Compost is an essential part of any garden. It is an efficient tool how to return excesses back into the system, using processes which have the ability to break down a mix of different types of matter into an on nutrition rich humus. Compost helps to maintain the garden healthy and sound. But what if your cold compost heap doesn’t provide enough of substrate? Before you leave for the nearest home & garden supplier, try the hot variation.
Almost everything can be used again
“Catch and store energy,” is a second permaculture principal by David Holmgren. Essentially, this principal invites us to reuse the energy which has not been used by the system (your garden). There is a broad scope of human activities where this principle can be applied. Composting is one of the fundamental methods allowing us to make garden waste to work for you, not against you or the Earth.
This text was originally published in our Czech mutation in April, a time of a year when growers have already been super busy for solid few weeks. In the temperate zone, April is a month when most of the crop is planted.
But before then, after a long, cold winter, the first thing which comes to your mind is that you want to perform a proper spring-cleaning. After you gather all the debris and stuff, then you decide what to get rid of, what’s worth of keeping or burning in a fireplace.
It is estimated that up to 90% of the pile you rake up, such as leafs from last autumn, grafted branches, dry grass, windthrows, various types of wood, cardboard boxes, and items that somehow have appeared over the past year in your garden, can be reused as an additional source of energy. Reusing energy should always be preferred.
Once you’ve gathered all the unwanted, redundant stuff, take the effort and divide the pile into two parts – organic matter and other. It is important to realise that the organic bit, including secondary industry products, is everything that comes from the Earth (any kind of crop production including forestry or livestock production). Therefore, even the old, broken broomstick you are about to burn is your thing.
The other remains usually are plastic (boxes, pots, broken garden tools, handles, cable ties, packaging, containers and more), metals (old nails, connecting material, tins etc.), glass, and various chemicals. Again, most of them can be scrapped or recycled. One way or the other, it is always good to bear in mind that the best waste is the one we don’t create.
Healthy compost, healthy garden
In comparison with the cold method, fast composting requires external energy input – human work. Whereas, for the cold method, time is the primary factor. Geoff Lawton, an expert with an international reputation in permaculture, is a big fan of hot composting. Be worth mentioning the documentary, Permaculture Soils (2010), where he widely talks about the Berkeley method and also expands the concept. However, it was prof. Robert D. Raab from the University of California, Berkeley, who researched and introduced this method as first.
The key to success – good preparation of raw material
How to go about it and achieve success? Before you start mixing the heap, everything, you decided to use, needs to be chopped, crushed or split into smaller fragments. Just parts which are not bigger than one inch (1.25 – 2.5 cm) are compostable. “The harder or the more woody the tissues, the smaller they need to be divided to decompose rapidly. Woody material should be put through a grinder, but most grinders chop herbaceous materials too finely for good composting,” it says in prof. Raab’s paper.
It is essential to find a place with well-compacted dirt on the ground of a minimum surface of 5m2. It is because you will need to toss the heap from one side to other. It is crucial that there will not be air flow blocked from the bottom due to aerobic processes, which occur during the breakdown.
Carbon versus nitrogen
Carbon to nitrogen ratio should remain 30 to 1. Raab suggests, based on experience, that “this cannot be measured easily, but mixing equal volumes of green plant material with equal volumes naturally dry plant material will give approximately a 30/1 carbon to nitrogen (C/N) ratio.”
Bear in mind that nitrogen (material high on nitrogen) is the fuel of the process. If you add too much of N into the mix, it will result in too rapid composting, which will cause the loss of volume and occurrence of lousy smell (due to the release of methane).
Nitrogen high material is fresh cut lawn, weed, cut-offs from fruit and veg, green waste from the kitchen. Another source and also an initiator is manure. As for adding different types of manure into the compost, Lawton and Rabb part their ways here.
Lawton recommends to throw in manure produced by herbivores. He says that we also should not be worried about adding poultry, pig, or even human manure. A mix of manures should be used moderately as it works only as a bacterial starter. It is essential to stick to the C/N ratio at all times (see table). He suggests that if you use a mix of several types of manure in order to obtain the most varied combination of mineral compounds. This is essential for plants’ good health.
Whereas, Raab, in his paper, strictly doesn’t recommend to use manure produced by omnivores (including human manure). The reason is that such manures can contain active pathogens, which could possibly infect humans. It is, therefore, necessary to find out more about this issue and decide for yourself. Lawton argues that the heat, which occurs during the decomposing, will kill all such potential pestilential. Still, it is highly recommended to be sure that you know what you are doing here.
The source of carbon is actually any dry, organic debris and matter (including those from you spring-cleaning). If there is needed more to reach the minimum (or wanted) volume, you can add more in form of hay, straw, or mulch. Both men recommend using old newspapers, cardboard, paper bags, boxes and the like. Remember that they all have to be well chopped and mixed.
High or low humidity is in both cases bad, which can lead to failure of initiating the composting process. Therefore, the ideal humidity is about 50%. This is fairly hard to measure. According to Lawton, a practical test can be applied. Dig out an ideal sample from the heap (big enough to fill your hands) and squeeze it with full force (don’t wring it). If it’s done correctly, water should just drip from the sample.
This is the most crucial factor. As mentioned above, during the breakdown heat is released. It is the result of the activity of microorganisms. To be able to reach and maintain the right temperature, the volume of the heap must be at least one cubic meter. If it’s more than that, but the ratio of C/N is met, it doesn’t matter.
Both men part their ways again here. Nevertheless, they agree on the temperature scale, which is 55 °C – 70 °C. Whereas Lawton strictly prefers to maintain the temperature between 55 °C and 65 °C, Raab assures that it can climb up to 70 °C. However, it cannot exceed it. If it does, all the good microorganisms will be annihilated, and this means the end of all effort. Game over!
How to measure the temperature if you don’t earn an industrial probe thermometer? You can do a practical test using your hand. Essentially, you have to dip it in the heap and use common sense during judgment: If the heap is about 60 °C hot (happy medium), you’ll feel the heat as quite uncomfortable. Any temperature close to 70 °C is just too hot, and you’ll flinch from it. As this is a relatively hostile environment for a human body, you would risk scalding at such high temperatures. It is our reflex. Maintaining temperature is a must. Therefore, you have to protect the heap from rain which could cool down the heap. Throw a tarp or a plastic sheet over the top and cover it well if you have to.
To avoid overheating, you have to regularly turn the heap over in the following 18 days. The first turn comes on day four. It is the day when the compost should reach the maximum temperature. Then, you have to turn it every second day until day 18. The hot inner layer must come out. Keep turning the hep according to the timetable until the temperature significantly drops. The mix should be ready by day 21 at the latest.
No pain no gain
Compared to the classic cold composting, Berkeley method provides you with compost mix in relatively short time without losing volume. However, as you suspect well, it is not for nothing. This method demands adequately enough human work (energy input). I would not find it a disadvantage as such hard work can easily substitute your work-out day. Therefore, you can be spared a wasted afternoon in traffic on the way to your favourite gym.
A big advantage of this method is that you can breakdown almost everything that is compostable, even lightly toxic items. So don’t hesitate to chop up and throw in the old wooden, some time ago varnished broomstick. Have fun!