If you've been thinking about upgrading your composting setup, summer is the time to do it. Not because of marketing. Because of biology.
Hot composting is faster than a normal cold heap, and it handles a lot more. In summer the things that make it work are all on your side. Warmth. Plenty of green waste. A steady flow of material to feed it.
Here's what hot composting actually is, why it works, and what you need to get going.
What is hot composting, and why does it matter?
Most garden bins are cold composters. You add your peelings and grass clippings, and over 12 to 18 months it all slowly rots down into something usable. It works. But it's slow, it can't handle cooked food or meat, and in winter it often just stops.
Hot composting is a different thing altogether. Get the conditions right, a good balance of carbon and nitrogen, enough moisture and plenty of air, and you wake up the heat-loving bacteria. As they break down your waste, they actually warm the heap up. A well-run hot bin sits at 40 to 60°C inside.
At that heat everything changes. You get usable compost in 30 to 90 days instead of a year. Weed seeds and pathogens are killed off. And once the bin is above 40°C you can start adding cooked food, meat, fish and small bones. The sort of stuff that causes real problems in a cold heap. To put the speed in context, a well-run HOTBIN can break waste down up to 32 times faster than a cold heap.
Why summer works in your favour
Hot composting needs regular feeding with a good mix of greens and browns. Summer gives you both.
Greens (nitrogen-rich): grass clippings, vegetable peelings, fruit scraps, coffee grounds, fresh plant trimmings. In summer you're mowing most weeks and the kitchen waste keeps coming. Greens are the engine of the heap. They feed the bacteria and get the heat going.
Browns (carbon-rich): shredded cardboard, paper, dry leaves, woodchip, straw. Browns are the fuel, and just as importantly they hold the structure that lets air move through. Skip them and wet green waste compacts down, the air runs out, and the whole thing goes cold and smelly.
Summer also gives you warmth to start with. An insulated bin makes its own heat whatever the weather, but it's always quicker to get going when it's warm outside.
.jpeg)
The four things your hot compost actually needs
1. Carbon (browns). Cardboard, shredded paper, dry leaves, woodchip. This is the fuel, and the structure that lets air move through. A good rule of thumb is roughly half a caddy of shredded paper, plus a handful of woodchip for every five handfuls of kitchen waste.
2. Nitrogen (greens). Food waste, grass clippings, peelings, coffee grounds. This gets things going quickly. Too little and the bin won't heat up. Too much and it turns ammonia-smelling and airless.
3. Oxygen. Hot composting needs air. The bacteria doing the work can't survive without it. In an insulated bin you keep the air moving by adding woodchip, which props open little gaps right through the material. Never pack it down tight, and never swap in sawdust.
4. Moisture. The contents should feel like a wrung-out sponge. Damp, not dripping. Most of the time the moisture in your food waste and grass is enough on its own.
What equipment do you need?
You can hot compost in an open heap, but without insulation you need a lot of volume to hold the heat. At least a cubic metre. And you have to turn it regularly so the outside works its way into the hot middle. It's hard work and it takes up space.
This is exactly the problem an insulated bin solves. A HOTBIN, Aerobin or Green Johanna holds the heat in a fraction of that volume because the insulated walls do the job for you. You can hot compost in a small garden, on a patio, or tucked in a corner. No big heap, no turning, and it keeps going through winter. (The Green Johanna does its best work with the insulating Winter Jacket on in the colder months.) The cubic metre rule just doesn't apply once the bin is insulated.
For most people starting out, I'd point you at the HOTBIN range. The 100L Mini suits a one or two person household. The 200L MK2 is the popular choice for a typical family. The Mega 450L and 700L are for bigger gardens, allotments or community use.
Each model needs a minimum amount of waste each week to stay hot. Around 2.5kg for the Mini, 5kg for the 200L, 20kg for the Mega. Drop below that regularly and you'll get slower, cooler composting. Still useful, just not the 30 to 90 day turnaround.
A good place to start
If you're new to this, don't overthink it. Start with a base layer of easy stuff. Vegetable peelings, fruit scraps, fresh grass, mixed with shredded paper and a handful of woodchip. Feed it every couple of days rather than in one big weekly dump. Keep the lid shut. Check the temperature after a week.
Once it's running above 40°C you can start adding the trickier things. Summer really is the ideal time to begin. The waste is there, the warmth helps, and by autumn you'll have a bin running nicely and compost ready for the garden.
Shop the hot composters
Further reading
Adam
I'm Adam, the founder of Compost Guy. I'm passionate about empowering people to embrace composting! Whether you're a seasoned composter or just starting your journey, I'm here to help.
