Anyone who is getting into composting will hear people talk about hot compost and how having a hot compost bin helps to break waste down more quickly and effectively.
Hot compost kills weed seeds and pathogens too, so it’s a great way of ensuring your compost is ready for vegetable patches and your garden.
However, you may find that your compost simply doesn’t seem to get hot enough.
If you’re spending days frowning at the thermometer and then peering at the heap, we’re going to cover “why is my compost not getting hot?” so you know what steps to take to increase your compost’s temperature and efficiency.
As you implement this information, bear in mind that it will not take effect immediately. In fact, it can take up to four weeks for your compost to reach high temperatures, even if it has everything it needs to do so.
In warm weather, it should heat up more quickly (sometimes as fast as a week), but don’t expect immediate results from following these steps; you need to give them time to work.
So, let’s find out why your compost isn’t getting hot yet!
Not Enough Nitrogen
One of the best ways to get your compost to heat up is to add nitrogen, and ensure that you have a high ratio of nitrogen to carbon.
Nitrogen is sometimes referred to as “greens” (and carbon as “browns”), but it isn’t necessarily green in color.
The “green” instead refers to the idea that it is green wood, fresh ingredients, etc. Nitrogen is found in food scraps, grass clippings, etc.
Carbon is found in dry twigs and sticks, eggshells, nutshells, and things like shredded card and paper.
You’ll find many different recommended ratios online, and also many people who pay minimal attention to the ratios and just add what ingredients they have (within reason).
You will soon know if your balance is off, because a heap that is too high in carbon will often dry out and end up inactive, and a heap that is too high in nitrogen may end up slushy and messy, and will smell bad.
Adding lots of greens to your compost is a good way to increase the temperature. You should make sure that there are still enough browns by tearing up card or adding sticks.
These will help to keep the heap oxygenated by adding pockets of air.
Stir the two together to ensure that the browns are integrated with the greens and prevent them from compacting, and you’ll have a hot compost heap in no time.
If you find you have added too much nitrogen, don’t panic; you just need to shred some newspaper or card, or add dried leaves, straw, etc., and it will sort itself out in a few days.
You can’t go too wrong, so experiment, and don’t worry if you find you have to correct it.
Not Enough Turning
Turning your compost is also key to keeping it hot. That might seem odd if you can feel the heat escaping, but it’s actually really important.
By turning the heap, you are doing two things.
Firstly, you’re ensuring that the ingredients are mixed up and carbon and nitrogen are stirred together, not sitting in clumps that will overwhelm anything trying to break them down.
This also helps with compaction issues that make it hard for worms and bacteria to work.
Secondly, you’re introducing lots of oxygen. A lot of the composting work is done by aerobic (oxygen-loving) bacteria. These bacteria need oxygen to survive, and if they run out, they will disappear.
If this happens, you will likely notice an unpleasant scent around your compost heap, because they’ll quickly be replaced by anaerobic bacteria (those that don’t need oxygen), which produce a bad smell.
Fortunately, this is easily rectified – you simply need to turn the heap and the aerobic bacteria will quickly reappear.
So, how does that connect to heat? Well, the more oxygen there is, the more active the aerobic bacteria will be, and they produce heat as they break the food down.
If you keep them happy with lots of oxygen, they will break food down faster (meaning you get compost more quickly) and create more heat.
In very cold weather, you should expect your compost to get a bit cooler and to slow down. There isn’t a lot you can do about this.
While large compost piles may remain quite warm and active even in the winter months, they will still probably slow down.
Remember that everything slows down in winter. Your compost worms may not be as active, and there will be less natural heat to help the decomposition process along.
Indeed, if you have frosts, your food is essentially in a freezer, and we all know that freezing food stops it from decomposing
You can buy compost bin jackets to help keep heat in, or you may want to cover your compost with something like carpet (use natural fibers only to avoid plastic shedding into your soil), but there isn’t a huge amount you can do about cold weather cooling down your compost heap.
Too Wet Or Too Dry
If your compost is too wet or too dry, it will become inactive quite quickly, and this will mean that there is no heat – because you need the bacteria for the heat.
You can easily tell if your compost is not moist enough (or too moist).
Squeezing a handful of compost should be like squeezing a wrung-out sponge. It should not be dripping, but should not feel dry either.
Compost that is too dry won’t provide a good environment for the bacteria, so you need to add some moisture.
You can do this by simply watering your compost heap a bit from time to time, or by including more wet ingredients, such as fruit scraps.
Don’t water the compost too much – remember, you’re aiming for damp sponge, not sopping wet.
If you water it too much, you’ll wash a lot of goodness out into the soil, and will also cause problems with your compost being too wet (which we’ll come to in a moment).
Rain will also help your compost, so if you have a covered bin and it’s getting too dry in there, consider leaving the lid off for a while so it can get wet.
If your compost is too wet, there won’t be enough oxygen for the bacteria, so you’ll again see that it stops working.
It may also start to smell bad, because the ingredients will be rotting and algae may be building up in the water.
Fortunately, this is also easy to fix; you simply need to add some dry material, especially cardboard or newspaper, to soak up the excess moisture.
Cover the heap for a few days (use a tarp if it’s not a lidded bin) if you have heavy rains.
In general, green ingredients add moisture and brown ingredients soak it up, so use this to help correct the moisture balance in the compost heap.
The Wrong Size
A compost heap that is very small will not build up much heat. Compost piles often need to be around 3ft by 3ft as a minimum if you want them to get hot.
You can compost in smaller quantities, but you are unlikely to achieve much heat while doing so.
Again, you need quite a lot of bacteria to make heat, as well as the insulation of the pile. A small compost heap will not have either of these things, and will therefore not get very hot, no matter what you do.
Equally, you do not want a massive compost heap. It might seem this would be an advantage, but the problem with huge compost piles is that they tend to get compacted, and they are hard to turn or stir.
Large compost heaps are unlikely to have enough oxygen to encourage the bacteria needed to break the food down.
If possible, it is better to create several medium compost piles, rather than one big one, so that the weight of the pile doesn’t squash all the material down.
Not Enough Bacteria
Usually, bacteria should form on their own in your compost, but it’s possible that they haven’t done so in yours yet, especially if the pile is new.
Fortunately, you can speed this up by taking some soil from your garden and adding it to the compost heap.
This should have plenty of bacteria, which will quickly multiply and spread through the compost heap, getting it active and – hopefully – hot!
Remember that you won’t see instant results from following these tips, but that these are the points you need to check if you’re struggling with cold and slow or even inactive compost.
You need to ensure that the compost has enough nitrogen and oxygen for the bacteria to operate effectively, and that it is large enough (but not too large) and wet enough.
You also need to check that the bacteria are in there in the first place!
If you do all those things, you should soon have hot compost, decomposing nice and quickly, ready to be used in the garden.