Wednesday 10 February 2016

Contemplating compost

The limited action of adding nitrogen to activate a compost heap

A holiday postcard from Funchal
Sometimes you learn something that truly astounds you. This research review is dated 2008. I am grateful to Robert Pavlis on The Garden Professor's Facebook website for bringing it to my attention. It is real serious science that brings together sixty separate investigations.

It is common knowledge that adding nitrogen in the form of a fertiliser or as a nitrogen rich manure activates and speeds up the rate of decay of garden compost. It turns out that this is only true of soft vegetation - which is the stuff that decays rapidly anyway. The rate of breakdown of the fibrous stuff such as straw or herbaceous tops or woody prunings is not effected in anyway other than adversely.

The technically minded compost buff talks about nothing other than carbon/nitrogen ratios. Soft stuff such as young weeds and fresh mown grass might be twenty to one carbon/nitrogen proportion. Herbaceous tops are perhaps seventy to one and are very slow to decay and this is generally explained as a result of low nitrogen content. Thirty to one ratio would seem to be optimum.

It might take several years to turn fibrous material to compost. 

Here in the 200 year old  Blandy Garden, time scarcely matters when they eventually dig out wonderful fine stuff

They compost all the organic material they are collecting
Regular readers will know I do not have a conventional compost heap! I know one of my gardening heroes writer Ken Thompson writes that he needs to have a 'serious conversation' with anyone like me! I protest that I recycle all of my organic matter albeit directly.

I never have weeds to remove as they desiccate in situ after spraying with glyphosate, hand pulling or hoeing. All my mowings are scattered by my mulch mower. The worms bury my leaves and the toppings and tailings on my vegetable patch. Most of my dead herbaceous tops are shredded into little pieces by my  hedge trimmer and left on the ground. I bury newspaper and sometimes wood or woody prunings. My bulky prunings are burnt in such a manner to create masses of everlasting charcoal.

The nearest I come to composting are heaps of herbaceous tops from areas of the garden supervised by tidy Brenda or tops too bulky to shred and perhaps organic debris from my ponds!
On such piles I have generally flung a little general fertiliser to 'improve' the nitrogen ratio. It would appear I have been wasting my time. Well perhaps not entirely as the organic matter will retain the added nutrients for the future and the soil below will beneficially absorb them.

In Funchal Botanic Garden they bury their tough organic matter
Peter Williams is a very keen composter and he is preparing an article for me on how he goes about the process. Now that will be really interesting.
Robert Pavlis noted on Facebook that it was only he and I that had taken any notice whatsoever of Robert's own startling revelation. The impact of this knowledge seems to be one of deafening silence.

What is the significance to gardeners?
Probably very little. Good composters will continue to mix together high and low nitrogen containing material to the benefit of both. Or even all three if you include the happy composter himself!

Gardeners will continue to compost low nitrogen fibrous material  and such things as privet hedge clippings. After all although it takes much longer to decay, such vegetation makes the most valuable and long lasting soil organic matter and, dare I say, humus!
Gardeners like me will be happy for still fibrous material to be mulched on their soil. My gardener/botanist friend Mike, will continue to re-compost his incompletely decayed fibrous vegetation a second heap around.

I wonder what Peter will say in his post about proprietary  'compost activators'. Are they just useless or merely a complete waste of time?

Links to further reading
Robert Pavlis wrote about organic gardening and glyphosate.
The Garden Professor is having a spot of bother
Ken Thompson has been composting tea bags although Harry Kennedy points out that they should not go into worm bins.
Robert Pavlis is dubious about egg shells although Tony Cuthbert isn't
I wrote about burying wood

You might discern that I have just returned from two weeks in Madeira. I will be showing rather more floral pictures soon!

I expect at our Eden Mar hotel the weed goes in the bin!


  1. A thought provoking blog and links. We had an enjoyable holiday in Madeira a few years ago, in May when the flower festival was on, wonderful.

    1. It was the carnival when we were there. It was too late for me, I was in bed!

  2. Useful information. I must say that the times I tried adding nitrogen to the heap to speed up the braking down process, I did not notice any difference.

    1. Nor have I Alain.
      When i think about it I might have put this post in my myth series. I will call it a myth in my theme column

  3. We have recently changed to a mulching ride-on mower and one of our concerns was that the reduction of grass cuttings on the compost would make it slower to decompose and the volume would be much less. In fact we haven't noticed much difference in rate of composting or volume produced. We still add a bit of urine and plenty of water as dryness is often a cause of a "stalled" compost. We do shred most of the material that goes on the heap with a large shredder and that breaks up all the twiggy bits exposing the internal fibres, without a doubt this speeds up the process. Shredding also mixes the different components which also helps speed up composting.

    1. Thanks for your insights Pauline. I think you will enjoy Peter's article

  4. As you know I also compost like you. Too much work haling it to a pile.

    A number of years ago I went on holidays, and my mother, a good gardener herself cleaned up the garden picking up the dropped plant material. When I got home I was greeted by two big bags of the stuff. What to do? I just spread it back around the garden where it belonged. She was not amused!

    1. Nice story, wayward son!
      Although I would probably do the same myself I might have waited for her to return home!


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