Thursday, 21 August 2014

A rant about poor compost

As lots of fellow bloggers have been doing recently, I feel I have to draw attention to how poor much of the commercial compost on sale these days is. Even leaving aside the issue of the weedkiller-contaminated compost with which I had to contend, very frequently the compost seems to be completely lacking in nutrients. Plants sown or planted in it can barely survive, let alone thrive. Look at these little cabbage seedlings, which are now a month old:

By this time, they should be at least twice the size, and they should be a healthy green colour, not yellow and sickly like these.

The trouble is that a high proportion of the content of commercial compost is material that has been discarded specifically because it is no good! Local Councils encourage us all to compost plant matter at home (some councils provide free or heavily-subsidised compost bins), and only to take to the Household Waste Recycling Facility (aka Tip) the material that is too big/tough to compost without being shredded, or is diseased. Is it any wonder therefore that commercial compost is poor? Where are the nutrients supposed come from?

This one mentions NPK and trace elements, but significantly gives no indication of how much of each is present. The patented wetting agent is evidently considered the most important feature. I would have thought that good compost wouldn't need an artificial wetting agent.

The blurb on this one has all the right words - "peat-free", "organic", "recycled".

But what are "composted timber residues"? Presumably wood!

How long would you expect your compost to provide plants with the nutrients they need? Suppliers of commercial compost evidently expect it to be a short time, probably because they hope you will then go and buy some of their expensive plant-food to replenish the poor compost, as evidenced by this next photo:

 I have seen some multi-purpose composts say that they provide nutrients for only 3 - 4 weeks. Surely this means that the nutrients are added artificially during manufacture and are easily leached out when your plant-containers are watered?

Until recently, most commercial composts used to contain a fair proportion of peat, but it has become politically incorrect to use peat, because this depletes the ancient peat-bogs, a resource that is renewable only in the very long term. But the fact is, peat is an excellent growing medium for young plants. Look at these words "...contains higher levels of peat for a better, more consistent growing medium..."

This puts gardeners in a difficult position. You have to see it in context though: we extract huge quantities of oil and gas from the earth and people seem to consider this to be OK - even "essential" - so how does this differ from extracting peat? What proportion of the population even know what a peat-bog is, let alone considers it essential to preserve? Using peat for growing plants doesn't pollute the atmosphere like burning oil does either.

August 2014: seedlings in 3" pots of multi-purpose compost

There is definitely an opportunity here for an enterprising company to develop compost that does have a good level of nutrients, does not contain peat, and does not consist mainly of discarded household rubbish. What happens, for instance, to all the fruit and vegetables that are rejected by the big supermarkets as being sub-standard or surplus to requirements? We are told they are "ploughed into landfill". Could they not form the basis of organic compost? What about the husks from maize and sweet corn, consumed in vast quantities by people all round the world? Could they not be used for making compost? There must be lots of things like this that could be used, if only someone thought about it. Anyone know an entrepreneur...?


  1. The worst of it is that once you find a decent enough compost, you go back for another bag and it's completely different from the first bag you bought, it just isn't consistent from bag to bag so it's a lottery each time you buy compost whether it's going to be good or not. I think it's a case of feeding, even after a short time, to know that the plants are getting enough nutrients.

  2. Having only mad my own for a few years, I would be reluctant to go back to commercial. Save the peat for making whisky! Coir may be a viable alternative but it is not always available in sufficient quantity.

  3. I think the problem with commercial compost is not necessarily the lack of nutrients, the nutrients are there, the problem is that the stuff is dead. Healthy soil is full of life, commercial compost is made so hot that it kills all the microbes, either bad or good, and it ends up so dry that they need to add those wetting agents. Many of the microbes in healthy compost work symbiotically with plant roots to make nutrients more available to the plants. I don't know if you have them available in the UK, but I always add an inoculant or a fertilizer that contains live mycorrhizal and bacterial inoculants to my bagged potting soils, it does make a difference. This whole topic, the life in the soil, is a very interesting topic to read up on. I'm certainly paying far more attention to the health of my garden soil, not just potting soil, and I think it has made a real difference in the productivity of my garden.

  4. Great post Mark. I am one of those bloggers that have recently been saying how much available compost nowadays is absolute rubbish.
    We have a waste recycling plant up the road. Many of these facilities are just a way of local authorities avoiding land fill tax- which is huge!
    You should see all the lorries loaded with waste wood as well as prunings of course that go into this stuff.
    I have actually supped with devil and accepted free loads that make a great mulch! I would never used it as a compost!

  5. I'm keen to give bio char a go next year though it is more expensive I think if it gets the plants off to good start then it may well be worth the investment.

  6. My tomatoes grown inside the greenhouse in compost, have failed this year and I have been feeding them, I agree we are being fobbed off. I have to use containers for veg in my garden and this year has been poor all around. Your post was brilliant and highlights the problems, do the manufacturers think we gardeners are daft!

  7. As wood decays it actually depletes the nitrogen in the compost and also the new composts do't seem to absorb water as much hence the water retention additions.. I winder how much more environmentally friendly it is to ship coir round the world

  8. Sorry to jump in again Mark,but I forgot to support your comments about peat.
    I think you might have read my recent post about using soil to make compost and know that I do not have to suffer buying compost at all but should I do so - and I used to buy plenty of multi-purpose peat compost- I would be looking for peat based compost. For me 'peat-free' as a sales boost is a complete turn off and says to me "don't buy this"
    If any readers would like to read a brilliant exposition of why peat is good for composts and why it is NOT IMMORAL or environmentally irresponsible to use it follow this link
    I know it won't come through live (Don't know how to do it!) but there is enough there to google it- glendocik peat to find a very stimulating read

  9. I think it is very important to highlight this as so many people are unhappy with the compost they buy. I have had various brands this year but wasn't happy with any one.
    Does anyone feed back to the companies producing it? Sadly I can't remember what I bought in spring as I don't keep notes but I would consider keeping records next year and telling the companies concerned.
    I also, would question the sense of shipping coir round the world.
    My tomatoes have not been as good as usual this year and I have grown them in the same way as usual so could it be the compost? The weather, which we can often blame, has been great.

  10. I don't know what I'd do without my source (Vermont compost company). Since I found it, I never use anything else. It is a pain to get, but my seedlings grow faster and healthier than any I've had before even my own. I've been using for about 5 years now. But then it is really just a regional seller and you won't find it at any big box store.

  11. I've noticed that the quality of compost this year has been really bad. My seedlings have really struggled compared to previous years. I've also noticed it drying out a lot quicker.


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