It seems like bad form to blatantly take someone else’s blog idea and go off on one with it. On the other hand, it’s presumably the case that you hope your blog gets other people thinking or better still, doing something.
When I read The Propagator’s blog about hot composting on November 7, it got me thinking. For ten days I thought, then I posted a reply asking why he did it. I got a considered reply but in the middle of it were the priceless words “Mostly I’m interested in the process”.
What a solid gold nugget of a remark that is. I’d read the blog and followed the links provided and read what was there and followed more links and read more. I have to tell you I didn’t learn much, not because the information was lacking but because I’ve seen it all before. I don’t have the tee-shirt but I do have the book. Compost, by Ken Thompson; subtitle “the natural way to make food for your garden”.
I’m no spring chicken, I’m getting on a bit. I’ve been gardening all my life and I’ve always had a compost heap and the older I get the less I believe in it. I mean for starters, “the natural way to make food for your garden” is just plain wrong. Nature simply doesn’t stack up a cubic metre of browns and greens in the right ratio, get it up to 60°C for a few weeks then put it back around the plants that need it. People do that. Nature is the unruly teenager that just dumps it all on the ground around itself. In autumn trees and shrubs dump their leaves, annuals and perennials collapse where they stand. A year later it’s all gone and the soil is ready for the next lot. On acid soils it doesn’t break down so quickly and a substantial organic layer can accumulate.
“Mostly I’m interested in the process.” Me too, the how and the why. The how involves bacteria and my admiration for bacteria and their mastery of biochemistry is boundless. Bacteria in compost is pretty low level stuff, they are multiplying and feeding and multiplying some more. They’re breaking down plant material in order to fuel their activities and the process generates heat. I’m a vegetarian, I do the same. Heat is good, it means they can feed and multiply quicker. If the air supply runs out a different set of bacteria can take the breakdown part way but not completely to carbon dioxide and water, so you get aromatic chemicals like methane and alcohol as end products which eventually prove toxic to the critters producing them. Fermentation, I wouldn’t be surprised if there were simple fungi involved in the process too.
Why is just as complicated. Your garden generates a lot of “waste” material, weeds, prunings, fallen leaves, finished bedding plants, outer leaves of cabbages. Leaving it in situ is messy and weeds will often re-root to grow or seed. You stack it somewhere out of the way until it becomes soil like in appearance then put it back. I try not to let weeds go to seed in the garden, the main problem being the seeds drop to the ground and grow, not that they make my compost weedy. I have a few prolific seeders that I allow to self sow, like foxgloves and Aquilegia, but when I cut them down I don’t want any remaining seeds going into the compost and deal with it seperately.
I tend to put most of my compost on my veg plot and the allotment compost heaps are much more productive than the one in the garden. I do get some weeds and self sowers from the garden appearing on the allotment, but most of the weeds on the plot come from elsewhere, often windblown from adjacent plots.
In both the garden and on the allotment I mainly spread compost in autumn. There is bare ground to put it on and it benefits from being protected from the elements in winter. I’m a no-digger, I don’t rough dig in autumn and let the winter break it down; as far as I’m concerned, soil structure is to be encouraged and nurtured and protected, not broken down. Thus there is a requirement to accumulate enough compost for my autumn needs as well as a requirement for somewhere to put “waste” at other times. When I first got the plot I could have done with a big load of compost to get me started, now I have a heap in hand, though it’s depressing to see its volume shrinking before I get to use it.
If there is space though, as for instance when a veg crop is finished and nothing else is to replace it this season, I see no downside to spreading fresh material straight onto the ground. When my sweet corn and runner beans were finished, I cut them at ground level, put them through my shredder and put it all back where it had come from. Except for the corn and beans I’d eaten, everything the plants had taken from the ground went back, much as it would have done if I’d let nature deal with it. There’s no loss of volume or nutrients at all. There are onion sets growing now where the corn was. Green shreddings get incorporated very quickly and turn brown and inconspicuous even quicker. I am fairly certain they encourage worm activity more effectively than well rotted compost.
“Mostly I’m interested in the process”. So I started to wonder whether you could generate the heat with much smaller volumes of compost than the 1m³ that seems to be the recommended minimum. Surely what you’d need would be insulation so that the smaller volume behaved like the middle of a bigger heap. There are lots of compost bins available, almost all much smaller than 1m³, some of them claiming to generate heat. I was looking at the HotBin composter. Alys Fowler wrote glowingly of it in the Guardian. It’s Polypropylene foam and holds the heat in. But it’s £195. Ouch! Its capacity is about 200 litres. “Get rich mature compost in just 90 days, 32 times faster than a cold compost bin” (Really? A cold compost bin that takes 8 years to produce compost is called a freezer)
Actually, I read about the Hotbin, oops, that should be HOTBIN, after I’d made my own. I routinely shred my garden arisings and take them up the allotment in plastic sacks. I measured a full sack and bought a few 450 x 1200 x 50mm sheets of cavity insulation sheet. I cut them in half and made a box with four 450 x 600mm pieces, then cut a piece for the bottom and two for the top. Some strips of wood to hold it all together and I was good to go for a little over £20. I shredded a bag full of aster stems, kitchen waste, weeds and leaves, put it in the sack, put the sack in the box and fitted the top. I reckon I had about 170L in the bag. In a couple of days it hit 31.3°C, then it slowly came down again. By today it was cold. Then I read up about the HOTBIN. It seems what I had done wrong was to cut off the oxygen supply. My bacteria had suffocated. Worse, since I was responsible for creating anaerobic conditions, toxins were probably produced that killed them. I was a murderer. I already felt bad because I’d failed; now I felt guilty too.
I lifted the bag out and transferred its contents into another bag, fluffing it up to get lots of air into it before putting it back in the (airless) box. I muttered conciliatory words to my probably dead bacteria. I did it with my bare hands, as a penance. They still stink, penance indeed. I briefly flirted with trying to pump air in via a tube, but the pre-compost had settled into a bit of a lump, it was never going to work. HOTBIN get around the air thing differently, in that they tell you to add a coarse bulking agent that keeps it open enough to allow air flow. It gets used at a 1:5 ratio with the waste mix. They sell a 75L bag for £16.99. That’ll do two mixes.
When I emptied out the waste mix, it was warm and sweaty at the top but at the bottom didn’t look any different from when it was put in there 11 days ago. It’s back in the box and I plan to transfer it into a different bag every couple of days to see if aeration is the magic key. It’ll have to work pretty darn well to convince me it’s worth the bother.