Today I spent the morning out on a fieldtrip for my Organic Horticulture course. We had to prepare a large layered compost pile using a wide variety of materials. The end result was a pile about 1.5m x 1.5m and 1.5m high. It was an interesting process, and I have taken away a few things that I wasn't aware of before.
Did you know the optimum ratio for carbon:nitrogen materials is 25:1?
Most people add too much nitrogen material - I know I do anyway.
Nitrogen materials (green) include: green garden waste, weeds, kitchen vege and fruit scraps, grass clippings etc. These provide protein for the microbes.
Carbon materials (brown) include: straw, hay, sawdust, woodchips, dried leaves, twigs, shredded newspaper etc. These provide energy for the microbes.
So although the ratio is 25:1, that doesn't actually mean for example 25 centimetres to 1 centimetre, but it is important to add reasonably equally weighted layers of each as you build your compost pile. As the decomposition process occurs it will reduce to 10:1.
Most compost piles will reduce and do it's thing regardless of how you do it - but if you have a pile too high in carbon, it won't be decompose very quickly as the micro-organisms require adequate nitrogen for the process to work efficiently. If the pile is too high in nitrogen, it will work well, but there is a wastage of nitrogen that is released (as ammonia) into the air and waterways producing pollution.
When you have a higher ratio of carbon (as recommended) you will likely need to start adding water to the heap - I've never really needed to add water because my nitrogen materials have had plenty of moisture in them, however, by adding more brown waste (carbon) I will certainly need to begin to do this. (Unfortunately, today when the water was being added via a large hose from the bore someone turned the tap on too much (when they were trying to turn it off) and it leapt out of the person who was holding it's hands and dowsed three of us head to toe! Luckily I had a spare top in the car and just had to put up with clammy jeans for the next 1.5hrs and yucky hair that went frizzy as it dried!).
For this aerobic system to work efficiently, it also requires air pockets to break the materials down. This can be achieved by creating a layer at the bottom from small branches (about the width of your little finger), as well as ensuring only thin alternatining layers are added ie a large amount of grass clippings will compress and start to decompose anaerobically.
Other useful additives and activators include: blood and bone meal, seaweed, small amounts of wood ash, rock dust and animal (but not pet) manure.
Happy composting!
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