The Ins and Outs of Choosing Bought Compost

Compost is the heart and soul of your garden. Does it matter which compost you buy? Damn straight it does! Well made compost is all our soil needs to grow abundant crops with minimal disease. But rubbish in, rubbish out – compost made with sub-standard ingredients will wreck your soil and your crops. Here are the three key things to look out for when buying compost.

Undercover and in the Shade

Compost is a living product – not that well suited to life in a plastic bag. Once it gets sealed it starts going downhill from there and if it’s sitting out in the weather, especially the sun – it’s speed skiing its way to oblivion. How I’d love compost to be dated. Integrity! Be sure to choose bags stored under cover and in the shade.


sniff the soil

We’ve all walked past piles of compost bags and recoiled from the smell. Sour smelling anaerobic compost is nasty. There will be no soil life at your place if you put this muck on. Musty smelling compost that’s died and gone to heaven isn’t as dangerous as anaerobic stuff, but a complete waste of money. Trust your nose, my friends and walk on by.

Pyralid Weedkillers in Compost

Clopyralid induced damage in a tomato plant Bezdicek
Clopyralid damage. Photo by David Bezdicek source

I first became aware of herbicide in bought compost in the early 2000’s when a school garden failed to get going. Potatoes sprouted but were curled and distorted. Tomatoes and beans did the same. We presumed spray drift to be the cause until another school garden with the same compost had exactly the same experience but no possibility of spray drift. I started asking questions.

Sounds scary. And it is. Pyralids are a group of persistent herbicides that, if present in your compost, will wreck your crops. It totally deserves its nickname “killer compost”. Bums me out that this spraying is still going on in NZ, but keeping it real, our people are choosing it – so best you are aware.

Clopyralid, Aminopyralid and Picloram are the foes here. They’re used on sports turf, golf courses, school grounds, road sides, hay paddocks, forestry and on home lawns (even though its illegal for home use) to kill broadleaf weeds, thistles, dandelions and clover. Whaaaat dandelions + clover! If only there was an emoji for rocks for brains.

The magic of pyralid and the reason it gets used so lavishly, is that grass and all its relations like corn, continue to grow on nice and happily thank you very much. They are of course saturated in it which is how this stuff lives on in grass clippings + greenwaste, in the manure of animals that graze on grass sprayed with it and in hay from paddocks sprayed with it. It’s so persistent it lives on after the composting process – intensifying in strength even. Yip it lives on and on. 

What’s a Home Gardener to Do? 


Home made compost is your safest bet. But who can keep up with demand?! Not me. If you do buy compost in quiz your suppliers. Get asking my friends. Nothing makes change like consumers – you and me and all our friends and aunties (especially the aunties) – getting on the job. 

Find out whether or not they use grass clippings, greenwaste or manure or carcasses from non organic farms – if they do you can pretty much guarantee pyralids.

Let’s keep composters on their toes and let them know that we know. We’re not paying for herbicide residue and soil wrecking compost! We’re growing food … we want good, wholesome compost.

Test the Soil With Seeds

Before you spread bought compost, take two weeks out and do a grow test. Once its on your gardens, theres no going back and heartbreak will ensue as you watch your plants curl up their toes.

Sowing broadbeans or tomatoes into it will show you whether or not pyralids are in the house. A control group of seedlings is sensible so you can compare growth rate and distortions. This is especially useful when pyralid concentration is low and the differences are subtle.

Grow seedlings on for a few weeks. If the compost is poisoned seedlings may not germinate or will grow slowly, be stunted and growing tips will be curled, cupped, twisted – generally distorted, and looking exactly as if herbicide has drifted over them.

How to do your own grow test and pics of affected plants.

Dont Blame the Composters

Lets be fair. Composters are recycling all the waste from our lives. The only way to stop this nonsense is to stop giving your dollars to non organic growers and farmers and to get involved in your commmunities and shout out about pyralids on school fields and parks. The less people that buy sprayed meat, vegetables and fruits – the more farmers and growers will turn to holistic methods.

All their waste has gotta go somewhere. Its in our loop, cycling back as not only compost but into our waterways, air and the very core of our wellbeing. You gotta wonder.


  1. My raspberries were very crumbly this year, and the leaves were full of holes. My bushes are several years old. My husband does prune them, but either in the spring or fall, because we are not here in the winter. Any suggestions to have better berries
    Thank you

    • Could be a few things Marti – either viral if the leaves yellow then crumble, or dry berry if there are reddish blotches on the leaves or even mites if the leaves are mottled. Either way spread good compost at the base of the raspberries. Prune any damaged canes. If you have chooks get them under them to clean up larvae. Foliar spray with Neem and EM and seaweed once a week as a good general baseline for all of the above apart from viral disease. Build beneficial insect population with perennial companions nearby. Pay close attention to the progression of the leaves and canes through the season – photos are a great idea to get a clear diagnosis.

  2. Hi Kath
    What do you do if you’ve got bagged compost and its in the garden…do the pyralids continue on ad infinitum? I now know why my tomatoes were all curled last year.

    • Good to know – even if it is sad news. The best treatment is sunlight and soil life, who are I feel super forgiving of all our insensitive, uncaring human ways (the compost maker not you that is) Uncover the soil if its mulched, drenched it in EM and leave it to nature. You can test it by doing a grow test as per the bottom of the article. If there are still signs of curling in your test seedlings then grow a mustard greencrop. Keep testing until the all clear.

  3. Avon Lookmire says

    Asked my local supply yard today what’s in their compost and they told me they get it from paranui organics 😊 Sometimes the world just makes things easy and simple 😊

  4. Thanks for the lists of suitable bagged compost. Whilst we have started to make our own compost for general use in the garden, have used bought bags for when planting new fruit trees.

    I use a liquid seaweed mix as a nutrient boost when watering new plantings – but in one of your above replies, are you saying to use seaweed as part of a spray to prevent non-viral disease?

    • Seaweed is an awesome all round strengthener for your whole system. It feeds beneficial bacteria, strengthens plant cells and adds the full spectrum of minerals which is what our plants need for best health. My goal is to get the whole system jamming, in the same way if you eat a whole food diet and rest and be happy you stay well. Hope this helps! Kath