Hotbin classroom by Omnibus - my lessons learnt (do add yours)

[Omnibus]

After having done standard composting for most of my life I became disillusioned with compost I managed to produce so this January bought a 200 L hotbin.

I decided to record temperatures on more or less a daily basis in order to work out how best to operate the unit (date, time, ambient temp, lid temp, heap temp, valve mm, ullage and comments). I only really use the temperature from the loose thermometer, the lid temperature can be 5-20 degrees lower.

I knew from the start that it would be important to have a good mix of green and brown waste to compost. To ensure there is a constant supply of material I have three large containers to store 1) twigs and cut woody bits 2) greens 3) leaves and browns.

With the help of the starter bottle filled with hot water the hot bin got going quite quickly and worked well at 40-50 degrees over the winter period. I first removed my first lot of half-digested compost in early March.

This first compost was good for mulching. The Hotbin continued at similar temperatures until mid April at which point the normal internal temperature became 55–65°.

I had noted the high moisture content of the mix I was using (which included grass cuttings to get a quick temperature increase), so I have been using torn cardboard to control that.

I have not used any of the standard bulking agent provided with the hot bin, instead I have used Woody material from the garden which I need to compost anyway as I don't want to use the councils green bins and also I want the maximum quantity of compost. I have found it quite tricky to get the right balance of materials composting, but generally as long as the twigs are cut reasonably short and are allowed to dry out before being composted, the bin can function well without any intervention.

That said, in practice I have found that the bin is not large enough to process all the green and brown material being produced over the summer period. I have therefore had to remove compost from the bottom of the unit before it has completely finished. I need somewhere to put this to complete the composting process for which I use a Dalek-shaped 300 L compost bin I bought from the council.

I have found a problem with air circulation slowing down the process and also on occasion leading to anaerobic decomposition. If the problem is mild, then I simply use the rake to loosen up all the top layers of the unit to let the air in.

[Omnibus]

If your bin should be hot, but is not, try this.

I find a problem with restricted air supply when the lower layers get compacted. This is awkward if I am not ready to take anything out from the base.

I have tried mixing up the heap but it is too difficult and takes too long so I thought I would try another approach.

I have a 1cm diameter steel rod with a ball on the top that came from a garden centre. I measured the distance from the interior bottom of the hotbin to the lip then wrapped two bits of sticky tape around it with a 1mm gap between to mark this distance less 3cm from the bottom. Using this as a tool I make 9 or 16 holes in the compost (except for the last 3cm, of course) by pushing the rod firmly down, taking great care not to push too far!

The idea is that this creates enough air circulation to oxygenate the entire heap.

I have tried this method three times, the first I used a garden cane, this worked well but I felt it was dangerous as the cane could break when forcing it down and could badly injure my arm. The second time I used a 5mm steel rod but this did not seem to have much effect, probably it did not make a big enough hole. The third time was two days ago, the heap was an uninspiring 45 degrees (interior) and on a downward trend. I made 9 holes with my 1cm rod which took about 2mins. The next day the heap was up to 56 degrees, I filled the unit up with Jasmine cuttings and twigs. This morning it was cooking fast at 65 degrees, a bit higher than I normally like but useful for now as I have a lot of material to compost!

Note: My Hotbin is in a shady and cool part of the garden.