Everyone is agreed that compost is good for your vegetable garden. Where people differ is in:
1. What they consider good raw materials for making compost.
2. How much compost you need to add per square metre of vegetable garden.
3. Whether it should be applied as a surface mulch or added at a deeper level.
As I use the no-dig method, I apply all my compost as a surface mulch.
With my 50sqm of growing space, my requirements are:
a. 5 cubic metres if I wish to apply a uniform 10cm covering to all beds;
b. 2 cubic metres if I wish to apply a uniform 4cm covering to all beds;
c. 55 pails, if I wish to apply 1 pail per square yard as was suggested in a 1940s publication of a prize winning gardener (of course, it might be helpful to define the volume of a pail, as no doubt different suppliers sell them in different sizes).
On a more pragmatic level, there is the issue of how much compost you can actually generate, rather than how much you would like to apply.
I have two ancient wire cages, which can realistically each be filled to contain about 0.5 cubic metres.
I also have four 0.22 cubic metre ‘daleks’, which can be used to finish compost in an environment protected from rain.
Given the fact that waste materials reduce in volume considerably, you need considerably more starting material than your final target volume of compost.
My approach is as follows:
1. I build a dedicated horse manure pile aimed at producing 0.2-0.4 cubic metres of compost to be applied in late November to the bed growing potatoes the following year.
2. I fill two wire cages in late March/early April when the first cut of grass produces a lot of green waste. I secure cardboard waste from garden centres and straw-based manure to act as brown waste. There is usually also some residue from previous piles which can act as a filler. I apply a few handfuls of volcanic rock dust as I build the layers.
These piles are usually ready to be combined at the summer solstice, at which point they are used as additives to the daleks each time sufficient kitchen waste is present in those bins. During April, May and June, grass cuttings can be left to dry to become brown waste to add to daleks along with comfrey leaves, which accelerate composting beautifully.
As a result, careful management of the bins allows two rounds of composting a year in each dalek, which means around 1 cubic metre of high quality compost is generated from the daleks. I use this to treat the other 3 beds used in the four year rotation, although reality means that it is not all applied in November, rather when it becomes available/when new crops are being transplanted.
A third pile is built in a wire cage around the solstice and a fourth around the end of September. These also serve as ‘fuel’ for the daleks as well as lower grade compost for some of the boundary beds which are cultivated less intensively.
As I grow tomatoes in pots, I also end up with around 0.5 cubic metres of spent tomato compost, which is used where appropriate as compost.
In a perfect world, I would apply 5-7cm of compost uniformly across all beds. In the real world, I apply 4-5cm to my best growing areas and whatever else remains to the rest.
One thing is certain, if you compost all your garden materials rather than giving it each week to the council, you will be surprised how much compost you make yourself.