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Competing composts – peat-based vs peat-free

Best vs worst container composts

We’ve been testing container composts to find the best performers. As the industry moves to increase sustainability, can new peat-free composts compete with their traditional peat-based counterparts?

The results of our latest trial of container composts are in, and as ever they show a huge variation in quality. Out of 23 composts tested, only three are Best Buys.

Our ‘best’ and ‘worst’ photos spell out the differences between a good and bad compost – so if you want your plants to grow well this year, plump for a Best Buy.

The world of compost is changing. The government wants all growing media to be free of peat by 2020, which means the hunt is on for good, sustainable alternatives.

Peat-free goodness for your plants

Manufacturers are already on the case. Westland has come up with West+ wood fibre, which is made from Forest Stewardship Council trees. William Sinclair has developed Super Fyba, made from ‘oversize’, the woody material left over once green waste has been composted.

Which? has found that some peat-free products for containers are really good – one of this year’s Best Buys is a peat-free growing bag. But peat-free compost is not an easy sell.

While some people understand and care about the issues surrounding peat, many more don’t. Many consumers have low expectations of peat-free composts, and one compost manufacturer has likened selling peat-free compost to trying to sell alcohol-free wine.

Boosting your compost confidence

Because of this, the government is proposing a performance standard for composts so that consumers have confidence in future peat-free products. We’ll be interested to see how this develops.

Some composts (peat based and peat-free) are clearly not fit for purpose at the moment. The only way to test whether a compost is good is to grow plants in it, over a long period of time – which is exactly what we do during our Which? testing.

Do you care what’s in your compost, or do you just want it to work? Do you consciously choose peat-based or peat-free?

Comments

I like the photo in your introduction, Veronica. It must be very satisfying to have test results that show such a dramatic difference as this.

Now that peat-free products have improved, perhaps there should be a surcharge on products using peat and a corresponding discount on peat-free products. That would encourage gardeners to switch even if the don’t know or care about environmental issues.

Each year, like a lot of gardeners, I invest a lot of money in seeds and basket plants and fill a lot of containers with compost. I expect that compost to do one simple thing, namely provide a substrate for my plants to grow in (they don’t even have to feed them all summer as I add slow-release fertiliser). The photo on the left clearly demonstrates that some composts sold to gardeners can’t even do that and, as you say, is’nt fit for purpose. If I had been unfortunate enough to buy some of this compost I would have lost a year’s display and wasted my investment in plants. Would I be able claim against the manufacturer for this loss?

Just to be safe, I’m planning a round trip to my nearest B&Q!

J.Waring says:
1 March 2013

Despite the continuous worry over the amount of peat we use in our composts, high percentage peat composts are still readily available. Why? Because we all wish to have a ‘blooming success’ after all the effort we put in. I have every intention of using peat-free compost, but then often selfishly sacrifice my feelings for the environment because I am tempted in favour of what is usually a guaranteed growing medium – peat based compost.
Would it be feasible (or correct) for you to exclude composts from your tests if they contain a high proportion of peat – perhaps include those which specify say 30/40% maximuum – could this then encourage manufacturers to better and greater efforts in non-peat products? It must be off-putting for the peat-free providers seeing your league tables continually showing the peat-based in the top positions?

Is there a possibility that contamination by commercial herbicides is a factor in the poor performance of certain composts?

jack says:
3 February 2014

Yes, technically, but it’s unlikely to constitute a significant difference. About two-thirds of all peat-free composts currently available are only suitable for use as soil improvers or mulch – purposes for which only 2% of gardeners ever used peat compost. There is little screening of the materials collected for `green’ composting, so there is the additional problem that there is tremendous variation in the quality of material available within a particular brand. ie, one bag of peat-free will help your plants thrive, but another bag of the same brand will kill them quickly; toss a coin. My last experiment with peat-free compost cost me £30 in wasted seed back in 2012. When I emptied out the remains of the compost bag I found myself holding half a part-composted, part mummified rat, oozing yellow puss out of it’s severed guts. Mystery solved. There has been some improvement in peat free compost at the top end of the scale, but there is nothing yet to compare with peat as a seed compost.

The 2020 compost ban is illegal under EU trade laws and is going to fail as an administrative exercise – they’ve been working on finding a satisfactory peat free seed compost for fifty years and they have yet to deliver. It’s very unlikely that they’re going to turn up anything much in the next five years. Nor is there much scope for improving the ‘green’ compost process to the point where most of the supply succeeds, even as a container compost.

The light at the end of the tunnel isn’t the way forward, it’s a train headed this way fast. When the peat supply fails in 2020 the national newspapers will ask themselves why there’s suddenly one and a half million gardeners paying black market prices for peat ‘smuggled’ in from Scotland. At that point they are going to review the justifications for the insistence on peat-free composts. It’s going to be worse for the green movement than David Icke.

It is not going to do much to promote peat-free composts if the manufacturers are careless about quality control.

Mrs M L Salisbury says:
30 June 2021

I’ve had very variable results with Peat free compost, to the extent that I have concluded that the manufactures have enormous difficulty in mixing fertiliser evenly throughout the product. For example out of six sowings of sprouting broccoli only one succeeded, reaching 8 inches (20 cm) while the other five sowings languished at 1 inch (2.5cm). I tried Westland New Horizon as being recommend somewhere, Those were the results. Also one year I had satisfactory results with one compost but the next year the same stuff couldn’t grow our flower seeds. It is very worrying because I am on board with the reasons we should use peat free. I think we may try our council made free compost since we can’t make enough garden compost of our own.

Mrs Salisbury — I find that most compost gives inconsistent results for planting and I haven’t used any for growing from seed.

The compost you have used came out as a Best Buy peat-free material for cultivation from seed in Which?’s 2021 results but it contains no green waste. See –
https://www.which.co.uk/reviews/compost/article/best-compost-ahUv44C6lrR5
[the detailed results are only available to logged-in Which subscribers].

I am intrigued that you can get free compost from your local council. Is this the product of your garden waste collection service? Which local authority is it? I’d like to know why other councils do not provide free compost to the residents who supply the raw material at a considerable annual charge.

You could try a soil based compost – John Innes seed. I normally mix one of the JIs with a non-soil compost to get a better texture and water retention.
The danger of using home-made compost is the disease it may contain. I don’t know how clean council compost is as it might contain lawn weedkiller for example.