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Gardening Which? compost trials


Greenhouse plantlets

Greenhouse plantlets

I was fascinated to read and see the results of Gardening Which? compost trials in this month’s magazine. The results are extraordinary and in many ways disappointing. The peat free compost just doesn’t cut the mustard – at best achieving 54% compared to the best buy 88% for seed sowing. Young plants did even worse 46% compared to 92%. Up until now I’ve tended not to buy the cheaper compost and was under the misapprehension that more expensive compost was better and would give my seedlings a better chance.

Last year I noted that Sarah Raven uses jiffy7s or multipurpose compost for seed sowing. Up until then I had always used seed sowing compost for raising seeds and switched to multipurpose compost – much cheaper and giving good results.

The Which? trials confirm this on the multipurpose compost front. Their best buy is B&Q Multipurpose compost for seed and young plants, they note,
“After six weeks without additional feed, this compost produced plants of exceptional quality and consistency.”
At £4.28 for 70 litres it was also the cheapest compost on trial. Score 88% on seed sowing 92% for young plants. The B&Q Sowing and Cutting compost had the same score for seed sowing (88%) but not so good for young plants (88%). Incidentally B&Q multipurpose compost won best buy in 2009 as well. Unfortunately the winners were not peat free.

The best peat free composts were New Horizon Organic and peat free growbag for seed sowing (54%) and New Horizon Multi-Purpose compost for growing on small plants (46%). The six “Don’t Buy” composts were all peat free with one just scoring a shocking 4% for growing on young plants!

Over the last ten years the proportion of peat used in growing media and soil improvers has dropped from 70% to 46% but the increased popularity of gardening has boosted the demand for compost so peat bogs are still at very much at risk.

The low scores of the peat free composts are depressing. Various companies are experimenting with natural additions to counteract the loss of peat and hopefully sometime soon these will be widely available.

Meanwhile I’m going to try the New Horizon composts and experiment from compost made entirely from grass cuttings and leaves which gave me surprisingly good results for seed sowing last year.

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  1. I still can’t bring myself to buy peat, even if that’s true.
    I know if you’re going to all the effort of sowing seeds and raising plants you want to give yourself the best chance of success but, with all the people now gardening as you pointed out Fiona, we’ll all raise wonderful young plants for a few more years and then…..what? No peat, no more peat compost, back to square one and an entire habitat wiped out.
    I think homemade compost is the way to go, or at least modifying bought peat-free compost. I’ve been making my own bonemeal over the winter out of poultry bones ChiotsRun (Chiot’s Run) . Do you think the saving will justify buying a rotary sieve like this I can make more potting compost?!

  2. devongarden

    I am not convinced that Which? gives enough importance to concerns about using peat. I also have doubts about their depth of understanding of environmental issues. I remember some years ago reading in Which? that there was no evidence to support organic growing as being healthier than using pesticides–and then reading, also in Which?, that you shouldn’t eat or use in cooking the leaves of celery because they had such high levels of pesticides in them! Joined up thinking? Not really…
    I will be using New Horizon again if I need new compost.

  3. Hi Fiona,
    Without seeing the parameters under which the compost trials were staged, it’s really hard to asses how valid the results are across the board. I wouldn’t be too quick to use peat, especially with all the concerns about peatlands not being a renewable resource. There’s a great blog here in the states written by 4 university garden professors called, not surprisingly “The Garden Professors”. They take on all sorts of gardening myths and put them to the test in real scientific monitored trials where you can see what they tested under what conditions and sometimes the results are really interesting. If you google garden professors peat moss and look for an article written 12-15-2010 by Linda Chalker Scott, she addresses concerns about the depletion of the Canadian peatlands and I understand that the same concerns are valid for the European ones.

  4. Margaret Thorson

    After trying all sorts of commercial potting mixes years ago we went to mixing our own of peat and sand with a bit of organic fertilizer added. We make up soil blocks of this mixture and start everything in it.

  5. kate (uk)

    I have used New Horizon for some years now, with good results.
    There was an interesting report last year – I fear I forget where,possibly which again- comparing growing re-using your last year’s multi purpose compost by adding new slow release fertiliser to it and new compost.The old stuff was as good as the new.I know what I shall be doing next year….bonemeal, here I come.

  6. I can never remember which sort I have used, but will try and keep better records in my new “garden journel”
    I was thinking about mixing up my own compost. I saved the compost from the grow bags that I grew tomatos in last year and have some homemade compost and leaf mold, thought I might mix in a bit of pelletd chicken manure and see how things grow – has anyone got any tips or tried this?

  7. Oooh! thanks for this post. I used peat free compost last year and the year before and have been VERY dissapointed – so much so that I am going back to multi purpose this year – I only use it for seed planting but the peat free compost produces such weak plants that it is really quite disheartening. This post was very interesting though so I might try some New Horizon this year but alongside the multi purpose.

  8. Tamar@StarvingofftheLand

    I wish someone would do this over on my side of the pond! So much of gardening is confusing because all the experts seem to have different opinions. A little empirical data is such a relief!

  9. Great post…….The B and Q Multipurpose is often on 3 for £10 i wait and stock up 🙂 I find it great for all round use, and i like that it isn’t too compacted like some of the cheaper composts which makes it difficult to get out of the bag.

    we are out of homemade compost for digging in , did the article review soil improvers at all? it’s been a while since i had to buy any but needs must!

  10. I stick to New Horizon multipurpose and find it the best of the peat-free composts. It suits me fine, but I don’t have the experience of growing in peat to compare it too!

    A Master Composter friend of mine has done a number of compost trials in his time, and he feels that the ones that contain a large amount of composted material (bark, or green waste) are rarely matured for long enough – which means their nitrogen content is used to continue the composting process, and not for growing your plants. We may have to get used to extra feeding!

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