Trench composting systems are effective for provide compost to rows of beans, marrow beds etc. etc or as a rotation system to compost the whole garden over a period of years. Alternatively,
individual holes can be dug where space allows in the garden. At the simplest level a spade or post hole digger can be used to make an 8-12" deep hole the width of the hole can be varied to suit the volume of waste which should be at least 4" deep
in the hole.
In-ground trench or pit composting provides a simple way for composting fruit and vegetable waste including uncooked kitchen scraps. Techniques that involve burying the organic material have the
advantage that no special equipment is required and once the material is buried there is no visible evidence that composting is being undertaken.
As decomposition in underground composting happens more slowly
than in the more usual bin systems it. is perhaps more important than in normal systems to expose the maximum surface to microbial activity. Cutting the waste to about two inches in length is recommended. The green and browns can be mixed in the
pit using a fork of spade, but I find it is easier to mix them before adding to the pit.
One of the concerns expressed by people new to trench or pit composting is that it will attract rats and other animals
looking for a free meal particularly if it is left when only some of the waste has been added and it is not yet covered by the four-inch layer of organic material. The waste in the pit can be covered with a thinner layer of soil and the whole pit
covered by a sheet of plywood. Once the waste material reaches the depth of four inches the pit should be filled with soil.
If the material is kept moist (it may need watering) it
should decompose in about a year after which the area can be planted.
Pit composting (see below) is suitable for an area where there is limited space either because the garden is small or is
permanently planted areas such as perenial flower beds.
Trench composting is usually used in the vegetable garden so that composting can be started in the late summer or autumn with the trench being filled and ready for
spring planting of runner beans, french beans or peas.
Trench composting can be started earlier, if space is available on the plot, so that chopped brassicas stalks can be included as this offers
an easy method of composting the stems which may be slow to compost in a conventional compost bin. Trenches can also be dug between rows of plants or seeds
A similar method where circular pits are dug, rather than
a trench, can be used for courgettes and pumpkins.
The trench is often dug for convenience about a spade width and depth the length of the required bean row, which might be across the width of an allotment plot.
It is worth checking the recommended planting distance for the beans as; if a double row is required the trench will need to be wider.
Place the soil along the side on the trench so that it may be used to cover the composting
material as it is placed in the trench. Start added the waste at one end of the trench covering it with the soil as it is added. Some people dig a deeper trench so that a second layer of waste can be added but this will depend on the quantities of waste available
and the number of rows of beans to be grown. When the waste has been covered the soil is likely to have made a small mound along the length of the trench but this will settle by the time of planting. I would suggest marking the trench with small sticks so
the it can found in the spring when you need to plant in it.
Some gardeners use trench composting as part of a composting rotational system where the trench is moved across the garden each year.More information can
be found at