What is the Fastest Acting Weedkiller?

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The fastest acting weedkiller is acetic acid (vinegar). An organic weedkiller that starts to work within two hours after application. The second quickest acting weedkiller is pelargonic acid, also an organic weedkiller. These weedkillers work the fastest because they dry the plant out very quickly. However, they both work in slightly different ways.

In this Fast-acting Weedkillers article, we look at:

  • What are acetic and pelargonic acid weedkillers?
  • Why do they work so quickly?
  • Which weedkiller you should use.
  • The important difference between the two fastest acting weed killers.
  • Where you can buy fast-acting weedkillers.

In a Hurry? Here’s a Quick Summary:

  • Vinegar will NOT kill the plant’s roots.
  • Neudorff Weedfree WILL kill the roots of plants.
  • Vinegar and pelargonic acid are organic weedkillers.
  • Both are glyphosate free.
  • RHS Fast Acting Weedkiller contains acetic acid (Vinegar).
  • They are both safe for pets, children and the environment once dry.

What is Acetic and Pelargonic Acid?

These two acids are found in fruit and plants and acetic acid is even found in the human body, albeit at low levels. Acetic acid is the main component of vinegar and makes a very fast and effective weedkiller.

Pelargonic acid is derived from pelargoiums! and it’s ironic that it is used to control the growth of plants in organic situations. Pelargonic acid is one of the fastest-acting, “complete kill” weed killers on the domestic market.

Why do these Weedkillers work so Quickly?

I will try not to make this boringly technical! So, take a deep breath, both these weedkillers work by breaking down the plant’s cell walls, this then allows moisture and fluid to leak out of the plant, causing the leafy top growth of the weed to dry out very quickly.

TIP: Spraying weeds when the weather is very warm will help speed up the process dramatically.

The Important Difference Between the two Fastest Acting Weedkillers.

There is one major difference between the two weedkillers. Acetic acid simply breaks down the cell walls. Whereas, Pelargonic Acid changes the PH of the cells causing them to also break down and dry out quickly. However, this chain of cellular events allows pelargonic acid to be
combined with another systemic organic weedkiller that prevents the regrowth of weeds.

This is important because many weeds will regrow even after their leafy top growth has died off.

Which Fast Weedkiller Kills the Roots?

Pelargonic acid is the only fast-acting weed killer that can use a growth inhibitor. This will help to kill the plant completely, starving the roots of nutrients. Neudorff produces a weedkiller that has an organic growth inhibitor called Maleic hydrazide, this is often used in fruit and vegetable growing as a growth suppressant on suckers and shoots.

In acute toxicity studies, maleic hydrazide is “practically nontoxic” to birds, fish, invertebrates and honey bees. It is considered to pose minimal risks to birds, mammals, aquatic organisms, non-target insects and aquatic plants.


How Effective is Vinegar as a Weedkiller?

Strong vinegar (acetic acid) is effective as a quick contact weedkiller and will make the top growth of grass and perennial weeds disappear super fast BUT no sooner than you have turned your back, the weeds have regrown. Annual weeds with very small roots will not be able to cope and will not regrow.

Is Vinegar a Systemic Weedkiller?

Vinegar (acetic acid) is NOT a systemic weedkiller and it will not kill the roots of perennial weeds.

How Effective is Pelargonic Acid as a Weedkiller?

We think pelargonic acid is one of the best fast weedkillers on the market. In fact, it’s so good, that we’ve written a separate article on Neudorff Weedkiller, you can find it HERE.

Is Vinegar and Pelargonic Acid Safe to use in the Garden?

When released into the soil, these acids evaporate into the air where it is broken down naturally by sunlight. The areas can be planted after spraying.

Certainly, Neudorff Weedfree is safe for the environment, pets and children when dry. However “Garden Vinegar” can come in varying strengths of between 5% and 20% acetic acid, so it is wise to always read the instructions before use.

Does Garden Vinegar Smell?

Vinegar that kills weeds does have a slight vinegar smell but don’t worry it doesn’t smell as strong as malt vinegar. Use the juice of half a lemon or 10 drops of bottled lemon concentrate to reduce the vinegary smell.

Both weedkillers are glyphosate free.