The world-changing potential of hot composting

Photo courtesy of Wikicommons.

As long as there have been humans, we have taken the parts of plants we don’t eat and thrown them back onto the soil again, knowing they would turn back into soil to create more plants. Until historically yesterday.

Now many modern people take their food and seal it away in plastic, so that the only bacteria that can work on them are anoxic bacteria that generate methane – a greenhouse gas about 35 times worse than carbon dioxide. Some of us compost our organic waste – food, paper, lawn clippings --  to let the proper critters munch away and let it alchemically turn into soil again.

Ordinary composting, however, has some disadvantages that every gardener knows well. One can’t simply add bones or meat – and some gardeners even avoid eggshells – for fear of attracting vermin. Also, plants that have gone to seed cannot be added, or the resulting soil will be peppered with the beginning of next year’s weeds. You can’t add diseased plants, or the diseases might remain in the resulting soil, ready to infect next year’s crops. Also, it takes a long time, and one loses much of the kitchen waste volume in the process of rotting down.

Imagine, then, a new kind of composting, one that avoids all these problems at once – no more weed seeds, no more disease, no more vermin. Imagine being able to compost almost everything, and keep the majority of the biomass. Imagine, finally, that it only takes a matter of weeks and not months.

What makes hot composting, or Berkeley composting, work is bacteria; instead of the usual variety of bacteria that breaks down over several months, hot composters find the right balance of materials – more on this in a moment -- to attract aerobic, heat-generating bacteria. The bacteria generate heat just as your body does -- between 55 and 65 degrees Centigrade, hot enough to kill any weed seeds and diseases.

In order for this method to be effective for you, you need the right balance of materials to compost; if the carbon/nitrogen ratio is too high in carbon, the compost will not get hot enough or break down quickly enough, and one must add something like manure or grass clippings. If the mix has too much nitrogen, rather smelly bacteria will take over, and the mix might get slimy.

the ratio one looks for is between 25 and 30 parts carbon-rich waste to one part nitrogen-rich waste, proportioned by weight. Carbon-rich materials are typically dry and brown, like sawdust, cardboard, paper, dried leaves, straw and other, similar things. Nitrogen-rich materials are typically moist and fresh, like kitchen waste, fresh lawn clippings and vegetable scraps. Sometimes carbon-rich materials are called “browns” and nitrogen-rich materials “greens” for simplicity, but these terms can be misleading: coffee grounds and animal manure, whatever their colour, would also be nitrogen-rich.

To get the right C/N ratio, keep in mind that all plants have more carbon than nitrogen, so virtually all materials have a ratio of at least 1/1. Wood chips have a ratio of 400/1, newspaper has 175/1, and straw has 75/1. Vegetable scraps are about 25/1, fresh grass clippings 20/1, and chicken manure  about 12/1. Urine has a ratio of about 1/1, and is excellent to add to soil in whatever way does not violate your social anxieties or local ordinances.

It is a bit awkward to weigh things before adding them and then doing the math, but you quickly get a feel for the practical effects of your most common additions and see how they affect the whole, in the same way that you do with cooking. You can adjust the ratio of certain additions; for example, by letting some of your lawn clippings dry and then raking them up, while mowing another section into a bag and depositing while still green, to get the ratios you want.

To experiment with this yourself, first fill a cubic area about 1.5 metres across each way with kitchen waste. Leave the compost for four days with no turning. Then, turn the compost every second day for the next 14 days to oxygenate it, making sure to turn it thoroughly from the outside in to get everything well mixed. By the 18^th day, it should look like soil – but you still need to let it rest for several more weeks before planting in it.

Not everyone has the amount of organic waste to try this, but you could get your neighbours to participate by getting them to recycle and reducing their trash bill, or doing the same for local shops that have produce they throw away. If you live near a park, you could see if the city wants somewhere to put their lawn clippings.

Composting this way generates heat that some people can use to heat their homes or water supply – I’ve taken a very hot shower outside on a very cold Irish morning, using no electricity or fossil fuels. I just snaked the hose up through the compost, and the heat from the bacteria heated the water by itself.

Households in northerly climates could spend perhaps $2,000 a year on heating. Imagine homes with hot composters attached, which can use their heat -- perhaps in conjunction with an attached greenhouse. Such simple innovations, if handled rightly by the households, would turn their waste into soil quickly at a time when we need more soil to plant in. It would cut their emissions from garbage and at the same time cut their emissions from fossil fuels, since they would not have to burn as much gas or oil. It would reduce their debt, and their dependence on government and corporations, all at the same time. Few simple, at-home innovations could have a wider impact if widely embraced.