Two drums sit behind my shed. One is a 200-litre two-chamber tumbler I bought in 2014. The other is a 90-litre single barrel, picked up second-hand for twenty pounds. Between them they have taught me more about composting than any book, mostly by failing in interesting ways.
Tumblers sell on a promise. Load the drum and collect compost in a fortnight. The reality is narrower than that. It is also more useful.
What follows is what a tumbler genuinely does, where it falls short, and the numbers I actually use after eleven years of running one.
What a tumbler really changes
A tumbler does two jobs. It turns the pile for you, and it keeps the pile enclosed.
Turning matters because composting is aerobic. The microorganisms doing the work need oxygen, and they consume it as they oxidise carbon. Cornell University’s compost chemistry pages put it plainly: oxygen gets used up and carbon dioxide is produced, so the supply has to be replaced. In an open heap you replace it with a fork. In a drum you replace it with a handle.
Enclosure matters for a different reason. The walls hold warmth in the middle of the mass. They also keep rats and foxes out. That second point is why I bought mine. Our old open bay sat against a hedge, and the local rat population treated it as a canteen.
Neither feature makes compost faster than the biology allows. A tumbler removes labour. It does not remove time.
Fill it two-thirds, and not a litre more
This is the most common way people break a tumbler. They cram it full.
A drum filled to the brim cannot tumble. There is no headspace, so the contents rotate as one solid slug, or they do not move at all. Air cannot get in. The middle goes anaerobic within days and the whole batch becomes a wet, sour brick.
Two-thirds is the working maximum. I go by weight now rather than by eye. On the 200-litre drum that is roughly 110 to 120 litres of loose material, which for a mixed load of kitchen scraps and shredded cardboard comes to around 40 kilos. Past that the handle gets heavy and the compost gets bad.
Leave room for another reason. A tumbler is a batch system, not a continuous one. If it is always full, Tuesday’s peelings have nowhere to go.
The drum that never gets turned
A tumbler that is not turned is just a bin with a handle on it.
I tested that by accident. One September I filled the small barrel, gave it two good spins, then ignored it for six weeks because work got busy. When I opened the hatch, the centre read 14°C. Effectively ambient. Nothing had happened. The material was recognisably the material I had loaded.
Turning frequency is not a fixed number. It follows temperature. A working batch sits between 90°F and 140°F, which is 32°C to 60°C, the band where Cornell’s compost temperature fact sheet says decomposition runs fastest. Above 140°F most of the organisms you want cannot survive.
So I turn on temperature, not on a calendar. Above 60°C, spin it that evening. Between 40°C and 55°C, spin every second or third day. Below 30°C with the moisture right, the batch is finished or stalled, and a weekly spin to check is plenty.
Daily turning is not better. It drives the heat out. Cornell’s guidance on compost safety treats 140°F as the point where turning becomes advisable, which makes it a trigger rather than a routine.
Greens and browns do not care about the container
This is the part the advertising elides. The carbon-to-nitrogen ratio inside a drum has to match the ratio inside a heap.
Cornell puts the ideal at about 30:1 by weight, and notes that below that figure nitrogen escapes as ammonia. Clemson University’s Home and Garden Information Center gives the same target while describing a workable band rather than one magic number. Most extension material settles on roughly 25:1 to 40:1 as the range where the microbes still function. I aim for 25:1 to 30:1, which is where the mixture heats reliably without stinking.
By volume the shorthand is two to three parts browns for every part greens. The US EPA’s composting guidance states exactly that proportion, and it is the version worth memorising because nobody weighs grass clippings.
Clippings are the usual wrecking ball. The Royal Horticultural Society warns that clippings on their own turn into a slimy, smelly mess, and advises mixing them with brown material as you add them. I stack mine beside the drum until there is enough shredded cardboard to match them.
Which brings me to the honest bit.
Spinning will not fix a bad mix
Rotation adds oxygen. It does not add carbon.
If a batch is mostly kitchen scraps and fresh clippings, the drum will smell whether you turn it twice a day or twice a fortnight. I have proved this more than once, most memorably with a load that was roughly four-fifths vegetable peelings. Ammonia and sour milk, at close range. The handle was doing nothing useful.
The fix was not more turning. It was two buckets of shredded cardboard and a dry load of autumn leaves, worked through by hand before the next spin.
Moisture, judged by hand
You do not need a meter. Squeeze a fistful taken from the middle of the drum. It should feel like a wrung-out sponge, which is the standard Virginia Cooperative Extension uses. A drop or two of liquid is fine. A steady stream means the batch is too wet. Crumbs that fall apart mean it is too dry.
Too wet is the failure I see most in tumblers, and it is a consequence of the design. Drums do not drain well, and they do not lose water to the air the way an open heap does. Water arrives with every bucket of peelings and has very little way out.
Dry batches are easier to correct. Add water while you turn, a little at a time, and stop as soon as the squeeze test passes.
When a tumbler goes sour
Rotten-egg and ammonia smells both mean the same thing. The batch has gone anaerobic.
University of Maryland Extension names tumblers specifically here, warning that an enclosed drum can quickly become soppy wet and anaerobic if you add too many kitchen scraps and not enough brown material. Overloading and wetness are the two levers, and they usually pull together.
My rescue routine is short. Tip the drum onto a tarp. Break up the matted clumps. Add coarse browns until the mix looks like breakfast cereal rather than porridge. Then put it back to two-thirds and resume turning on temperature.
The batch is rarely lost. It just restarts.
Litres on the box, litres you can actually use
Capacity claims deserve scepticism. A 200-litre drum holds 200 litres only when empty and stationary.
Filled to two-thirds it holds about 130 litres. Allow for shrinkage as the material breaks down and a working batch is closer to 110 litres of fresh input. That is the real number.
Now compare it with what a household produces. Our two-person kitchen generates roughly 4 to 5 litres of scraps a week. Add a fortnight of lawn mowings in summer and the drum is full within three weeks. Then it sits for two months while it finishes, and during those two months the peelings go in the wheelie bin.
That is the honest capacity problem. A tumbler suits small, steady inputs. It copes badly when you expect it to absorb a whole garden.
Two-chamber models get around this a little. You fill one side while the other cures. That is worth the extra money if you can find one in 200 litres or larger.
An honest timeline
Under good conditions a tumbler produces finished compost in about six to eight weeks.
State the conditions, because they are doing a lot of work in that sentence. Warm weather. Correct ratio. Moisture like a wrung-out sponge. Two-thirds full. Turned every second or third day. Take any one of those away and the clock stops.
For reference, UMD Extension gives hot composting a harvest window of six to eight weeks, while the RHS puts a conventional bin at six months to two years to reach maturity. A tumbler sits at the fast end of that range when it is managed, and at the slow end when it is not.
Winter is the honest exception. I started a batch in November two years ago. The drum hovered near freezing for months and the batch was usable in April. Cold does not stop the process. It puts it on hold.
Where an open bay beats a tumbler
Volume, mainly.
A three-foot cube holds about 765 litres. Virginia Cooperative Extension recommends a pile of at least 3 feet in each direction to run hot, and Clemson notes that piles smaller than that struggle to hold heat. Three feet is roughly a cubic yard. It is the minimum, not the target.
One autumn of leaves from a mature oak will fill a 200-litre drum several times over. Four loads, in my case, before I gave up counting and built a leaf mould cage. No drum in the consumer market will absorb a garden that size.
Bays also cope with material drums cannot. Long prunings. A whole courgette glut in August. You can push a fork straight into a bay, which is quicker than spinning a stiff handle on a cold morning with a full drum.
The trade-offs are real. Bays are open to rain and to animals, they take up more space, and they are slower unless you work at them.
What worm bins do that tumblers cannot
Worm bins and tumblers are not competitors. They process different materials.
A wormery takes kitchen scraps and produces castings. It does not want garden waste. Oregon State University Extension gives the sizing rule I use: about 1 cubic foot of bin space for each pound of kitchen waste added per week, and a bin no more than 1 foot deep because red wigglers live near the surface. The same source notes that vermicomposting is a cold process taking up to six months, and that it does not kill weed seeds.
University of Illinois Extension covers the same ground from the beginner’s side, and the RHS is blunt about scope. A wormery is an efficient way to deal with kitchen waste, and it is not a substitute for conventional composting.
In practice I run both. Scraps go to the worms through winter, when the drum is cold and idle. Garden waste goes to the drum. Almost nothing goes to landfill.
One caution from the University of Maine Cooperative Extension: manure, and dog or cat waste above all, carries a pathogen risk that a small home system will not reliably remove. Keep it out of a tumbler.
What I would tell someone buying a first one
Buy bigger than you think you need. A 100-litre drum is a boutique. It holds about 60 litres of working material, which is a fortnight of a small household’s scraps and no garden waste at all.
200 litres is the practical floor. 300 litres with two chambers is better if the budget stretches that far.
Check the hatch. Some models have a narrow mouth, and getting a spade or a gloved hand inside is miserable. Check the axle, too. A drum that flexes when full will leak liquid from the seam within a season.
Then accept the deal. You are buying convenience and rodent-proofing, not speed. The compost will take the time it takes.
And if the drum ever smells, do not go shopping for a better drum. Add browns. Dry it out. Turn it.