In this article, we’re going to look into hot composting vs cold composting (what’s the difference).
It seems that the compost world is vast, and there’s always new things to learn, and knowing where to start can be a major challenge.
If you’ve just come across the terms hot composting and cold composting, you might be wondering what the difference is, and which method tends to be more effective.
Obviously, the differences are going to be mostly down to temperature, but let’s take a closer look at the ins and outs of each.
Many dedicated gardeners will swear by hot composting as a better solution, but you may find it easier to start with a cold compost pile if you’re a beginner.
What Is Hot Composting?
Hot composting is usually considered a compost pile where the temperatures are between 110-160° F.
Temperatures higher than that are going to cause problems for the microorganisms and bacteria living in the compost heap, and temperatures below would no longer be considered hot composting.
You can buy compost bins specifically designed to increase your ability to compost at these temperatures. They tend to be pricey, but many gardeners feel they are worth the investment.
However, you don’t have to have a special bin, it just makes the job a bit easier.
Hot composting will still require you to have a good mix of browns and greens, water, oxygen, and access to the soil.
Hot compost piles need to be quite large, at least 3’ x 3’ x 3’, to trap enough heat to work properly.
A bigger heap will hold more heat. It is best if you can build a hot compost pile “as one,” rather than adding bits later, or you will increase the time before the compost is ready to use.
What Is Cold Composting?
Cold composting is – as the name suggests – when the compost heap is colder.
That doesn’t mean it has to be stone cold; you can even have “warm composting” as a middle ground. It just means that the compost heap won’t actually get very hot inside.
Cold composting often involves less work, as you don’t have to keep checking the temperature pile, and you won’t need any special equipment to do it. You just need a space and some organic waste.
Cold compost heaps don’t really have specific sizes they need to be.
Large will again conserve more heat and stay more balanced even in external temperature and weather fluctuations, but a cold compost heap will still compost even if it’s tiny.
What Are The Advantages Of Hot Composting?
If hot composting is more work, why bother with it? Well, it offers some significant pay-offs for the extra effort.
Firstly, you will get compost faster. This means that you can get through more waste, which is great if you have a large household or a lot of scraps to dispose of.
You won’t end up with an inert and ever-growing pile clogging up your garden and looking a mess.
You also have compost available faster. You can get compost from a hot composter in as little as a month if you are lucky and cut your scraps up small, though 1-3 months is probably a more realistic expectation.
Turning your compost regularly will help to speed it along.
Secondly, your hot compost will keep going year-round, whereas cold compost slows down or stops during the winter. That means hot compost is easier to keep on top of and doesn’t build up.
Hot compost is better at handling a wide range of foods because it reaches higher temperatures.
It will kill off potentially harmful bacteria more effectively, and it’s also a great way to deal with invasive plants.
If you throw weeds and weed seeds onto a cold compost heap, you can actually be making your problem worse, because they can survive and may sprout from the compost when you use it – with a nice dollop of your rich, carefully-nurtured new compost to help them on their way.
Hot composters reach temperatures that are capable of killing weed scraps and seeds, which is a much better solution than having to put them in a landfill.
What Are The Advantages Of Cold Composting?
Cold composting is less work, to be blunt. You don’t need to be paying attention to the heap all the time, or checking its temperature on a regular basis. You can leave it unattended without any major issues.
However, cold compost does have the disadvantage of slower processing, and it can take 12-18 months to get usable compost from a cold composting pile.
A nice in-between is warm composting, which may actually occur even if you aren’t particularly trying to heat your cold compost pile up.
The activity of the microbes can boost temperatures to surprising levels, especially if you turn the heap often enough.
A bigger compost pile is more likely to result in warm composting, as is adding slightly more nitrogen-rich ingredients (e.g. cut grass).
What Ratios Should I Use For Each?
You may be familiar with the idea of composting ratios, and the “browns” and “greens” you can add. More greens will result in a wetter mix, while more browns will cause your compost to dry out.
Keeping a balance is important, but how does this differ between hot and cold composting?
Hot composting will thrive on high-carbon materials. This could be twigs, stems, corn cobs, rooty plants, little bits of wood, even thin branches.
About two-thirds of your hot compost should be made up of these things, with one third being nitrogen. Nitrogen is usually kitchen scraps, vegetables, weeds, etc.
You should also add some potting soil, introducing microbes and bacteria to start the process. These things will find their way in independently if you don’t, but adding some will speed things along.
Cold composting also needs to be balanced, but the ratios matter less. Because you are able to keep adding to a cold compost heap, you can adjust it according to how it looks and behaves.
Add more brown material to a compost heap that’s looking wet, and more nitrogen and liquids if the heap is drying out.
What Else Should I Know?
Both kinds of compost are essentially doing the same job, just at different rates and with slightly different pros and cons. You can easily try both and settle on which suits you in the long-term.
You can speed both kinds of compost up if you turn them frequently, because introducing air into the mix helps the bacteria to function.
It might seem that you’re letting valuable heat escape, but actually, this will help both kinds of heap to reach good temperatures.
Turning your pile also ensures you don’t get “pockets” of a material that isn’t breaking down because it has become too compressed, and it reduces the appeal of your compost heap as a home for rats or other invaders.
If you’re depending on your hot composter to kill off harmful bacteria and weed seeds, make sure it is actually reaching the temperatures it should be – especially if you intend to use the compost for food crops.
You shouldn’t just assume it will get hot enough, so get a thermometer and check regularly.
If you’re short of space, hot composting is a better option because it will keep your bin(s) turning over faster, and will mean you can process more materials more quickly.
It also means you can compost slightly more variety, as it is capable of handling more foods.
Hot heaps also tend to smell less, so if that matters to you, take it into consideration.
While a healthy cold heap should not smell bad, it is easier for them to get water-logged.
This drives out the oxygen, and then the heap tends to become anaerobic, which does not smell good at all.
You can fix this by adding more browns or creating drainage for your cold heap, but it is still worth considering which is more suitable, especially if you have a small garden and you don’t want to be treated to “compost odors” at times.
Cold compost heaps are also more prone to fly breeding, although if you have a lidded compost bin, this may be less of an issue.
Hot compost usually gets hot enough to kill flies and their eggs, so they won’t be using it as a breeding ground and then swarming around your garden in the summer.
The long and short explanation is that if you’re prepared to put in (quite a bit) more work, hot composting offers you a safer, more efficient, and generally better experience for lots of reasons.
However, if you just want your compost to get on with composting without much maintenance, cold composting is better.
You won’t have to spend time working out ratios, and you can just add to the heap as and when, rather than trying to build a complete pile in one go, which may not be practical for you.
You can find a happy medium between the two with warm composting, but don’t rely on this method to kill off pathogens or weed seeds; it will probably not get hot enough, even in summer, and adding too much nitrogen to try and boost the heat will cause you other issues.