Have you struggled to get your compost heap hot before?
Chances are you have missed one of the five keys to successful hot composting.
Or quite possibly you’ve become disheartened after listening to instructions to turn your heap every other day, or build a huge pile.
(As Joseph Jenkins noted in The Humanure Handbook, the instruction to turn compost heaps regularly has led to the death of some composting initiatives.)
In fact, it’s actually not that difficult, as long as you make sure you follow these five rules.
Do note we won’t explore each rule in depth in this article, but will instead link to guides for each one.
Why choose hot composting?
First, I think it’s worth noting that you don’t need to get your compost heap hot to get compost.
Leave your pile long enough and it will almost certainly turn into compost.
(The exception might be a very dry compost bin.)
However, hot composting does have advantages.
It can kill weeds seeds, reduce the number of pathogens and break down organic material much faster than cold composting.
For more information see Hot v. Cold Composting.
Rule One: Aerate
Bacteria, or at least the aerobic bacteria that get compost hot, need air. (Or, more precisely, they need the oxygen in the air.)
That’s one reason why many hot composting methods place high demands on turning the compost.
However, it’s important to remember that there are many ways to aerate your compost.
You can choose anything from turning the compost pile to including bulking materials to inserting drain pipes.
To help you choose which one is right for you, we’ve put together a list of 11 ways to aerate your compost.
Rule Two: Insulate
In a compost heap or bin, bacteria that work at lower temperatures start to release enzymes that break down organic matter.
As they become more active, they release heat. This encourages heat-loving bacteria which release more heat in turn. These bacteria break down the compost material faster.
Some guides will tell you need a large compost pile for hot composting
But the reason for building a large pile is so that the outer layer provides insulation for the inner layer.
When you turn the compost, you have to put the outer layer on the inside, and the inside layer on the outside, as decomposition will have taken place faster on the inside.
That’s a perfectly viable method, and one I use myself. But it’s important to remember it’s only one way to insulate your compost.
Other ways include using a layer of straw and a compost jacket (an insulating jacket that slips over a compost bin).
See our guide on 17 Ways to Insulate the Compost Pile for more ideas.
Rule Three: Mix ‘Green’ and ‘Brown’ materials
Compost bacteria need both high nitrogen (called Greens) and high carbon (Browns) materials.
(Do note that not all Greens are green in color, and vice versa. For example, manure is brown in colour, but is high in nitrogen, so is considered a ‘Green’.)
Carbon provides energy to the microorganisms responsible for breaking down organic matter.
Nitrogen is required for the growth and reproduction of these microorganisms, as well as for making the enzymes that break down organic materials.
The ideal Carbon: Nitrogen ratio is approximately 25:1 – 30:1 (not every source agrees), but research has shown you can successfully compost with a wide range of materials.
Generally speaking, if you use roughly one half brown to one half green materials you will achieve hot composting.
See The Carbon: Nitrogen Ratio for more details.
Rule Four: Maintain moisture
To successfully compost, you need moisture in your compost pile.
Ideally, you want about 45% to 60% moisture. To assess this, just grab a handful of compost and squeeze it. The compost should feel like a wrung out sponge.
This is one of the harder parts to get right, as moisture can leave the compost pile and be used up by compost microorganisms.
It’s one reason why I turn the compost pile at least once, as it allows me to check how dry the compost is inside.
For more information see our guide to Moisture in Compost.
Rule Five: Limit the size of compost materials
Finally, you want to limit the size of organic materials you put into your compost heap.
That’s because bacteria need to be able to access the material. Larger pieces mean there is less surface area for the bacteria to access.
About an inch to an inch and a half is fine.
Not everything has to be perfectly sized – I frequently put larger things into my pallet bin, and get hot compost.
However, some of it needs to be small, and you do need to have the other elements right.
(I think one reason I get away with larger pieces is I have plenty of grass and sawdust in my current piles, which have a small surface area.)
You can also help the bacteria by slicing open items such as cabbage and purple broccoli stems.
This enables them to get past the woody stem and start attacking the carbohydrates and sugar inside.
To sum it all up, here’s a handy infographic to help you visualise what you need to do. (Click on the image for a larger version!)
Anyone can hot compost
Don’t be fooled into thinking hot composting is difficult.
Some things can make it challenging at times (like a cold winter!)
But if you follow the tips here, as well as in the linked guides, you should have steaming hot compost in no time.