I recall during one of my first Thursdays at the Royal Tasmanian Botanical Gardens (RTBG) in the Food Garden, fellow volunteer A explained to me the processes required for hot composting.
I had heard of hot and cold composting but I had never grasped any of the basic requirements. That day under the tutelage of A, while he moved rotting vegetation in various degrees of decomposition from one bin to another in the Food Garden, I learnt that to encourage a hot compost the physical size of the ‘bin’ must be at least a metre square. This is absolutely essential. Only then is there sufficient distance from the centre to the outside to allow the interior not to be cooled by the air. With this size, the temperature at the core can reach 50 – 75 degrees Celsius. That heat kills off any pathogens and unwanted bacteria, and aids in the breakdown of the vegetation.
Within the RTBG Food Garden we have a model three bin setup; freshly picked new material is deposited into one, moderately decomposed is moved into the second and the third contains almost composted material which is allowed to breakdown further until it becomes nutritious compost.
I realised that at home I didn’t have the resources nor space to create an equivalent composting system. Eighteen years ago when I moved into this house, a green plastic lidded compost bin sat idly in the garden. It looks something like this
And it looks exactly like this as it sits near my red plum tree.
Over the years I moved it around ‘out of the way’, occasionally threw grass clippings and other odds and sods of vegetation in but it came to nothing. I hadn’t a clue how to use it to make compost.
Then, towards the end of last year, I spotted a two hour compost making workshop and registered. The processes were presented simply and I understood, for the first time, how a cold composting system will work – I learnt what you add in has to be added in the right way and in specific proportions. Ah knowledge is such a wonderful thing.
I was inspired and came home to tackle adding ingredients to my compost bin with the sure belief I would be able to produce compost to benefit my plants and feed beneficial microbes.
A good cold compost system layers carbon and nitrogen vegetative materials. The carbon comes from materials such as dry leaves, straw, corn stalks, newspaper, shredded cardboard and small twigs and the nitrogen comes from manure, vegetable waste, lawn clippings, and garden debris. Additionally, a compost pile needs water and air.
At the bottom of my compost bin I layered carbon first using newspaper and straw. Onto this I added some nitrogen via coffee grounds, grass clippings, some vegetable kitchen scraps and a few weeds. Then I continued my ‘lasagne’ until the bin was approximately three quarters filled. On each layer I showered some water to ensure all was moist but not dripping wet.
At the workshop I had been told to leave the container without turning the ingredients for about two to three weeks. After a couple of weeks I looked in and saw some of the surface was dry and in other places there were peculiar fungi sprouting. I realised it needed another shower of water. At this stage it became clear to me that the snug lid prevented any air moving in. So I drilled three holes in one side of the container above the contents. Shut the lid and left it for another week or so.
On the next inspection there were long waving fungi and a yellow coating growing over some of the surface. Time to start turning the contents, I decided. Recently I had purchased a special turning tool – which had been shown at the workshop.
This tool was a boon. I spiralled the tool down into the container again and again to mix the contents. At some levels the layers were bone dry. So I showered more water over and closed the lid. Over the next few weeks I twisted and turned the tool to remix the materials, then watered the contents before closing the lid. After two months the volume had dropped by half so I was encouraged that compost was on the way despite the ingredients seeming very much to be as they were before. But obviously decomposition was occurring.
Then I forgot about it believing that I would never achieve compost; believing that I simply didn’t have the right proportions of carbon, nitrogen, air and water. As lovely although perplexing as it was to see unusual and coloured fungi sprouting, I was sure I was not creating compost. I guess I determined to wait until it all settled then I would simply break it up and scatter it over the garden, shrug my shoulders and give up.
So I was extraordinarily surprised when I opened the lid three weeks ago. No fungi. Just a dark damp wonderful pile of compost. Not very high; amazingly diminished from the starting height.
Since then I have distributed the rich compost around my lemon and mandarin trees, watered it, and covered with a mulching straw.
On reflection I suspect my proportions of carbon to nitrogen weren’t the best. Ideally I needed to create a C:N ratio around 25 to 30 parts Carbon to 1 part Nitrogen. Excess Carbon slows decomposition. Excess nitrogen makes a stinky pile. Thankfully mine never smelled bad.
Nevertheless and inspired by that success; the process is clear to me. Layer the ingredients appropriately, keep them moist, turn the contents once a week for weeks after letting it sit for a couple of weeks or so, then forget about it. All in all – allow about three months. Maybe I will get better and more in tune with it and create compost in a shorter period – who knows how soon before I achieve the ideal carbon to nitrogen ratio. For the moment I have achieved a tiny success and I am super excited for the future.
Last week I lasagned a new bin load ready to make compost. The bin includes straw, paper and cardboard plus coffee grounds, seaweed, grass clippings, some weeds, some household vegetable waste and horse manure. Each layer was moistened, and the air holes are clear. In a week or so I will have a peek to see how it looks, and perhaps be ready to start stirring with my wonderful compost tool. I have my fingers crossed that more compost will result.