Wednesday 22 July 2015

Consequences of herbicide contaminated grass and manure

Contaminated compost and manky manure
This year-old composted municipal waste might still be toxic to young tomatoes
Blogger Sue Garrett does excellent work publicising the dangers of the contamination of grass and manure with the weedkillers clopyralid and aminopyralid. The problem of weedkiller contamination is not a new one, but these two chemicals are particularly long lasting. They take more than a year to break down in the soil and are not degraded when they pass through a grazing animal’s intestine.
Tomatoes are particularly sensitive and the chemicals are an acute danger to seedlings and young plants.

There are several ways that these harmful chemicals might arrive in your garden. Verdone ‘Improved’ is an excellent lawn weedkiller to remove ‘difficult’ weeds from the lawn. It is unwise to use consequent clippings near ‘soft’ plants for as many as half a dozen mowings.

Aminopyralid is widely used in agriculture for broad weed control in grassland. If eaten by grazers it passes through the animal gut and appears in the droppings. Although there are meant to be controls, if you use farmyard manure  - even from seemingly innocent sources - you might contaminate your soil. The manure might be contaminated from its straw content or the actual droppings.

Farmyard manure is the very best way to add bulky organic matter and fertilise your soil. I have had trouble myself from contaminated  ‘free manure’ from the village stable gate and no longer use it. I must admit the weed seed it contains is for me the much greater problem. There are herbicide free sources of farmyard manure. Best to use them.
My own philosophy with my none digging and in-garden recycling ways is that I do not need to use farmyard manure. This is special pleading because for anyone with inferior soil adding manure is one of the very best and quickest ways to improve it.

It is quite easy to test your manure for toxic content by soaking a small amount in water before watering the ensuing liquid on sensitive test seedlings. I have not done this myself but would expect uncontaminated fresh manure to give a false positive!
(Sue Garrett has cast doubt on this in the comment column  and informs us that the herbicides do not show up. I leave the paragraph in because it is a way of testing for other contaminants)

Inferior seed and potting composts are sometimes made these days from composted organic municipal waste. Other suppliers use more appropriate organic sources and their products can be really excellent. The problem with waste from the green bin – ours is brown and we never use it – is that any lawn clippings containing rogue herbicides will lead to toxic compost, as will lots of other potential pollutants. Cheap potting compost if made from municipal waste will almost certainly damage your seedlings.

This leads me to suggest that you return to much superior peat composts. I am making today’s post a three part series about compost and will argue my case very soon.

I would like to make clear that there is no question of aminopyralid and clopyralid in manure or compost being toxic to ourselves or our pets.

Although the problem of lawn herbicide contamination is highly annoying I don’t want to over exaggerate the danger to plants. If contaminated lawn clippings are used as a mulch under husky trees and shrubs they are unlikely to cause any harm.  (But don’t use the first cut nor use them near soft vegetation).

I admit I have form myself and have used a herbicide containing clopyralid on my lawn. In my own case I never box off my mowings and my lawn is all the greener for the grass mulch.

A local issue.

I must declare an interest! There is a green waste recycling plant half a mile up the road. They are not our friends! Huge lorries and council collecting vehicles charge past our home. Cathi next door lives in what, three hundred years ago, was a gatehouse on a narrow country road. Her foundations vibrate and if you are standing near her front door you feel the draft as lorries rush by.

Recycling is big business. The taxes to councils are huge if they resort to using landfill for green waste. The cost of satisfying exacting composting standards is nearly as much. It is not surprising that many councils resort to the private sector. Nor is it unreasonable that entrepreneurial former farmers with their rural skills can satisfy a need. The standards of our neighbouring composter are high.

Most of the money made in this trade is that received for taking in the green waste. Green waste includes everything that the public chooses to put in their recycling bin. It potentially includes noxious perennial weed and club root infected brassicas. Tree pruners bring their prunings from all over East Yorkshire. A load of waste timber is grist to the mill.
Although we loosely call the product of this process ‘compost’ it is only a vague and not legally precise term. It in my opinion it does not compare with your own compost from your own heap and it is certainly not suitable used alone as a seed or a potting compost. 
The product of this process is of little commercial value. To the composter its disposal costs are more than its worth. Fortunately farmers are starting to overcome their doubts and are using it to improve their soil. Some sellers of our local sandy soil for landscaping purposes I believe use it to enrich their product

It might surprise you that I do not disapprove of the composting of woody prunings. When shredded and decayed they make excellent material.
It is amazing how all this rubbish is quickly transformed into a satisfactory soil additive. Commercial composting in many ways is a much better way to make compost and generates much higher cleansing temperatures than we can do at home.
There is an old phrase ‘rubbish in, rubbish out’. It’s not quite true with municipal compost. How much better however when it is  ‘good stuff in’. I would like to think this is true of all commercial seed and potting composts that are made from green waste. Roger, dream on.

I have supped with the devil
Father I have sinned and accepted two free large loads from our jovial recycling Yorkshire farmer. Last year he dumped it in the farm field at the edge of our garden. It is nearly gone now and has been very useful for ‘rough’ gardening tasks.
My only disaster was when I recently used the year old material to ‘improve’ my soil compost for sowing my tomato seed. It was a lapse in concentration and I must have been mad. The seed germinated and died and I had to start again.

I have used a thin layer of year-old local 'compost' to sow grass seed when restoring  lawn levels. The complete absence of weed seed - especially weeds that are coarse grass – make it of special value

You can read more about herbicide contaminated manure on Sue Garret’s blog.

This is the first post of three about choice of compost


  1. This is an issue of great concern to me as well. My tomatoes have suffered very badly!

    1. I know you buy good compost Mark - or perhaps for your tomatoes you use garden soil as I do. I presume in your case it came in through the manure?

  2. I am afraid that the water test will not work with this type of contamination. The active ingredients trapped in the plant material in the manure only breaks down when moved with soil organisms and isn't water soluble. The chemical is released over a period of time and not all at once. Some plants are less susceptible to damage than others. This material may be composted and then release the chemical when the compost is added to the soil and perpetuate the problem.

    Roses and raspberries are two,shrubs that react to the contamination ifmulched with affected material.

    Can I add that I have more info on this here rather than my blog.

    1. Thanks for the extra information Sue. I will amend the post.
      Sorry I spelt your name wrong in the link. As it has not brought a complaint from your goodself I won't bother changing it!
      I see you can't manage a live link in a post comment column either. For those who don't know if your reference is copied and pasted into google it will take you right there.

    2. I wonder Sue, if the test would have showed up from my pile that has stood outside for a year?

    3. Never noticed the mistake and I can do a live link just wasn't sure you allowed it click herel

      The problem is that manure can stand for years and still hang on to the contamination. The only way to release the herbicide residue is to mix with soul and let the soil organisms break down the lignin in which the residue is trapped. This is one reason that weeds can grow on an affected heap which can give the wrong signals.

      If yout heap sat on the soil then their may be some release at the very bottom of the heap where the soil is in contact

    4. By the way beans and potatoes are also particular;y sensitive and contamination can be carried forward bt volunteer potatoes coming up in subsequent years on an affected patch.

  3. Thanks for writing this. We should all be on our guard regarding composts that do more harm than good. I have also heard that manure from cows fed large amounts of antibiotics can be detrimental in the garden.

    1. I am not aware of adverse antibiotic effects in the garden Jason but excessive use of antibiotics by farmers is not a good thing as a result of the general problem that this leads to antibiotic resistance being shared around between bacteria.

  4. Sorry. Your putting an image that is permanently overlaid over text makes reading all but impossible. I will avoid this site from now on.


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