Hot Composting Guide

thermometer showing temperature inside hot compost bin

Introduction

Some of my uses for hot compost include:

Using as soil conditioner, by which I mean mixing it with old compost from pots, or soil in my beds, to replenish nutrients
Providing a rich mulch for fruit bushes, applied in the spring to slowly release nutrients through the growing season
Adding to the planting hole of crops that love a rich soil, like courgettes and other squashes

The video on this page describes my hot composting method to make compost for my garden and allotment. It includes my recipe for making home compost, and at the end of the video, five tips to make hot composting work.

Alternatively, scroll down the page to read the video transcript.

Step By Step Video

YouTube Video

Video Transcript

This video is about hot composting and how I use this method to make compost for my garden and allotment. It includes my recipe for making home compost, and at the end of the video, five tips to make hot composting work.

The biggest advantage of hot composting is how quickly it makes compost compared to a normal compost pile, and how easy it is do. My hot compost can be ready in 4 to 6 weeks, giving me a plentiful supply of compost to use around my garden and allotment. Some of my uses for hot compost include: using as soil conditioner, by which I mean mixing it with old compost from pots, or soil in my beds, to replenish nutrients; providing a rich mulch for fruit bushes, applied in the spring to slowly release nutrients through the growing season; and adding to the planting hole of crops that love a rich soil, like courgettes and other squashes.

To give an idea of speed, my cold compost bins made compost in a year to 18 months. Making hot compost takes 4-6 weeks. This is a huge difference, and transforms the amount of compost produced. Making hot compost has significantly reduced the amount of compost and well rotted manure I buy. I can rely on my hot compost bin to supply compost. In addition, because the speed of composting is faster, my hot compost bin processes much more waste. It eats, for want of a better word, all the food caddies and grass cuttings my house generates. Since starting to hot compost, my bin has eaten everything. Nothing has needed to go out for bin collection day.

In this video I will show step by step how to make hot compost, but I think it is helpful to begin with explaining why I wanted to find a new way to make compost at home.

Why Try Hot Composting?

To be honest, despite knowing all the good reasons for making homemade compost, I had given up with making compost the traditional way using normal compost bins at home. I had realised that I simply didn’t enjoy using my cold compost bins. Whilst they were good as a dumping area for my grass cuttings and food caddy contents, my bins became full whilst I waited for the compost to mature, leaving me with nowhere to put my garden waste.

I had come to hate the job of emptying the bins to turn the contents over so they composted fully, which was hard and dirty work when lifting the compost, and whilst the bins did give good compost, after using it all up, I needed to wait over year, or one full growing season, until I had some more. Ideally I would have had three, or even four bins to make this effective, but I did not want to lose this much space in my garden.

Also, my homemade compost was full of seed that had survived the composting process, which when I used the compost would germinate and give me a weeding job in my beds and pots. The compost was full of worms, which is a very good thing, both for making compost and when added to the soil. However, when I used the compost in my beds and pots, birds would come looking for the worms, and in their hunt for the worms, would lift up my freshly planted seed and seedlings, thereby undoing much of my work.

So, I ended up recycling all my garden waste through the weekly waste collection, and buying shop bought compost instead. I have put my compost bins to good use at the allotment to provide dry shelter to my garden nets, effectively using them as storage bins.

By comparison, I find making hot compost fun. It feels more like watching a magical scientific experiment. I like the way I can see the temperature inside the compost bin, and opening the top of the compost bin is similar to opening the door of an oven, admittedly at a lower temperature, with a rush of hot air coming out. I instinctively step back as I do this. The air is not particularly smelly, a bit like cooked cabbage, but neither it is an aftershave that I want to carry around with me.

How Hot Composting Works

Hot composting is an aerobic composting technique, which is actually the same process that works in a cold compost bin. The compost is made by natural micro organisms in the garden waste breaking down the organic material, releasing heat, water, and carbon dioxide. It is a natural process.

The difference between hot and cold composting is that the heat produced in this process is trapped inside the hot compost bin. The heat accelerates the composting process, it helps the micro organisms break down the organic matter faster, and that is why the compost is ready much earlier than in cold composting.

So, hot composting is essentially the same process as cold composting, but happens faster because the heat is trapped. But in my experience speed is not the only advantage. What I really like about hot composting is that the heat kills any perennial weed roots, and all seeds, during the process. This means that the compost is weed free when I come to use it.

Also, the temperature reached in hot composting should kill any soil borne diseases, helping to keep plants healthy, and reducing the risk of spreading disease around a garden or allotment - that can occur when using compost made in a cold compost heap.

To make hot compost, two essential elements are required. The compost bin must allow air to flow through the compost. If there is not good air flow, instead of aerobic composting, the organic matter may breakdown anaerobically, which produces smelly methane gas and is bad for the environment. The second essential element is that the compost bin retains heat.

To keep things simple, I decided to buy a hot compost bin, but if in the future I decide to make a DIY hot compost bin I will link to it here. The one I bought was made by HotBin, and to be clear, this video is not sponsored or endorsed by HotBin in any way. I am simply sharing my experience of using their product for hot composting.

What I like about hot composting is that the technique is essentially the same as what I used to do to make compost, but it just works better. There are ideal proportions of the percentage, or ratio, of different types of material to add to compost, and whilst I follow these principles, I find there is no need to measure what I add in an attempt to create the perfect compost. If my compost is slightly wet or sticky, it’s no problem. Invariably, my homegrown compost gets mixed with either soil or old compost, and what I make is perfect for this.

My Hot Compost Recipe

My hot compost recipe is as follows, I use three main ingredients. Firstly, the contents of my kitchen caddy. This contains all my peelings, and hot food waste, with the exception of meat and fish. I don’t like to add meat and fish in case it smells, and attracts rodents and other animals to the garden. Unlike cold composting, I no longer worry about composting potato peelings, and seeds from vegetables like butternut squash and tomatoes. The heat will kill everything.

The second ingredient is grass cuttings. I have about 50 square metres of grass at home and mow the lawn regularly. So far, my 200 litre compost bin has eaten all the grass cuttings I produce. Perhaps in a really wet summer, if my grass grew more quickly than normal, my bin may not be able to cope, but so far this has not been a problem.

Both grass cuttings and food caddies are wet content. Whilst great for the compost, if this is all that went into my compost bin, my compost would be a sticky mass. It would risk the air not being able to flow through the bin, potentially leading to smelly anaerobic composting.

Therefore, my third ingredient is to try and balance my wet content with some dry content, roughly in equal amounts, but I don’t measure this.

Over the years, finding enough dry content is what I have found hardest to keep up with. Full food caddies and grass cuttings always kept on coming, but finding more dry content was extra work.

My solution has been to find a source of horse bedding, which is a mixture of straw and horse poo. The straw is dry, helps stop the compost sticking together, and provides air gaps, whilst the horse poo is full of bacteria and nutrients. Well rotted horse bedding is commonly used on allotments as source of compost or mulch. For hygiene, when composting, I always wear gloves.

An alternative supply to horse bedding would be to visit a pet shop to obtain straw, which is commonly used as bedding for rabbits. Depending on what online shopping I’ve done, I also shred untreated brown cardboard, removing any tape and staples before putting it through the shredder.

In addition, the manufacturer of my compost bin recommends adding bulking agent like wood chip. The purpose of this is to keep air gaps in the compost. I don’t have a wood shredder at home, and I don’t want the additional expense of buying wood chip, and so far I have left this out. My compost bin seems to work perfectly without this, but I do use a good amount of straw.

Five Tips For Making Hot Compost

My five tips for making compost are as follows:

Tip 1 - Add A Mixture Of Ingredients Together

I don’t add a lot of one type of compost ingredient at a time. I don’t worry about food caddies, I simply tip my kitchen caddy in when it’s full. However, I never add grass cuttings without straw or shredded cardboard, and I never add straw without grass cuttings.

Tip 2 - Prepare Dry (or Brown) Content In Advance

I prepare dry material in advance, and keep this in bags next to my compost bin so it is ready when needed. To do this, I have a collection of old compost bags from garden centres, but thick black bags would work just as well, and I fill these with dry waste and leave them next to the compost bin. When I cut the grass and have grass cuttings to add to the bin, I am able to add both straw and grass cuttings at the same time, providing the right balance of wet and dry waste.

Tip 3 - Mix Fresh New Content Into Existing Content

I always give the ingredients a good mix when I add them to the bin. I have found that there is no need to reach down to the bottom of the bin each time. What I try to do is incorporate some of the old top layer, say six inches deep, into the content I have freshly added, and mix these together evenly. This seems to accelerate the compost process for the freshly added ingredients.

Tip 4 - Monitor The Temperature And Take Action If Required

I regularly monitor the temperature of the compost bin to ensure it stays around or above the 60 °C mark. What I have found using my recipe, is that there are two reasons for the temperature falling. The first is not enough fresh content, which can happen if I have not added material to the bin for several days. The solution is more fresh content. The second reason is when I have added fresh content, but the temperature does not increase. Using my ingredients, the common reason for the temperature not increasing is that the material is too dry. Therefore, I add more food caddy waste or grass cuttings.

Tip 5 - Remove Content Regularly

I remove content from the bottom of the bin at least once every six weeks. I do this because I want as much homegrown compost as possible, and removing the compost at the bottom of the bin creates more room for the compost at the top. I store the ready to use compost in old compost bags or black bin bags, so I have a convenient supply to hand when I want to use it. An old cold compost bin would be an excellent alternative. In the future, my plan is to fill these up on my allotment, so I have a large supply of ready to use compost there, as well as in my garden.

There is one final feature that I have not mentioned that I like on my compost bin. When hot compost is made, it will naturally release water which will be full of nutrients. My compost bin collects this water, and it is possible to drain this out of the compost bin to use as plant food, diluted in water in the usual way (for example an egg cup worth in a 5 litre watering can). I choose not to use this directly on plants that I eat the leaves of, for example avoiding chard or lettuce, as I don’t know how strong it is or exactly what is in it, but I do use this for flowers in hanging baskets, roses, and all non-edible plants.