Horse Manure


This topic contains 36 replies, has 13 voices, and was last updated by  Steve Long 4 years, 11 months ago.

Viewing 15 posts - 1 through 15 (of 37 total)
  • Author
  • #46874


    Hi Charles,
    Unfortunately I have had further bad experience with horse manure.
    You will no doubt recall my hideous experience with buying and spreading on my garden, 16 tons of well rotted Horse Manure only to discover that it was all contaminated with Aminopyralid herbicide and having to remove it all. Not the best gardening experience I have ever had!

    I successfully completed this and used Green Compost last year for my 6 inch mulch supplementing with Chicken Manure pellets and produced superb results.

    Having suffered the bad experience with Horse Manure I vowed never to use it again unless I know where it comes from. I have a field adjacent to my garden where horses are grazed and I know that NO herbicides are used and so last year I collected a heap from the field and left it in a pile for 12 months.

    I thought that I maybe missing out by not using manure and I do know that no herbicide is used on the field, so I was totally confident about the manure I collected and I spread a couple of inches on my veg beds this Spring to give the soil a “boost”.

    First crop I planted was 50 Broad Bean plants sown in the greenhouse. I planted these in the same position as last year which produced superb plants and a great crop in the green compost. After a few weeks it became apparent that the plants were not doing great, and on close inspection to my absolute horror I concluded that they were showing clear signs of Aminopyralid herbicide contamination.

    I immediately started a bioassay (24 April) using the suspect manure with broad beans, and a control using garden compost. I can now report conclusively that the manure contains AP herbicide. The curled growth in the suspect manure is clearly evident, whereas the garden compost is producing open growth as you would expect.

    The horses in the field where I collected the manure from, are fed with bought in hay to supplement the grass which all but disappears during winter so the only possible conclusion is that the Hay has been sprayed with herbicide. Fortunately nothing much else has been affected so far and I only have to spend a couple of hours scraping off the contaminated manure before I plant further crops.

    I have attached images of the Broad Bean in the veg bed, and the 2 pots used for the bioassay, one with suspect manure and the other with garden compost.

    I would just like to add a note of thanks to Dow Chemicals for the ruination of yet another crop!



    Images attached.

    You must be logged in to view attached files.


    Images attached

    You must be logged in to view attached files.


    Hi Mark and this is so maddening.
    I attach two photos of growth in normal and aminopyralid-affected compost, to help any others with identifying the issue.
    Symptoms include curling of new leaves, pale colour and small size.

    You must be logged in to view attached files.


    Does this problem only involve horse manure? Cows manure is never mentioned: maybe their digestion is more thorough?



    Yes it is Charles. I had complete misplaced confidence in the manure from the field next to my garden. I have tried horse manure from several different sources now and all of it has been contaminated with herbicide. I will never use it again, but all is not lost as I had great results with the green compost and chicken manure pellets last year so I will continue mulching with that and I will also have a fair quantity of garden compost ongoing.
    I felt my experience was worth posting to warn others using horse manure to always test it before use. I find it extraordinary that all gardening programmes and many magazine articles recommend using horse manure but I have never seen a warning of the risks. I suspect that many gardeners suffer the consequences of herbicide in horse manure and never identify the cause of their problem.



    Sorry to learn of your experience, its worrying at a number of levels. I believe that its actually advised that crop residue treated with this compound, should not leave the field.
    Dow are aware of the issue, see their information site at :
    Unfortunately there are no ‘approved standards’ for the manure supplied; although your suppliers’ forage should have.
    Having seen the “greenwaste” bin at the local amenity site, and the dubious material it contains, I am fearful of this material also, especially in the light of lawn weedkiller .



    Yes Cleansweep it seems farmers sign an agreement that ‘produce grown with it does not leave the farm’.
    So much for signed papers!

    Dalesman, cow manure is safe from aminopyralid because it’s an expensive weedkiller that they don’t need, mainly because they make silage not hay, and silage is cut before ragwort might be much grown + their leys are recent rather than old pasture, also because they are on a tighter budget than horse owners.
    I do wonder about the fear of ragwort and whether this helps Dow to sell their horrible herbicide.
    It is also in some grass mowings, not much yet as far as I can tell.



    Out of curiosity, I hope as I got some horse manure very recently, does this noxious stuff eventually break down if left for long enough? Will anything grow in it or are all non-grass plants damaged?



    Erica, yes it will break down if mixed with the soil but it can take several years. Most affected are Broad Beans, Runner and Green Beans, Tomatoes, Potatoes, carrots, Onions.



    Hi Charles and Mark,

    I fear that I too have become a victim of Aminopyralid contamination. I thought I would post here as a follow up to yours, and thank you Mark for all your posts on the subject, hugely helpful, and of course Charles for your continuing wonderful and generous advice on all things.
    In brief, I took on a plot last year at my local allotment. Hadn’t been touched for 5 years and I’ve had a great time returning it to cultivation, based on Charles books, videos, forums, and courses! Initially I covered with bagged compost about 5cm deep and covered in fabric (Permatex) from June 2017. I removed the fabric end of March 2018 and made 20 beds of 4.8m x 1.2m. I used well rotted horse manure from a local farm. I did ask them about Aminopyralid (oh no nothing like that), and since our allotments have always used them I figured it would be fine. And then covered the horse manure with a few cm of the finer bagged compost.
    All seemed fine, initial growth was excellent, weeds have been scarce. I also constructed a greenhouse in the spring and filled the bed with the same horse manure and compost.
    20 June was the day I realised this might be Aminopyralid.
    Potatoes (King Edward) were starting to show leaf curl after a healthy start. Dwarf French Beans Speedy were doing badly, I had initially assumed due to cold nights. Broad Beans, previously growing well, started to show distortions. Tomatoes in the greenhouse were showing some leaf curl.
    I started a bioassay test on June 25th. Six 5″ pots with a 50:50 mixture of the well rotted horse manure and multipurpose compost, six pots with just the compost. Four different bean types in each (Greek Gigantes, Dwarf French Bean Speedy, Climbing French Bean Cobra, Broad Bean Aquadulce Claudia). Those in the compost only pots grew fairly well, those in the mixture were poor. I’d had 3 x 4 tonne deliveries of the horse manure over the months, and I used two samples from each batch. Pics below.

    Despite this, some plants have done well. Tomatoes (Sungold, Sakura, Iris), mostly in the greenhouse, have been super productive, but had quite a bit of leaf curl. I assumed this was AP, but maybe its leaf roll (he said hopefully)?
    Potatoes were doing really well, but started to get leaf curl in June. Charlotte still produced well, King Edwards not so well. Peas were very successful, but French Beans (Speedy and Cobra) planted in the same bed were terrible. Greek Gigantes Beans started badly after planting out, but after a month have come back to life and are now thriving. Jerusalem Artichokes (which should be v. susceptible?) have had mixed results, most showing leaf curl at some point, most recovering fine, a few less so. Onions have seemed Ok but not very big, beetroot good, corn good.

    So I’d appreciate your view on all this. I have assumed this is AP and that I’ll need to strip all the raised beds off and start again. Which depressed me for a few days back in June, but I’m over that now!

    Many thanks if you got this far!

    You must be logged in to view attached files.


    And a few more pics to add to the above post

    You must be logged in to view attached files.


    Ah Paul this is so frustrating after all the effort you put in to reclaim the wild area.
    I would not remove what is there because I suspect the ap has finally or almost finally broken down, in contact with soil organisms.
    Your crops are certainly not the worst and greenhouse tomatoes show a mild effect only.
    Do a bioassay on a bed with a few broad bean or pea seeds.

    Sarah Raven suffered it this year with here fine new bed of dahlia bulbs. She was so upset and has got her MP on it and the NFU, I hope that makes a difference as this stuff is lethal and should not be allowed ever again.
    Farmers are supposed not to sell treated material, and they sign an agreement to that effect: your farmer must have done that, unless nobody is enforcing it.
    It’s a legal requirement, was a condition for Dow being allowed to sell it again after the original ban.



    Paul, so sorry to learn that you have encountered this problem. I know it is soul destroying. The problem is that yes the farmers no doubt have all the right paperwork but they continue to use AP because they don’t think anyone will ever know. Indeed I doubt that I would have ever known what I was up against if it hadn’t been for you Charles. Even if you ask the horse owners they dont have a clue what goes on with the hay they buy in, which is what happened to me on the third disaster. As Charles says the AP appears to be fairly mild but from what I have read the effects can last for years and the recommendation is to rotovate to mix with soil organisms to break it down. The problem with that is that once the manure has been rotovated there is no way to remove it if the effects do remain apparent. I think if I was in your position Paul I would remove the manure from at least some of your beds for next year. On a positive note the shovelling is great excercise! I will never use horse manure again but I have had good results with green compost so I cant see any point in risking the work and disappointment for manure. So if you can find a supply from your local authority that may be the way to go. You should report this to Dow chemicals.



    Helpful tips Mark.
    On longevity in soil, I reckon it depends on the amount/concentration in manure.
    Paul seems to have relatively little and I suspect it is mostly gone now.
    The advice to rotovate (aargh) is just taken from the lexicon of misunderstandings about soil, and what do Dow know or care?
    Rotovating kills a lot of microbes.
    Whereas compost (old manure in this case) encourages microbes, worms etc to feed at the surface, as is their habit. Breakdown of ap should then be quicker than if it were incorporated.

Viewing 15 posts - 1 through 15 (of 37 total)

You must be logged in to reply to this topic.

Forum Info

Registered Users
Topic Tags