated product to get rid of a nasty weed infestation, you can use the cheaper “all-in-one” products to keep it under control and stop it coming back, but from my testing over the years, I feel that’s about all they are good for.

My Test of Manual Lawn Weed Puller Tools

In 2022, I tested two manual weed puller tools:

  • An upright weed puller by Fiskars.
  • A simple hand tool that yanks out the roots.

If you would like to try the chemical-free method of getting rid of lawn weeds, explore my review of the best puller tools.

Lawn Weed Killer FAQs

Can Lawn Weed Killers be Used on New Lawns?

I’ve found they can be used on lawns 3 months or older but I only use the weed killer during the spring and autumn, I avoid the height of summer when the lawn might be stressed.

How Many Times a Year Can a Weed Killer be Applied?

Most granular or concentrated liquid weed killers can be applied twice a year, I suggest one application at the start of the growing season in the spring. The second application can be in early autumn.

There’s no need to apply lawn weed killers in late autumn or winter as weed growth is limited at this time.

I avoid the height of summer as more people and pets are on it at this time and the grass is more stressed due to the heat.

How Long After Applying a Lawn Weed Killer Can Pets and Children be Allowed Onto the Lawn?

In most cases, pets and children can be allowed onto the lawn after 24 hours or after the product has dried, whichever is the longest.

Do Lawn Weed Killers Also Treat Moss?

No, most targeted lawn weed killers do not affect moss. I have used both Weedol and Greenforce on mossy lawns, and they had no effect on the moss.

Some, such as “all in one” products, may contain Iron Sulphate, which turns the grass bright green and also kills light lawn moss. However, I know from experience that these products are rarely effective against lawns suffering from severe moss infestations.

I recommend MO Bacter for lawn moss control as it contains safe bacteria that eat the moss but doesn’t harm the lawn, pets or the environment.

Can I Remove Lawn Moss Without Using Chemicals?

Yes, garden rakes and scarifiers can remove the moss and dethatch the lawn ready for overseeding with lawn seed. I’ve had great results using organic moss treatment products; these contain bacteria which eat away at the moss whilst leaving the grass unaffected.

Meet The Author: Daniel Woodley

Daniel has over 18 years of experience in the construction, home improvement, and landscape garden industries.

He previously worked as a project manager and has experience in managing teams of tradespeople and landscape gardeners on both small and medium sized projects.

Daniel is also a keen gardener and enjoys growing unusual plants and tending to his lawn.

More About Daniel Woodley.

Daniel Woodley

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This guide was reviewed and fact-checked by Elizabeth Smith.

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