Wednesday 10 April 2019

More on hot composting

Ready to go
Picking up on Peter

I think Peter Williams’ recent article on hot composting was a major contribution to the literature on making garden compost and what you do with it. It was a long article and some of its content is worthy of further examination - in particular to answer any digs at my own methods. These of course are just part of the friendly rivalry between us.
You might have twigged that the John McEnroe quote ‘you cannot be serious’ in Peter's title was my own repost to the very idea of all that effort. I have teased before that some gardeners live to make compost.
Regular readers will know that although I do not usually make garden compost I do recycle all my organic matter - whether by letting weeds desiccate on the surface, letting leaves and debris lie, mulch mowing, burying small prunings and newspaper, and burning waste wood to make charcoal. 

Unlike Peter, for me, nothing goes in the municipal green bin.I was surprised that Peter claims to put weeds in the said bin. The truth is that his weed control is nearly as good as my own.(In some cases it is my own - I have an arrangement that he does handyman work for Brenda and in return I spray parts of his garden). It is probably only perennial weed from distant fringes that Peter so cycles.

Look how hot it got
Peter’s own figures of the very high temperatures achieved in his heap is evidence that all weed seeds will be killed - such as grass seed inevitable in his mowings - and other than perennial weeds he could safely include weeds when making compost.
He did mention to me that the only weed seed that emerges from the compost he makes are those blown in on the wind

Peter made an aside about how in natural woodland an organic layer forms and goes on to explain that this does not happen in gardener’s soils which are mixed by cultivation. To an extent organic layers might develop in his own wood when he mulches on the surface. He mischievously suggests that less mixing might occur in my own no dig garden.
I adamantly declare that my huge population of earthworms ensures this is not so and for me this is a very good thing (His own acid soil might reduce worm populations)

Readers might be aware that in some natural landscapes, especially in the USA, introduction of earthworms is a very bad thing. In such places native vegetation better survives in undisturbed unmixed soil.

A fascinating aspect of Peter’s explanation of decay is that it is not just a breakdown process but also one of building. Most raw compost ingredients as part of their complex journey becomes a bacteria, a fungus, an insect, an arthropod, a worm or whatever. Often several in turn.
I loved his Walter de la Mare quote about Miss T - everything she ate ‘turned into Miss T’ . He tells me that in his microbiology degree finals a complete paper asked him to explain the significance of the poem to the microbiologist. Oh for such subjectivity in education now rather than soulless unchallengeable objectivity

Peter correctly states that speed of decay is more rapid when the carbon/nitrogen ratio of the compost ingredients is low. Most gardeners including myself are in accord with the idea that adding nitrogen nutrient such as urine speeds decay.
I am somewhat embarrassed about this as I did a post based on very credible research that adding nitrogen fertiliser does NOT increase the speed of decay of compost ingredients such as strawy material which starts with a high carbon/nitrogen ratio ( - as opposed to getting a favourable ratio by mixing varied ingredients). Ah well you can’t win them all. No wonder we have so many gardening myths.

I have been burying newspaper for more than forty years
Peter mentions that the wide carbon/nitrogen ratio of paper and cardboard gives it an extremely low breakdown if added to a compost heap. I can certainly vouch for this and some of you will have read my post about burying reams of newspaper for long term water conservation. It hardly breaks down at all and a decade later you can still decipher the print. Be careful what you bury!

Geeky stuff

Pure pleasure
I confess to editing out Peter’s thoughtful theory about the ‘dark’ component of photosynthesis proceeding in his mowings - now quoted. His post was getting a bit long! I have not been unafraid to quote speculative stuff such as my friend Alan Warwick’s theory about how water gets to the top of very tall trees or my own sympathy with Eugene McCarthy’s suggestion that pigs might have a place in our very early ancestry. I find Peter’s hypothesis is pretty plausible. 

“Freshly mown grass cut in summer heats up surprisingly quickly and this has always intrigued me. If the grass box of even a small mower is not emptied, the temperature will rise to approximately 40 C in just a couple of hours. The same goes for grass cuttings tipped into a storage bay. The high temperature is only short lived and falls to the ambient air temperature in a day or so depending on the size of the pile. What I find intriguing is why the clippings heat so rapidly. Even accepting that the cut grass leaves will be coated in microbes, I would not expect decomposition or fermentation processes to occur so rapidly and almost without a lag phase. I have wondered whether this initial temperature rise is due, at least in part, to the ‘dark’ or enzymatic reactions of photosynthesis that must be occurring very rapidly in full light in summer. The temperature rise of stored, cut grass is noticeable lower in winter. This might simply be because the ambient temperature is lower or just perhaps, because in the dim (i.e. low intensity light), short days of winter, the ‘dark’ reactions of photosynthesis are progressing very slowly. Perhaps I will investigate this phenomenon as a small project. (As a preliminary experiment, I mowed an area of grass early this week (January) and deposited it in an empty bay. There has been a negligible temperature rise)”.

In Peter’s discussion about how he uses his compost he casts doubt about the water conservation reputation of mulching with compost. Although he works his away round to conceding that the overall effect of organic matter is to conserve water he casts doubt about the benefit of an ultimately dry layer of water absorptive stuff on the surface. In dry spells it keeps rainfall out - at least until roots grow into it, which when wet they surely will.

Even light showers filter through
I have long thought mulching is overrated for water conservation when the mulching material itself is water absorptive. I have written before how in contrast gravel, small stones or unsealed paving are superb for water conservation and repeatedly act like one way valves for water from even very light rainfall through long dry Summers."

Compost as an ingredient in compost!

I am sure this garden compost would make very fine potting compost
Apologies to our friends over the water. In English english compost has two meanings - that from a decayed heap and the stuff used as a mix!
A renowned USA scientific gardening blog professes that for reasons of hygiene the first should not be used to make the other! Absolute rubbish. (I mean the concept not the compost). Peter has no problems whatsoever with the wonderful stuff he mixes (although I did overlook he uses peat for his seed compost).
After all in Victorian times compost and compost were one and the same!

My own tomato compost is made up from homemade charcoal and soil 
If you have not read Peter’s clear thinking you must do so now. I do not propose to stop making my own seed and potting compost with my own sandy soil and often my homemade ‘charcoal’  and I will still attempt to recycle my garden debris in situ but I have suddenly become sensitive to Brenda’s constant complaint (and I am sure Peter’s private opinion) that my garden is scruffy

Those who have seen my huge herbaceous borders in Summer are shocked by the mulched debris in March
I have no problem with my buried newspaper having a wide carbon/nitrogen ratio. I don't want it to decay

If you missed Peter's article on hot composting go to it here

I was pleased about my article on nitrogen fertiliser failing to speed composting - even though it fell on deaf ears and my original source completely forgot he had ever mentioned it!

My own tour de force on mulching


  1. > gravel, small stones or unsealed paving are superb for water conservation

    I can believe it, but does the gravel make weeding much more difficult, since you can't get below the soil surface?

    �� I really enjoy your blog, by the way!

    1. You need to read my post about mulching and my writing elsewhere teuth1
      You might ask a similar question about all kinds of mulching
      The normal theory is that mulch mats, thick gravel or paving control the weeds from seeds themselves and there is an underlying assumption that perennial weeds have been eliminated before mulching.
      For me the thickness of gravel or stone is of no matter because I control weeds with glyphosate - they are sprayed and wither and die - as should be the case for a no dig gardener.!
      If you don't use herbicides you are down to hand weeding and relying on the fact you completely killed perennial weeds at the start

  2. Sounds like a great thing, but I can barely maintain my cold composting.


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