Why Potting Soil Made From Recycled Waste is a Great Idea

, written by Jeremy Dore gb flag

The huge industrial shredder used at The Compost Shop to crush recycled green waste

Soil quality is the most important factor in any garden and even more so when you are planning to eat the resulting produce.  To enrich my soil I have been composting my own garden and food waste for years but, like many gardeners, I find that it is hard to produce enough to cover the whole area.  This year I have been transforming my front garden into a network of raised beds to be built up with high-quality compost.  I wasn’t content to go for the cheapest stuff I could find, so a bit of research was in order.  This culminated in a visit to a composting site, to find out just what goes into compost and how organic it really is...

Compost is the best treatment for almost any garden.  Of course, gardeners often use manure, seaweed extracts or manufactured products to enrich soil but they can have their disadvantages (see my article on The Problem with Manure from last year).  In contrast, compost is:

  • Cheap and easy to get hold of
  • Good for enriching all soil types: it helps break up heavy soils and improves the nutrient and water retention of sandy soils
  • A great way to recycle waste and reduce the amount that gets unnecessarily sent to landfill

Traditionally commercial composts have used non-renewable resources such as peat but increasingly other options are available and most of those contain recycled plant waste.

To find out more I visited The Compost Shop in the North of England, a large recycled compost producer.  They recycle about 15,000 tonnes of green waste from local council collections every year and turn it into high-quality compost and topsoil products.  Their manager, Ben Jackson, gave me a tour of the site and explained the process:

  • Green waste arrives at the site and is initially sorted to remove undesirable content.  This is a laborious process as some people still throw plastic bags or plant pots in with the waste, which must be removed by hand.
  • A huge industrial shredder is used to chop and crush the material (pictured above) before being fed into a screener which removes material larger than 30mm diameter.
  • The waste is then mixed in huge piles, producing the ideal mixture of moisture, air and green/brown material.  These quickly heat up through the microbial activity which is the basis of hot composting.  Temperatures reach up to 170°F (75 °C) which kills all weed seeds and ‘burns off’ any undesirable elements such as weedkillers.
  • This mixture is turned 8 times during the 12 weeks it takes to complete the composting process.  Temperatures are monitored daily for the first half of this period, ensuring that the mix remains above 140°F (60°C) for at least 5 weeks.  In fact, you can see clouds of steam rising from the piles as they are turned – particularly striking on cold winter days.
  • Finally the matured compost is screened down to 10mm size and samples are sent for testing.  The result is a high-quality sterile compost that won’t contain active weed seeds and is packed full of the nutrients plants need to grow.

Ben was quick to point out that this isn’t the same as the potting soil you would use to raise plants in pots.  Compost from this recycled process will always contain a sizable proportion of material which has yet to break down.  In essence, it is not as ‘even’ and free draining as the products used for germinating seeds.  However, this is a distinct advantage when adding it to garden soil or using it as a mulch.  The mixture of material gives it a very fibrous content which conditions soil well and the proportion of partially broken-down material means that it will release nutrients over a long time as these continue to break down.  Potting soil, with its intensive nutrient balance and very even texture, is just what delicate seedlings need.  However, it isn’t long before the nutrients are depleted and, as most gardeners know, after a few weeks you have to add fresh compost to the pots or supplement with liquid feeds.  Recycled compost, on the other hand, is a slow-release source of nutrients that will improve soil structure and feed plants for many years.

Making compost from recycled waste

So, what should you look for when purchasing commercially produced compost?  The following factors are important:

  • The source of the material.
  • The composting process being used
  • The tests and monitoring that are done
  • What happens if compost fails the tests

The Compost Shop take samples from every batch which are sent away for extensive analysis before they can be sold.  They were happy to provide me with a complete list of the analysis done on each batch which includes tests for toxic materials such as heavy metals, pH, pathogens and even the growth of tomato seedlings, checking for abnormalities.  They have occasionally had batches which have failed the stringent tests and which are then subjected to further composting and verification. 

In the UK the process to look out for is British Standards Institution’s PAS100, on which the Soil Association organic standard is based (even though many companies don’t then pay the extra fee to have the certification logo).  In the US look for the US Composting Council’s Seal of Testing Assurance (STA).  These standards usually ensure that everything from the materials used to the laboratory testing are carefully monitored.  In many other countries there are statutory regulations but you may need to check exactly what is covered if you are keen to stick to organic principles.

I have been making compost at home for many years.  I like knowing exactly what has gone into it and how it was produced.  But I have to admit that the quality of the commercial recycled compost is considerably higher – a much darker, richer texture and no chance of weeds surviving.  So, this year I have ordered 3 tonnes of compost from The Compost Shop and will be using it to boost my garden soil into a rich paradise for vegetables!  I wish I could produce enough compost to do this myself but in the real world I know that composting on a commercial scale yields a superior grade of soil conditioner that will allow me to reap benefits for years to come.  What is more, I now feel much more confident, knowing just how it has been made and tested. If only shovelling all that compost were as easy as ordering it...!

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Comments

 
"I have seen the compost site for the compost you can buy at Norfolk recycling sites. It is excellent. The process is good, and the quality is good. The guy who set up the site is totally committed to both waste reduction and the compost they produce. I have loads of their compost on my garden. The only problem is it comes in bags, although I think he will sell it direct."
angela jenner on Friday 20 February 2009
"This may well be an idiot question, but nevertheless I will ask! Jeremy - if the process you describe involves such high temperatures for longish periods, doesn't this mean that the compost, which is sterile, is best as a soil conditioner rather than a material which will release nutrients to the soil - ie a bit like leafmould rather than nutrient-releasing garden compost which is made over a period of time with a mix of ingredients? I can never make enough either, but I wonder if adding well rotted manure from a farm would give more to the soil if you want more than just a soil conditioner? I'm interested, as I'm looking at getting some compost from our local green waste site. I need to look at it but it's free!"
Rosemary on Friday 20 February 2009
"Rosemary, I have checked this with The Compost Shop and they have confirmed what I thought: making compost sterile doesn't remove any nutrients, it just kills off weed seeds, pathogens etc. As the input material is all plant based, what comes out has the perfect combination of concentrated nutrients for plants: a good NPK balance with all the required trace nutrients (unlike many non-organic fertilisers which are just NPK). So it is much more than just a soil conditioner (like leafmould) and will actively feed plants over a long time. Personally, I still have reservations about using manure after last year's problems with aminopyralid herbicide contamination - I am not convinced that there isn't some of the contaminated hay 'in the system' or that farmers who supply manure know what their animal feed had sprayed on it. If you can be sure that the manure is from a good source and is well rotted down then it could also provide a wide nutrient source."
Jeremy Dore on Friday 20 February 2009
"Ah great Jeremy, thanks. I'll have a look at our free green waste compost in that case. I wish I owned a trailer. For anyone near Cambridge it's at Donarbon's site on the A10 just north of Waterbeach and is open 7-12 on Saturdays and 7-4 during weekdays. Shut to the public on Sundays. See: http://www.dickersongroup.co.uk/pdfs/Donarbon_directions.pdf "
Rosemary on Friday 20 February 2009
"Very interesting - didn't realise there were large-scale composting sites like The Compost Shop around. Anyone know of something similar in the South of England? We're in Berkshire and could certainly use a large dose of compost to break up the heavy clay soil we have."
Anne on Friday 20 February 2009
"Anne, The Compost Shop regulary deliver all over England, so it might be worth contacting them. I particularly liked being able to order a huge 1-tonne sack of compost which can be recycled, rather than lots of 60 litre plastic bags."
Jeremy Dore on Friday 20 February 2009
"Thank you for operating such a user-friendly site and so full of useful information. Here in the US, we have nothing similar to growveg.com. We also are years behind you re. industrial composting and use of manure. But, as so often happens, we're behind Great Britain just enough so that you folks will be able to perfect both processes before we begin using them on a large scale. I lived in Berkshire for six months in 1997 and traveled extensively during that time, so every time I read your articles great memories come rushing back. A tip of my garden hat to you all. - Clarice White McKenney"
Clarice (White) McKenney on Saturday 21 February 2009
"To find out where you can buy compost in your area try www.compostsuppliers.wrap.org.uk where you can search by type of product and by your postcode to find the nearest supplier. It also tells you if they are certified. Most will sell in bulk either by collecting your own trailer-load (£15 a tonne from my local supplier and they'll load the trailer for you) or in bulk bags (1 cubic metre or approx. 1/2 ton in weight)."
Laura on Sunday 22 February 2009
"Very useful link - thanks for that Laura. For the US, there is a list on the US Composting Council's website at http://www.compostingcouncil.org/programs/sta/participants.php"
Jeremy Dore on Sunday 22 February 2009
"Thanks for the explanation. My council (Stirling) has been providing FREE soil improver (PAS100) for a while. It's made up from the green waste they collect fortnightly from our brown wheelie bins. Last year I made raised beds from recycled wood and used the free compost from the Council. The only thing I paid for was the seeds - perfect!"
Philippa on Wednesday 25 February 2009
"Rosemary, is the Cambridge compost really free? I need loads for my new raised beds and its as close as anywhere in Norfolk"
angela jenner on Thursday 26 February 2009
"Hi Angela - yes, it's free if you collect it yourself and take your own bags. My allotment neighbour got some and he was pleased with it, although someone told him the quality can be variable. He was happy with what he got though. I'm going there this Saturday to get some."
Rosemary on Thursday 26 February 2009
"Brilliant in-sight as to what goes on at one of these huge composting plants. I have a friend who has been to one near our Allotments...somewhere and it sounds magical. Is that the right word? - godness I've become a compost geek! In our case, Carrickfergus, N. Ireland, our council delivers our own collected green waste back to us at the Lottie, composted, for free. However, it did have a lot of mushrooms in it last year and some mould - bit concerned about it's quality (maybe that's why we got it gratis!)."
Carrie on Monday 2 March 2009
"This is exactly the sort of stuff I need for my new raised beds. I'll take a look at the Compost shop site, but does anyone know if any of the local councils around Derbyshire give away or sell there compost that they must all be collecting from homes?"
Dean on Saturday 7 March 2009
"I'm really pleased to have all this helpful information. My local council (Leicester)produces compost from the green waste it collects, so it's local. But THREE TONNES Jeremy?! Being priviledged enough to have seen your garden, where will you put it all??"
Elspeth on Monday 9 March 2009
"Elspeth, Strange as it may seem I have used all but a few bagfulls of the three tonnes of compost on my garden. It doesn't go as far as you think...!"
Jeremy Dore on Monday 9 March 2009
"I bought a couple of tonnes of recycled material in West Sussex which looked good, though I'm no expert. Having planted some tomato and courgette plants plus some runner beans from a packet which all started off well but now are going yellow and dying off. I tested the soil with a kit and it seems neutral, so very perplexed. Any ideas ?"
Rod on Sunday 2 August 2009
"Rod, this does sound strange and is quite difficult to diagnose without seeing the actual plants. I can suggest a few things: 1. If the plants are in containers then it may be that you just need to add some more compost as the nutrients will gradually leech out, or it could be over-or under watering particularly if the containers don't have good drainage holes. 2. If the plants are in the ground then again, watering could be the case. 3. Was there any manure added? If so then please take a look at http://www.growveg.com/growblogpost.aspx?id=42. 4. Finally, I would suggest contacting the source of the recycled material and asking them as it can't be good for their business if this is happening and they should be willing to advise you. Good luck! "
Jeremy Dore on Sunday 2 August 2009
"As an update to this article, I can say that the compost has been of excellent quality and my plants are now (as of August) growing very well - often twice as high as the same varieties of plants grown last year. Plus the compost, being produced at high temperatures, has kept weed growth down - all apart from Mare's Tail which gets through almost anything!"
Jeremy Dore on Sunday 2 August 2009
"Hi, I asked a local supplier about topsoil to lay my new turf, and he recommended recycled compost to me, and said it would be better for my new lawn as my soil is heavy(clay)is this correct?"
mike brindley on Monday 11 April 2011
"Compost is generally the best treatment for heavy clay soils, though I have little experience with turf."
Jeremy Dore on Tuesday 12 April 2011
"I have used the Cambridge (Donarbon) compost for 3 years on my allotment with good results. I even grew tomatoes in it with no other soil. Does anyone know the NPK analysis for this compost? "
David Ellis on Friday 9 March 2012
"DOES ANYONE KNOW OF ANYWHERE IN SCOTLAND THAT HAS THIS COMPOST?"
Anne Edmonds on Tuesday 8 May 2012
"Hi David Ellis, I to am trying to establish an NPK and Ph value for this kind of compost but it seems as though this information is difficult to find!"
Barrie Brock on Monday 2 July 2012
"Good luck Barrie, it seems to me the composters are reluctant to make any claims at all. Like previous writers I,ve had tremendous success with weeds suppression but the best has been the transformation of a claggy clay to a fine loam. At last it seems I can grow carrots and parsnips! "
David Ellis on Monday 2 July 2012
"Thanks for your answer David, I am very interested that you have been able to transform your clay to a fine loam as I have just experienced the opposite results and we are just about to dump the contents of two 2.5 x 1.5mtr x 0.6 high raised beds!! We live just south of Oxford and last year I bought a mini skip load of compost from a company called M and M. The compost looked really good and I dug a 6 inch layer of it into both of my raised beds with some sharp gritty sand and although it made the soil much more friable and manageable at that time I have been unable to plant either of them so far this year. The soil will not become friable no matter what I do to it and when it is in a damp state it behaves just like clay and my neighbour has described it as being 'just like chewing gum'!! So you can imagine what it is like when it dries. yes, it is so hard it is impossible to break down it is just like rock rather than soil. As you can imagine we are at our witt's end and wondering what to do next as I am going to miss the whole season if I dont sort it out. I dont blame the compost as I knew it was a clay soil that I put into the raised bed. It was using up what we had dug out of a bog garden that we were building. However it seems that I have somehow made it worse by adding the compost!!! I have now dug out one raised bed and piled all of it's contents on plastic sheeting to the side of the front drive, thoroughly dug over the bottom to ensure good drainage and now half filled with a better soil that I had from turf that was dug up to extend my other ground level vegetable beds. I have now ordered one and a half tons more compost so I will repeat a digging in of a 6 inch layer of compost with a sharp gritty sand to make a nice light soil so I just hope it works this time as I just dont know what went wrong. I still have the second one to sort out and I have just been quoted £216 for a six yard skip to take it away!! Goodness, I am going to have to grow a lot of veg to get my money back!!! Do you have any ideas where things went wrong as we also like parsnips so well done to you."
Barrie Brock on Tuesday 3 July 2012
"Barrie, We live about 5 miles west of Cambridge and our clay soil is technically called marl. Clay over chalk. We have a high water table on our allotments (which means rabbits are not a problem) and like you I garden on raised beds, all supported by timber frames. When I started (about 7 years ago) I dug the plot quite deeply but drew the line at double digging! As you, probably, I never tread on the beds. However my plot neighbours garden more conventially and dig in their muck and/or compost each autumn but do not use the bed system. I lay a 2-4" layer of Donarbon (council) compost late summer or early spring but rarely dig it in. The worms do that. Last year I forked over the beds that had no compost cover and the frost broke them down, but my best results were on the well composted beds and (he said a tad boastfully) I could prepare my brassica beds using one of those green plastic dibbers! I'd recommend a book "Organic Gardening The natural no-dig way" by Charles Dowding ISBN 978-1-903998-91-5 that explains what to do far more eloquently than me. regards David"
David L.R. Ellis on Tuesday 3 July 2012
"dear sir i m jaffar we need for my country clean so we start one project in all type of waste recycle. we see your project i m satisfy we built same project in my country in india so pleasa help me thank for your truly a.jaffar "
A.Jaffar on Sunday 24 November 2013
"I have just built 2 raised beds about 1 foot deep and filled them about two thirds full with a mixture of manure and grassy straw it dosnt seem solid enough to me to grow veg will it work if I fill the remainder up with recycled compost if so anyone know where nearest place to Barnsley I can get some thanks alan"
alan on Friday 13 December 2013

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