Everyone seems to have got the idea that we must make compost hotter. Any organic material will rot down into compost. It doesn’t necessarily have to get hot. So, if you are looking at your compost pile and it looks and feels cold, this isn’t a problem. Don’t allow the fact that your compost isn’t getting hotter to affect your day.
Adding carbon will make compost hotter
If you’re convinced that your compost must be hotter than it is, then, you may find that you need to add more carbon based materials to the compost that you have. Carbon is an energy element. It will be in cardboard, paper and generally woody materials. The adding of this to any compost will be the best you can do to make your compost become hotter.
If your compost pile is made up of mainly woody material, it may be that it’s too dry. Dry grass won’t rot. The simple addition of water will change this. You won’t need to add much. Organic materials only need to be moist for the composting process to begin.
You may find that a dormant heap of dry, organic material will become significantly hotter after adding enough water to make it damp.
Some will tell you that you need to build your compost pile with the specific aim of producing heat and that you need to monitor the temperature and somehow control the heat to prevent overheating.
A compost pile made up of the right proportions of ‘greens’, ‘browns’ and sufficient moisture, will become hotter without any intervention from anyone. The compost will do its own thing.
You may be tempted to dig over the heap in an attempt to help the compost become hotter than it is but if there is evidence that heat is being generated, the best thing that you can do is to leave it alone.
Don’t dig compost in the hot phase
Digging over a compost heap while it’s going through the hot phase, will risk cooling of the compost mass. If you see steam rising from your compost, leave it for a couple of weeks, or possibly longer if you have a big compost pile.
A compost pile that’s become hot, will remain hot if the compost mass isn’t disturbed. The fibrous nature of compost can be very insulating which means that the heat that’s generated can’t easily escape. The heat will build up. This is the main reason why a compost pile becomes hotter.
There are suggestions that the heat generated in a compost pile could be collected and used for domestic heating. This could be practical if the compost pile is large enough. A small compost pile may become hot and generated a considerable amount of heat. It may be quite noticeable if clouds of steam are being generated, especially if it’s a heap of lawn clippings.
If you have ambitions of extracting heat from a compost pile, you need to be aware that the heat from a compost pile will only last for a short while. The structures required to collect the heat will only be in use for a short while.
You may want to make compost that becomes hotter but high temperatures will inevitably kill some of the microorganisms that are needed for breaking down organic material. Should you worry about this? No. In the right conditions where heat can be generated from compost, the mass will get hotter and hotter until the temperature reaches the maximum potential.
When the energy source within the mass has been exhausted, the mass that’s generated heat will start to cool. The heated heap will continue to make compost. Any microorganisms that will have succumbed as the compost mass became hotter, will re establish a place in the cooling compost, having survived in parts of the compost where it didn’t become hotter to the point where they couldn’t survive.
What is the difference between hot and cold composting?
The only difference between hot and cold composting is the speed. When the conditions are right in a compost heap, pile or bin the temperature goes up and we get hot composting. Any organic material in a hot composting pile will break down much faster.
The speed will only apply in the early stages of the composting process.
The heat will only last for a short while. The length of time that compost will remain hot depends on the size of the heap. It will cool down and revert to a cold rot to continue to the end conclusion.
Both hot and cold composting will deliver usable compost.You will often have little choice over how your composting system works. It will depend on the ingredients and volumes of materials involved.
It’s largely pointless concerning yourself over what the difference is between hot and cold composting. Making compost from organic material will happen one way or another. Hot or cold composting will be irrelevant when you come to dig out the finished product.
You won’t notice any difference in compost that has been generated from either hot or cold composting.
There are plenty of arguments being put forward that insist that you must aim for a hot composting system. The heat generated in hot composting will kill weed seeds but unless you have the compost in a closed vessel that comprehensively heats the entire mass to the required temperature, it won’t get all of them.
The same applies to the claim that hot composting will sanitise the compost that you’re making. If the composting heat can be held at a temperature of 60degs C for long enough, this will kill potentially harmful pathogens. As with the weed seeds, if the entire mass isn’t heated to the required level, then there will be pockets where things can survive.
Hot composting will kill pathogens where the compost is hot enough. Cold composting need not be a problem when considering pathogens. Cold compost is much more attractive to worms. Worms don’t like it hot. Worms will consume pathogens and render them useless. In cold compost, worms will cover every part and digest everything at least once.
The general advice is to dig over a hot compost pile and aim to place the outer cold parts in the middle of the repositioned pile. This is intended to expose the cold regions of a compost pile to the heat that’s generated in the middle of a pile. This may work and the cold parts may become hot enough to sterilize it.
Relying on the heat from hot composting in a domestic setup would be risky. It’s worth noting that when you dig over a hot or heating compost pile, that the digging action will allow heat to escape and the pile, as a whole, will cool down. This would then take the pile from being hot compost to cold compost.
Cold composting provides an opportunity for every seed to survive and germinate. The thing about cold composting is that you can know that this will happen and be ready for it. Very often rogue seeds will germinate in cold compost. Because of the high level of nutrients in compost, hot or cold, these seeds will grow quickly and clearly present themselves.
The plants that grow from these seeds will be tall and vulnerable. They can easily be broken off. In a tumbler composter e.g. the Rolypig compost tumbler, seeds will germinate into small plants that will become broken and crushed when the barrel is rolled over.
The Rolypig is a cold composting system. It’s better if weed seeds do germinate inside a cold-compost tumbler because the rolling action will get rid of them. It’s just another way of ‘sterilizing’ the compost of any rogue seeds.
Some people have doubts about putting plants in with the compost that have been treated with herbicides. The worry appears to be that there may be residues that survive the composting journey. There is data that shows that these residues will break down completely during the composting process. There is a claim that herbicide residues will break down more than 30 times faster during hot composting compared to cold composting.
It needs to be understood that this rate of break-down will only happen when hot composting is actually happening. This period of time may vary according to varying factors that will influence the overall composting process.
The quantities of herbicide that are likely to find their way into compost via treated plants, is likely to be very low and will break down over the prolonged time-span, regardless of whether you insist on hot composting or settle for cold composting.
The initial rate of decomposition will be much higher if hot composting is encouraged to take place.
The heat from hot composting will kill insect larvae and fly-eggs. So there should be a reduction of maggots in the main part of compost where enough heat is generated. There may be some that survive if they can find an area where there is little or no heat.
After the heating phase has passed, there will be little or no food value in the parts of compost that have been heated, to attract egg-laying insects.
The opposite will be happening where there is cold composting. The organic material will rot very slowly in the early stages and throughout the cold composting process. This will provide plenty of opportunities for insects to lay their eggs and maggots to take up residents.
Cold composting doesn’t need to be a problem as regards flies and maggots. The regular adding of hydrated white lime will deter flies and other pests of a rodent nature. The lime will also accelerate the composting process almost to the point where it could compete with hot composting in the early stages.
Then we have the question of smells. Some will say that cold composting will generate more of a smell than hot composting. Both can perform admirably when it comes to smell. Hot composting will always have the edge over cold because water is driven off as vapour.
Water vapour will become airborne and have the potential to reach more noses. This will continue until the heat level drops. After this point the pile will revert to a cold composting mode.
Cold composting will generate some water vapour. In a small, domestic composting system there’s rarely enough of a mass of organic material to generate enough heat to display noticeable quantities of water vapour.
The heat from hot composting is often seen as a convenient way of driving off excess water, thus allowing a more efficient decomposition there after. This is true. A compost pile that’s too wet will be self sealed. Air won’t be able to get in so easily but, unless the composting container is completely sealed, excess water will drain away.
Air will find its way into any composting mass, hot or cold. All organic material will convert into compost. Whether hot or cold there will be no difference in the final outcome, it will all get there in the end. It’s just a matter of which way it will happen.