The dream behind the composting effort is that the veg. peelings and shrub prunings are going to be eaten by micro organisms who after their gluttonous orgy will leave behind a nutrient rich humus I will use to mulch my Albertine rose, that in turn will then cover the fence in a beautiful luxuriant mass of flowers.
OK, so we’d better provide the right environment and food stuffs (think oysters, champagne and mood lighting) to encourage the micro organisms to do their thing quickly and efficiently. If we leave the environmental factors (temperature, water, etc) to one side, and look at the material they will consume it becomes apparent an optimum amount of carbon and nitrogen is needed. Carbon is used for energy, and nitrogen to build cell structure. As these organisms live for only 20 minutes or so a lot of carbon and nitrogen rich vegetable matter needs to be provided to fuel the many generations it will take to turn twigs and egg shells into useable compost.
A balance of both elements within the compost bin needs to be maintained. Too much carbon slows the process down because the organisms don’t have enough nitrogen to complete the process of decomposition, and alternatively if there is a surfeit of nitrogen it will escape the bin as a gas, nitrous oxide, a foul smelling waste of the very nutrient you are trying to capture for your plants. People who study these things say a ratio of about 30 parts carbon to 1 of nitrogen is the right mix to enable efficient decomposition. This ratio is generally written as 30:1.
Having learnt that lets look at what we are putting in the compost bin to see if it fits that ratio.
Composting people divide the waste put in compost bins into ‘green’ and ‘brown’ material. Green has more nitrogen in it than brown material. For example, kitchen waste with a ratio of 25:1 has more nitrogen in it than shredded newspaper at 175:1. As it’s usually the green kind of waste that gets added to compost bins some brown stuff needs to be included to up the carbon content. Adding newspaper or cardboard has an added benefit in that green material tends to be fine-textured and moist. If that is all there is in the bin you will end up with a bad smelling sludge, so layering it with dry cardboard opens up the texture (so those micro organisms can breathe) and dries the mixture a little.
The advice scientists and Mr McGregors the world over give is each time you put something in the bin use 50% green and 50% brown material, eg, a bucket of weeds and a bucket of dry leaves.
So this is what I am trying to do with my brand new compost.
However, I’ve no idea if I’m doing it right. I’m throwing in pizza boxes and shredded Guardians, but goodness knows if that is the same volume of green stuff. It’s really a matter of ‘does it look like the pictures in the composting books borrowed from the library?’. No actual measuring is involved.
Apparently you can roughly calculate your C:N ratio by adding up the various ratios of the waste you’ve chucked in then dividing by the number of units. For instance if you added equal parts of kitchen waste, grass clippings and leaves you get this neat formula which ends in a good enough ratio of 34:1:
25:1 + 17:1 + 60:1 = 102:3 = 34:1
Now let’s look at an estimation of my mix. ‘Some weeds and a couple of boxes’ give a ratio of 102:1.
20: 1 + 20:1 + 20:1 + 350:1 = 410:4 = 102:1
Hmm.
