If you haven’t heard of trench composting, it’s just what it sounds like – you dig a trench in the ground, add organic material and then pile earth back on top.
Typically you leave it around a year (or plant some cover crops on top of it) while microorganisms break down the material and incorporate it into the soil, and then plant regular crops on top of it.
It may not be the most efficient or fastest way to compost, but it works, it enriches the ground and it’s particularly good for smellier items like meat, dairy and fish.
But what about people who don’t have a garden? Could they replicate the mechanisms of trench composting – in a pot?
If it’s possible, it could be a great option for people who want to compost in small spaces, or who live in an apartment with a balcony.
I’m fairly sure it’s feasible, but to be sure I’m running an experiment.
The steps
I started by gathering some weeds, tired spinach and chard leaves and kitchen waste.
Because of some old soil in my weed bin and some kitchen papers, there’s a good mixture of greens (high nitrogen) and browns (high carbon) materials in the mix.
I roughly chopped them up with some shears – I would have liked to use my strimmer, but realized I hadn’t mixed up any fuel for the year ahead. (As I write this, it’s the 1st March, and the heavy gardening year hasn’t really started.)
I also had some biochar and ash lying around, so I added these into the mix.
Both biochar and ash have multiple benefits for regular composting. For example, biochar improves aeration, retains nutrients, and reduces odors, while ash helps with aeration, minimizes nitrogen loss, and speeds up decomposition.
I can’t be sure they’ll make a difference here, as they are not commonly used in trench composting. But I want to give this experiment every chance of succeeding.
Next, I added several inches of soil from my garden to an appropriately sized pot. It’s from the surface level of my vegetable patch, and it’s compost rich thanks to regular mulching. I noticed a few worms in the soil I added, so it should be rich in microorganisms.
I then poured in the material:
added more soil on top:
and I was done.
I’ve put the pot in my polytunnel for now, as it’s still cold outside and the extra warmth may help the breakdown process.
What could go wrong?
It could get smelly, especially as there is a little bit of cooked food in the mixture.
However, I’m hoping the ash and biochar will help with this, and the layer of soil should act as a biofilter.
Mice or rats could dig into the mixture.
This can be a problem with trench composting when the trench isn’t deep enough. This is something I’ll need to keep an eye on.
If I see any signs of this happening, I’ll need to cover the pot.
It could dry out.
I’ll need to keep an eye on it, especially while it’s in my polytunnel, and spray with water if needed.
Decomposition could take a long time.
When I’ve experimented with anaerobic (without air) composting, it’s taken a (very) long time for materials to break down. However, I’m not convinced trench composting is completely anaerobic.
That said, the pot already has holes in the bottom. If I prop the pot up on some stones, I should ensure there is some airflow. What’s more, the biochar I’ve added should help with aeration.
What next?
I anticipate it will be some time before the process is complete – maybe even a year!
However, in the meantime I expect to see the level shrink, and maybe some signs of decomposition.
So it’ll be a while before I know if the experiment is working or not – I’ll update with progress (or setbacks!) as they happen.
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