Trench Composting | Gardening Coach

This is a method of Composting which arguably also comes under the category of Growing Methods for Gardeners.

As a compost method, trench composting is like a compost bin or sheet composting below ground. As a growing method, it involves linking it with crop rotation so that the vegetable garden is both worked and fertilised in particular order to maximise crop yield. More on these below.

Trench composting also provides an option to reduce workload by putting the organic matter where its needed in the first place. What do I mean by this? With most composting methods, the waste material is first taken from crop beds. For example, sprout stalks, slug-eaten brassica leaves that are removed before the cabbage goes to the kitchen. These are then thrown into a plastic trug or wheelbarrow to be taken to the composting area, added to the compost bin and left to rot down.

After the relevant time has passed, the mature compost is dug out of the bin and into a wheelbarrow. It’s then transported it to where its needed in the vegetable garden. Once there it’s dug into the soil ready for hungry crops to be planted.

What Crops and Plants benefit from Trench Composting?

This method provides an excellent soil food source for: –

those crops which work hard over a short time, for example peas and beans, pumpkins and courgettes
but also brassicas such as cabbage and Brussels sprouts that stand in the ground for some time
new perennial crop beds
and around fruit trees as a method of providing nutrients at root level without disturbance

The Process of Trench Composting is very simple –

dig a trench about 12 inches deep in the late autumn or early winter
throw in kitchen scraps, spent summer bedding plants, soft prunings, etc
cover with a layer of soil
continue until the trench is full, then top off with soil and leave it to rot down

Alternatively, if you have a large amount of compostable materials at one time, you could make a smaller / shorter trench, not shallower than 8 inches. Make a thick layer of the food waste etc in the base of the trench, cover with soil back to the original level and leave to rot down over winter.

Although I’ve called it trench composting, you can also use this concept for:

preparing planting holes in advance of tree planting
small holes where there is restricted space and new plants are to be added

Whichever way you make your composting trench or hole, it should not be planted on for 3-4 months. There are exceptions to this rule. For example, where it is being used to prepare perennial beds, the organic matter is being used as a slow release or longer term fertiliser and the plants going in are small.

Using Trench Composting as part of your Crop Rotation System

This is often referred to in the shorthand form ‘Trench Rotation’. Trench rotation is a method of incorporating organic matter into your garden as part of your crop rotation. Strictly speaking a crop rotation system should include a fallow year when that part of the land or garden is rested. Traditionally, farmers would let their animals graze on the fallow meadow and the manure would be dug in to the soil.

With trench rotation, you divide the garden into three, which are –

trench composting zone
pathway zone
growing zone
Then at the end of each year or growing season: –
you move the trench zone to the paths
the paths to the old growing zone
growing zone to the filled in trench

By the end of three years, you’ve composted under every part of the garden bed, and you can start the rotation over again.

This does presuppose that you have paths which are made of earth or otherwise easily changed. And that any permanent crops, such as rhubarb, asparagus, strawberries have a separate composting system.

Trenching Between Rows

If you grow your vegetables in rows, or have a cutting garden set out this way then trenching between rows might work for you.

plant the crops as usual
in the space between the rows, dig a trench for the compostable materials
fill the trench as you add materials

The theory here is that the compost will nourish the nearby plants at root level and you won’t need to add further organic matter, or indeed dig any in before planting.
This would work well for peas, beans and the squash family who are hungry feeders. However, you wouldn’t be able to add in catch crops, ie fast growing crops, in between the slower growing plants until the trench was filled.

Trench Composting Pros and Cons

Pros

you don’t have to worry about maintaining adequate moisture levels
turning / aerating the compost is unnecessary
plants nutrition right where they need it: at the root zone
a deeper, stronger root system is developed so the plants will be better able to cope with dry conditions
can be used in permanent raised beds and in the ground / borders
useful if you have a lot of fruit waste in autumn due to making preserves

Some people also add bones and cooked food to their trench. As the process uses a largely anaerobic decomposition this should be fine. The bones are best crushed first and added to the trench when filling it in one go. Speaking from experience, I’m not convinced that a shallow layer of soil would prevent scavengers from digging up any bone residue, so ensure a thick topping.

Cons

it’s not really suitable for wet waterlogged ground
if you have a serious perennial weed problem, you’ll also be feeding the weeds

Although the focus above has been on productive crops, mention has been made of ornamental plants. Consider the benefits of using trench composting as part of the preparation of a new border in autumn and winter. This method also allows a head start in the building of a hot bed.

And although traditionally created in autumn, trench composting works at other times of the year too. Why not try adding lawn mowings and shredded twiggy material to a trench over the summer? This could be a good place to plant those bare tooted fruit bushes and fruit trees come the winter…

For more on how to compost why not treat yourself to our eBook “Compost and Composting”, available from Amazon?

Or you could ask about Plews Garden Coaching Courses and Lessons