/ Food & Drink

Twisted tomatoes – is weedkiller in compost to blame?

Veg grown in compost bag

Have you had problems with plants grown in bought compost this year? We’ve heard stories that some tomatoes have shown twisted, distorted growth and had to abandon a trial of potatoes grown during our trials.

Recent media reports have suggested that clopyralid, a lawn weedkiller, may be present in composts. It’s thought that it may have got into mixture via council green waste, an ingredient in many bagged composts. Clopyralid contamination has already been a problem in the United States and New Zealand, so could the same thing be happening here?

The Sun’s Peter Seabrook has levelled criticisms at peat-free composts in particular as some contain green waste. But green waste is likely to be an ingredient in many composts, both peat-based and peat-free.

Herbicides affect garden growth

Now it wouldn’t be the first time that herbicides have affected gardeners – aminopyralid, a herbicide used on pasture, recently found its way into manure and then onto people’s veg plots, killing sensitive crops.

The Waste & Resources Action Programme (WRAP) is looking into the suggestion that clopyralid has got into composts, but points out that plant problems can be caused by a number of other factors, including viruses and over watering. It also points out that a compulsory test for herbicide contamination is carried out during the compost manufacturing process.

Digging the dirt

I wonder if gardeners know whether it’s safe to put grass clippings containing clopyralid on the compost heap or the council green waste. Labels on lawn weedkillers containing clopyralid (such as Evergreen Lawn Weedkiller, Verdone Extra and Vitax LawnClear2) are ambiguous, but in essence, any grass clippings that have come into contact with clopyralid should be put in the waste bin rather than used on the heap or put in the green waste bin.

I’m worried that manufacturers don’t spell this out for gardeners. Also, many people pay companies to care for their lawn, often using chemicals, and may have no idea that their grass clippings should not be put on the compost heap.

We’re keeping an eye on the situation and will let you know if we learn anything more. The compost that affected our trial is being analysed, and we’re also awaiting the results of our latest compost trials due to be released early next year.

In the meantime, if you’ve had problems with compost this year, we’d love to hear your experiences to help inform our findings.


I had not appreciated that clippings from treated grass should be treated differently, but this does not surprise me. If we assume that compliance is likely to be poor then why are these products licensed for use? Many gardening products have been withdrawn over the years and these weedkillers could be the next candidates to get rid of.

I try to minimise the amount of chemicals I use in gardening. How I tackle weeds on the lawn is to put a small amount of weedkiller in the centre of dandelion etc. rather than treating the whole area, most of which has no weeks. Doing this four or five times a year keeps the grass weed-free and a box of weedkiller lasts years.

Donald F Lee says:
24 October 2012

About this time last autumn I planted sweet pea seeds as usual and got a very poor germination rate. As it was old seed I thought that this was the problem so bought new seed. This new seed and seed collected from the remains of last year’s crop were planted in the same commercial compost and again produce a poor germination. I kept the pots with some plants in them but the plants just did not grow. Come February I planted seeds of all three seed batches in material sieved from my compost heap – excellent germination! When I tipped the earlier plants out the roots were at most only a couple of cm long, very branched and kinked. Unfortunately I had not kept a record of the brand of the comercial compost.

Kate V says:
26 October 2012

Like a lot of gardeners my plants struggled with this summer’s poor weather and low sunshine levels. I have two large window boxes which I re-plant each Spring and then again the following Autumn. I used Westland Container & Hanging Basket compost and planted antirrhinum(bought as young plants), mesembryanthemum (grown from seed) and one hebe ‘Heartbreaker’ in each box around about May time. I also added – despite there already being nutrition in the compost – slow release pellets in plug form which I have done for many years past, with no detriment to the plants. The boxes face south but my plants really struggled, despite being in the best position possible to benefit from any good weather.
For the Autumn planting, done towards end of August, I changed to Miracle-Gro Pots & Containers with moisture retaining granules compost. I can’t believe the difference in growth of the plants. The hebe was left in the box with its roots undisturbed, but surrounded by the new compost. The plants are twice as big as they were at the end of the Summer with violas, helichrysum seritonum, silene Druits variegated and sedum Rose Carpet surrounding the hebes and all are doing extremely well despite the weather not having improved. I can ONLY put this down to the compost. I also grew some viola seeds bought at Chelsea using the first compost. I got good germination, but after that it was a struggle to get the plants going. A few grew about 6 leaves and then just sat there not growing. I then tried them in the new compost and they have improved no-end. The antirrhinum were split up and planted in the garden where they are now re-flowering, something that didn’t happen in the boxes. I will not be buying Westlands compost next year!

Alan Preece says:
29 October 2012

I bought 3 bags (3 for £10) of Miracle Gro general purpose compost and planted out tomatoes, courgettes, cucumbers and peppers which were healthy seedlings grown from new seed. There was just no growth at all in compost from two of the bags, so I potted up some in a much more expensive (Forest Gold) compost using the left over seedlings. These rapidly overtook the first plantings and gave some yield albeit a bit late and into lousy weather – even the ones I put outside did better than the first plantings in the greenhouse, and the only cucumber plants to produce anything were the two I put outside, and one I rescued and replanted in the new compost. I dumped the rest of the Miracle Gro compost and next year will fork out for the more expensive compost – it has a much nicer texture anyhow, whereas the Miracle Gro (which I used happily in the past) was like coarse fibrous chippings.

Gary Hughes says:
30 October 2012

Having read the article in this month’s Gardening Which the symptoms described, particularly in respect of distorted tomato plants, exactly match my experience.

I planted a number of varieties, including Orkado, recommended as a result of last year’s growing trials. I used two different composts and, particularly in the case of Orkado and Marmande, I was therefore able to directly compare the results of growing in each compost.

The differences were so striking that the plants looked like different species rather than different varieties. One group of plants grew well, or as well as could be expected in what we laughingly referred to as our summer, whilst the others grew very slowly cropped poorly and the foliage was very badly distorted.

The resulting plants and fruit were so unappealing that I suspected weedkiller damage and, whilst I grew on the plants for comparison purposes, we did not eat the fruit.

The two composts I used were:
J Arthur Bowers Multipurpose.
Westland Multipurpose with added John Innes.

Unfortunately I didn’t make a note of which was which so I cannot identify the compost that gave rise to the problems but maybe, if they get enough feedback, Which can do this by a process of elimination.

Dave Allan says:
3 December 2012

I have a gardening column in The Herald’s Saturday magazine and my firm, ASK Organic, has been in partnership with Scottish Borders Council since 2005, giving home composting advice to householders in the local authority area.

I have looked into the clopyralid issue and published my views in my column and on our website. Essentially, the synthetic chemical, clopyralid takes at least 18 months to break down in any composting process. Householders using the chemical, and most others, are told not to compost the first 2 or 3 batches of grass clippings. How safe are later clippings? Some companies that provide lawn care services refuse to give details about the chemicals they use.

Apart from the damage to plants and wildlife, the chemical may be brought indoors on children’s hands and feet or on pets’ paws.

The chemical is banned in some parts of the world. It surprises me that the U.K. government hasn’t adopted a similar policy. The solution meantime is for householders not to use lawn fertilisers and herbicides. If they insist on doing so, they should not compost any grass clippings and should consign the clippings to landfill, never to a green waste collection. Gardeners should be responsible about this as Local Authorities should not have to, and probably cannot, protect their green waste from this kind of contamination.

David says:
6 January 2013

I too have suffered with poor material and traces of herbicides in growbags. In 2012 I had one growbag which produced stunted growth. Other growbags with the same batch of plants were quite normal. I wrote to the manufacturers J Arthur Bowers and complained of foreign material in their growbags. Their response was exactly the same as when writing about previous problems with foreign objects found in their bags. Their explanation is that these foreign objects come from their suppliers of compost materials and that they are making changes to the selection process and screening methods. They also suggest that I use Traditional Potting Compost in future rather than growbags since this is made up of 100% professional grade peat and has nothing else added other than some nutrients.

J.Mosse says:
8 June 2013

I have just found the same with New Horizon Organic compost ,in which my lettuces and beans failed.The beans that did come up were distorted.Cabbages were fine. That would be typical of clopyralid from lawnmowings or aminopyralid from farm manure. Organic????
Dow chemicals who produce these poisons say the labels are explicit as to preventing this from entering the recycling chain. Yet we have found that our horses manure has caused severe herbicide damage to cucumbers I grow in hotbeds , and this has to have come from haylage or straw which in theory should never have been offered for sale if treated.
To be stuck with valuable manure that we cannot use and be unable to sell our crops till this is sorted is heartbreaking.
Traceability is impossible as fodder merchants have little idea of which batch comes from where.
I could spread this onto my fields, but I would lose the wildflowers.My fields would start to look like the green deserts I see too much of round here .no buttercups, no butterflies., no birds. These herbicides kill clover too, so increasing the need for nitrates. This is crazy.Why on earth cant people appreciate the beauty of speedwell and clover in a flowery lawn?
Looking at gardeners forums it is clear that this is a huge problem . It is time to ban these herbicides altogether.