Skip to main content

Weedkiller In Compost - A Warning From Charles Dowding

Published on June 1st 2019
A room with a table covered in houseplants, pots, tools and soil

Plant Care

Written by Charles Dowding
There is a growing issue causing grief to many gardeners worldwide, and I can only hope it's not affecting you! Certain composts, horse manures and hay are being contaminated with an invisible active weedkiller.

This content is hosted by YouTube

By showing this content you agree to the terms & conditions of

To see YouTube videos without this popup please update your cookie preferences.

I became aware of how widespread this issue is from the flood of comments on a video I posted about it, from gardeners who had previously blamed shortcomings on viruses, seed quality, aphids, or their own mistakes.
I have seen the damage at many gardens, and have suffered stunted growth on a few beds at Homeacres too. This was a result of using some horse manure I used last summer to bulk up a compost heap when green leaves were scarce because of drought.
Sweet peas
Aminopyralid-affected broad beans in front, unaffected behind (from earlier sowing too)
The worst affected vegetables are beans, peas, potatoes and tomatoes, with new leaves curling inwards, leaves yellowing between the veins and stunted growth. The pyralid weedkiller causing this problem will break down in time, but only when in contact with soil microbes: it persists for years in heaps of manure and compost.
The poison can enter horse manure if the horses eat hay that has been sprayed with the weedkiller.

The active chemical, aminopyralid, is present in:

- Banish

- Forefront

- Grazon

- Halcyon

- Pharaoh

- Pro-Banish

- Runway

Supposedly, it does not affect horses or people, but this is not proven. On plants, it causes new leaves to curl inwards, yellowing of leaves and stunted growth.
Plants without pots laid out on a table
Pyralid test 17 days after potting tomatoes into clean compost left, affected compost right
Sadly, this poison may be in green waste compost if gardeners have taken sprayed lawn clippings for recycling. Please don’t use weedkiller on your lawn because many contain these persistent pyralids. You or others will then suffer long-term damage to many plants, including dahlias, roses, apple trees and fruit bushes, as well as most vegetables. Least affected are brassicas and sweetcorn.
Several pots of basil on a bench
Basil plants potted same time into compost with aminopyralid left, purchased pottong compost right
I have also seen weedkiller damage on plants grown in many prominent brands of compost. This is a huge issue.

Related articles

In the garden


No-Dig, the Charles Dowding Way

Fresh from planting broad beans and clearing kale, No-Dig expert Charles Dowding sat down with Candide to tell us more about...
A group of people in a garden

Slow reads


Charles Dowding - No-Dig Advantages, Soil Tests and April Veg Tips

Most soil already has a good structure for plant roots to grow in and is full of growth-enabling organisms. Millions of fungal...

From the allotment


Charles Dowding - Starting Out With No-Dig and May Veg Tips

The answer is absolutely not! It’s better to preserve the existing soil life and structure and simply apply organic matter...