If you’re looking for one of the simplest ways to compost, you’ve stumbled across the right method here!
Trench composting may involve a bit of digging, but it requires little thought about anything else.
It’s also a great way to improve soil fertility – but it does come with some downsides, which we’ll come to later.
What is trench composting?
Trench composting involves digging a trench or hole, dropping in organic matter and covering it up with soil.
Most sources will tell you that is an anaerobic (without air) composting method.
The idea here is that because when air is cut off by the soil, anaerobic bacteria break it down. This is a slower process than aerobic composting.
It seems to make sense that anaerobic composting would take place, but I also suspect that a lot of the breakdown is by microorganisms and physical decomposers in the soil.
It’s also possible that some oxygen is provided by the soil.
Six Trench Composting Methods
Simple trench composting
What you need:
- (Optional) Mark out where you want the trench to be with string.
3. Put organic material in.
4. Cover with soil.
5. Mark where the trench is so you don’t forget!
Watch the short video below to see just how quick and easy this composting method is!
Deep trench composting
Deep trench composting does exactly what the name suggests. It’s a deeper trench, and usually involves layers being built up over several weeks.
Here’s how it works:
- Dig a trench in your soil. Aim for at least 18 inches, and up to 24 inches. Do this in daylight hours, just in case your neighbors think you are burying a dead body 😉
- Traditionally, you then add food scraps. However, as we’ll see you can add most organic materials. You can also balance this out with higher carbon materials such as leaves and shredded paper.
- Add an inch of soil then put a barrier such as a pest-proof mesh on top to stop pests.
- Continue layering until you have nearly filled the trench.
- When there are just a few inches left, fill in the soil until the trench is full. The add some more soil on top to allow for settling.
The English Method of Trench Composting
Also known as the rotating method of trench composting, the English method involves dividing your plot into three strips.
One strip of soil is used for trench composting, one for paths and one for planting. The strips are then rotated each year.
Here’s how to do it:
- Divide part of your vegetable garden into three strips. One will be your trench, one will be your path and one will be for growing in.
- In the first year, fill the trench with food scraps and other compostable materials as usual. Use one of the other strips for planting and one for a path.
- In the second year, convert the composting trench to a path, the planting strip to a composting trench and the path to planting.
- Repeat the process in the third year.
Check out the infographic below to see an illustration of the method.
Pit Composting (Dig and Drop)
Pit composting is simply the process of digging a hole in the ground, filling it with waste material and then covering it with soil again.
It follows the same principle as trench composting but is even simpler.
However, it does help if you remember where you have dug your hole!
Worm trench composting
Worm trench composting involves digging a trench and adding food scraps and other organic material.
You then add worms (or worm cocoons) to the trench.
The worms consume some of the organic material, helping to speed up the decomposition process.
See Red Worm Composting for a detailed description of worm trench composting.
Raised bed trench composting
- Cut down and put aside plants at the end of the growing side.
- Dig a trench across the whole length of the raised bed, putting the soil aside.
- Place cut-down plants in your trench.
- Add any other organic material you have to hand.
- Replace the soil.
Some raised bed gardeners take all the soil from the top of their beds and put it to one side.
I helped a friend. do this recently – we removed the top compost layer and replaced it with manure.
As I use a No-Dig method, and simply added a layer of compost to my bed the previous autumn, it’s going to be very interesting to see who gets the best tomatoes this year!
For a more in-depth guide see Farm Life’s guide to trench composting in raised beds or check out the video below.
What to put in your trench
You can generally be pretty free and easy with what you add – after all, the whole point is for simplicity.
That said, it’s a good idea to add both high nitrogen and high carbon materials if you can, and there are some organic materials which you should best avoid.
|High nitrogen materials (greens)||High carbon materials (browns)||Materials to avoid (or dig deep and/or cover with mesh)|
Weeds (without seeds)
You can find many examples of high carbon and high nitrogen materials in our Carbon : Nitrogen ratio tables.
How good is the compost it makes?
Anaerobic composting can create compost that is lower quality than aerobic composting.
However, gardeners usually find trench composting usually provides great results.
There’s little research, but one Indian study did report that trench composting produced compost with more nutrition than surface composting.
I haven’t been able to see what type of surface composting the researchers used. However, Khalida et al also argue that more nitrogen is retained in trench composting than in surface composting.
Tips and tricks
Heap the soil higher over the trench
Bear in mind the material in the trench will sink over time.
With that in mind, it’s a good idea to heap the soil a little higher over the trench than it is on each side.
Cover the trench with mulch
After the trench is full, cover it with mulch or a layer of leaves to help retain moisture and prevent weed growth.
Cover pits with wire or a stone
Pits are easier to protect than trenches because of their smaller size.
If you have buried any smelly materials, consider covering it with a barrier to stop pests.
Use a post-hole digger to create a line of pits
A post-hole digger can be an efficient way to create lines of pits in a vegetable patch or garden.
This saves the work of having to dig a pit (and remember where they are!) each time you have material to compost.
Shred materials before adding them
Materials break down faster when they are cut up or shredded.
Sow a cover crop
While the normal advice is to wait a year before sowing, some trench composters do sow a cover crop.
This has the advantage of reducing weeds and helping to reduce water loss. It can also help the beneficial fungi in the ground.
Depending on what you plant, you might also get some food out of it!
Five advantages of trench composting
Viable in more places
Incredibly, in some places traditional composting is prohibited.
In these places, pit composting is ideal, as it keeps organic waste out of sight (and mind) and runs little risk of odors.
Little equipment needed
Other than a spade or fork (which you probably have already) you need very little equipment to dig a trench!
You certainly don’t need to invest in compost bins.
Traditional composting is not difficult, but you do need to include a roughly even mixture of high carbon and high nitrogen materials, ensure the bin or pile is aerated, and keep an eye on moisture levels.
It’s still a good idea to include both carbon and nitrogen-rich materials in a trench if you can, but other than that, the process requires little thought and zero maintenance.
Reduced water usage
Hot, dry climates can be challenging for composters, as the compost can dry out.
However, when the material is covered with soil, water loss is minimized, and you do not need to add water to the compost.
Traditional composting can cause bad odors if it is not managed correctly, or if an anaerobic composting process is used.
However, by covering material with soil you usually eliminate all unpleasant odors from the composting process.
Six Disadvantages of trench composting
Impact on the soil
Much of the benefits of compost do not come from directly feeding the plants.
Instead, the compost improves soil structure and feeds a network of fungi.
These fungi extract nutrients from the soil and channel them to the plant in exchange for…
However, you disturb the microorganisms in the soil when you dig, which is why no-dig and no-till methods have become so popular in recent years.
May produce methane
Anaerobic composting releases huge amounts of methane.
In fact, methane is a big part of the reason we are encouraged to compost for environmental reasons.
Aerobic composting does release some gases – that’s unavoidable – but it releases far less methane.
Still, as discussed earlier, not every source agrees that anaerobic composting takes place in trenches.
Time and space required
While you are trench composting, you can’t really use the space you are composting in.
Anaerobic compost takes longer to decompose, and fresh compost can be high in phytotoxins, which can damage plants.
What’s more, when it’s full, the ground tends to sink as the material decomposes. (You can partly compensate for this by adding more material.)
The general advice is also to leave the space for 6 months to one year while the material decomposes.
I’ve never done this, as I’m too impatient and space is too valuable, and I’m prepared to sacrifice some crop quality in order to fully use the space I have available!
Still, in contrast, aerobic composting takes place outside the vegetable patch.
If you are using a bin, it’s a very efficient use of space and allows you to ensure that your veg bed is being fully used at all times.
So if maximizing the amount of space available to you is more important than the ease of composting, I’d suggest using a compost bin instead.
Pest control (depending on materials used)
By putting soil on top of smelly material, you should avoid attracting larger pests.
However, my experiments with pit composting suggest that when items like meat or fish or added, animals can detect them and dig up the food.
If you do add smelly materials, consider digging deep and/or covering with a barrier to stop pests.
Hot composting processes – and some anaerobic composting processes – kill weed seeds.
However, when you dig weeds into the ground, any seeds attached to them could re-sprout in the future.
If you really don’t want to think that hard about composting, trench composting might be the option for you!
Limited research – but lots of experience – suggests that it’s an excellent way to improve your soil, and may be more effective at retaining some nutrients such as nitrogen.
On the other hand, if you want to maximize the use of space in your garden, you may be better off with a compost bin.
Of course, there’s no need to limit yourself to just one type of composting!
You might also find it worthwhile to experiment with different types of composting, finding out which ones suits you and your soil!
How long does trench composting take?
That’s always a matter of debate – although typically composters will tell you six to twelve months. The truth is it depends on a number of factors. These include:
The material you use: Woody materials take longer to decompose because of their high lignin content.
The size of the material: Large pieces of material take longer than smaller pieces of material.
What you are growing above the trench: Some plants are more tolerant of decomposing material than others (think of the plants you see growing in your compost pile!)
Can you compost pet waste in a trench or pit?
Yes, you can. However, the Compost Education Centre advises not doing so in vegetable patches, and limiting trenches and pits for pet waste to ornamental beds. This is to avoid pathogens infecting your vegetables.
Can I trench compost in the winter?
You can usually trench compost in the winter if the ground is not frozen. When it freezes, the ground is usually too hard to dig.
It may also take longer for the organic material to decompose due to the colder temperatures. However, some composting does still happen in winter, and the layers of soil could help protect the organic material from the extremes of cold above the soil.
You can speed up the process by insulating the trench with straw or other organic material.
Can I trench compost in a container?
Yes, you can trench compost in a container, such as a large pot or bucket. Simply fill the container with organic material and soil, and then cover it with a lid or mesh to prevent pests from getting in.
Can I put plants in a container when I am trench composting with it?
I’ve tried this myself. It’s not ideal, as the soil or compost sinks down as the material decomposes. However, it is possible.
Can I use trench composting to compost large branches or tree trunks?
My own experiments with branches have shown very poor results. That’s probably because branches take a long time to rot down, and a large amount of wood can rob the soil of nitrogen.
However, there is a rather more specialized form of composting, known as Hugelkultur. This usually involves building a large bank with wood/logs e.t.c. and covering it with organic material and then soil.
While a bit more complicated than simply digging a trench, it can have good results in the long term.
Compost Education Center Trench Composting