Quick Guide to Weedkillers and Killing Weeds

Theperfectgarden.co.uk may earn a small commission (at no extra cost to the user) from Amazon and other online retailers if a purchase is made after clicking a link. I appreciate your continuing support.

How do weed killers work?

Weedkillers work in a few different ways because plants grow in different ways.

Brushwood killers (for killing nettles and brambles) usually contain an artificial hormone which confuses the plant so it doesn’t know whether it’s growing up or down, so gives up and dies.

Glyphosate (for killing any weeds that keep coming back). Works by blocking pathways that the plant uses to grow.

Contact weedkillers (for weak weeds that just pop up randomly). Work by blocking how the plant feeds through light (Photosynthesis).

Good fast-acting weedkillers will contain a mixture of pelargonic acid, which destroys the cell walls of the leaf and a growth retardant hormone which prevents cell division at the root tips stopping the plant from regrowing.

Weedkillers come in three basic forms: Contact, systemic and selective.

Contact Weedkillers

Contact weedkillers will only kill the top part of the weed, i.e. the leafy part. The weed could regrow. Contact weed killers will make the leaves of weeds disappear but are not really effective. Vinegar will work just as well as a contact weedkiller and is cheaper.

Systemic Weedkillers

Systemic weedkillers will kill the whole plant including the roots. Systemic weed killers will kill everything and anything as long there is green leaf showing. The weeds will take a few weeks to die. The best weedkiller if you are patient and never want to see your weeds again.

Brushwood WeedKillers

Brushwood weedkillers will kill woody weeds like brambles, nettles and tree saplings. Brushwood weed killers will kill the whole plant. The weeds will take a few weeks to die. It is slow acting and may take a few applications but will do the job.

Brushwood killers
in stock
46 new from £6.99
as of 12th April 2024 6:04 pm

Selective WeedKillers

Selective weed killers will kill all weeds except grass. Ideal for killing weeds in lawns. The weeds will take a week or so to die. Actually, a very successful weed killer as long as you don’t want to kill grass!

selective killers

Super Fast WeedKillers

Superfast weedkillers usually contain a chemical that destroys the leaf structure and a growth retardant hormone that prevents the plant from regrowing. These weedkillers really are super fast. Weeds show signs of dying within a couple of hours. They rarely kill woody bark so you can use these weed killers under shrubs and hedges, with caution. The best of the lot, superfast, can be expensive but you will only have to use the chemical once.

fast killers
in stock
13 new from £17.95
as of 12th April 2024 6:04 pm

Want to know more about killing weeds?

Never buy powdered weedkillers they are messy and difficult to mix. Weedkillers supplied at the garden centre are notoriously weak, except for the Neudorff brands. Most chemicals from the garden centre that say they will kill the whole plant, roots and all, will eventually kill the plant. However, the usual ingredient, glyphosate is weak and the weed will require a few applications and a few weeks to die.

Buy professional-strength glyphosates such as Gallup or Rosate 360 which has more glyphosate per litre of concentrate. This ensures the weed receives plenty of chemical and cant outgrow it. This can be the case with ground elder and bindweed.

Please don’t use salt or bleach, these will poison the soil.

If you want to use a premixed weed killer, i.e. a weedkiller that you buy and spray, it will be slightly weaker than if you mix it yourself. If you have a small terrace or a path with weeds, the premix sprays are fine. Ensure that you cover all the leaves with spray and you may need to spray several times over a few days or weeks.

Hand sprayers for concentrates are relatively cheap and worth the investment.

I hope this has been a concise and helpful post on how to kill weeds. Unless you want to be organic, try not to pull weeds with long or large root systems out of the ground, you will break the roots and most likely allow the weed to propagate. Spray them with the systemic weed killer over a period of a few weeks.


You can find comprehensive information on how to kill weeds successfully HERE