Different Methods, Different Processes

The microorganisms that turn your kitchen scraps and lawn clippings into wonderful crumbly soil improver need three things to do their jobs properly:

• The right balance of carbon and nitrogen. Every successful compost pile needs a mix of carbon heavy (“brown”) material like dead leaves, shredded paper and cardboard, with nitrogen rich (“green”) material like kitchen scraps and freshly cut grass clippings. A great many composters fail by getting this ratio wrong, or not having enough of both “browns” and “greens”. (HelpMeCompost, Revolution Home Energy)

• Heat. Hot composting with properly thermophilic microorganisms (the ones that can survive and thrive at high temperatures) produces finished compost much faster than systems that never get hot. For the fastest possible turnaround time, aim for temperatures of 55-65°C (Allotment Book)).

• Oxygen. Aerobic composting requires plenty of airflow so these microorganisms can access the oxygen they need to turn your waste into compost. (Help Me Compost)

It’s also helpful to understand just how composting works, because there’s no point doing one of these methods if you don’t plan to do it correctly.

When you pile up garden waste and kitchen scraps, they’re not instantly transformed into compost. Instead, the microorganisms (mostly bacteria) that begin feeding on the material pass it through successive colonies in much the same way that food passes through your digestive system.

In practice, this works like so:

• The outer layers of leaves, veg peelings, grass clippings etc are eaten first.

• This provides nutrients for a generation of microorganisms, which then reproduce.

• When that first generation has consumed everything it can, it gets eaten by the next generation of even more hungry microbes.

• This continues until you’re left with something inedible: finished compost.

The speed at which this happens depends on those carbon: nitrogen ratios (always mentioned together because they’re a pair, like peanut butter and jelly) plus temperature and oxygen. As long as there’s enough food for all the microorganisms you introduce into the system, faster is better.

The fastest composting method is Berkeley hot composting, which advocates turning your pile every few days to introduce plenty of oxygen, monitoring temperature to track progress, and always having multiple piles in various stages of decomposition so you can harvest finished compost frequently. Getting everything just right is tricky, and at the time of writing there aren’t enough studies on small-scale (< 1 cubic metre) hot composting for certainty on best practices.

Open Heap Composting

The traditional pile of stuff at the bottom of the garden still produces compost faster and in greater quantities than any other method if you have the space and neighbours who don’t care about aesthetics. This is because it has zero capacity limitations. You can and should make an open heap as big as you like.

Three bay system. Set up three large heaps joined together with access to all three. Pile stuff into the first bay. When it’s full, stop adding new material and start filling the second bay. When the second bay is full, you let both of them finish composting while you add kitchen waste and garden waste to the third bay. Each bay should be roughly 4×4 feet.

You can build this entirely from reclaimed pallets for less than £50 including fixings and chicken wire to stop rodents trying to move in.

Management. The downside to open heaps is how much work they are to manage properly. Aerobic composting requires turning every few weeks to introduce oxygen. An open heap is huge physical effort to turn because a full bay contains several hundred kilograms of mixed organic matter. Using a compost fork, it takes me about an hour to properly turn one bay.

You also have to monitor moisture levels in the pile and add water during dry spells. Your heap should feel like a wrung-out sponge: damp, but not soaking wet. During prolonged periods of rain, the heap will benefit from a hessian sack or old carpet thrown over the top to protect it from becoming waterlogged.

Volume. The biggest advantage of open heaps is their ability to process any volume of material. Got a huge garden and produce several wheelbarrow loads of waste every week? You need an open heap. Producing enough material to fill one bay will be difficult for small gardens.

The autumn leaves that infuriate you by smearing all over your car in October? Save them for the compost. Good compost heaps can easily accommodate huge volumes of leaves.

Pests. Speaking of pests, your open heap might attract rats if you feed them scraps. Provided you manage the heap correctly by maintaining carbon: nitrogen levels and regularly turning the pile, rats should not become a problem. If you notice rats in your garden, adding more brown material and turning more frequently will deter them.

Rats aren’t your only potential problem. Birds like tossing through piles looking for food scraps. Use wire mesh across the base and lower sides to deter vermin. Depending on where you live, compost heaps can also attract cats that think they make good litter trays.

An honest appraisal of open heaps is that they are by far the best composting method in terms of volume, quality and cost. The issues of space and ongoing effort are frequently deal-breakers for people living in urban areas. Based on conversations I’ve had on social media, compost bins are the most common method in the UK.

Enclosed Compost Bins

If your main objection to open heaps is volume, or that your neighbours would murder you if you dump one on your lawn, compost bins are the obvious choice. That’s not to say closed bins aren’t without their drawbacks.

Capacity. Depending on your needs, make sure you get a bin that’s big enough to hold everything you want to compost. The budget compost bin I tested was 220 litres (BBC Gardeners World Reviews). This size holds about 4 months’ worth of waste from our suburban garden and allows for significant kitchen waste without overflowing.

If you produce more waste than this, you may need multiple bins or should strongly consider an open heap.

I strongly recommend bins with removable side panels. This will make it far easier to properly turn your compost. Not all bins have this feature.

Loading. Never load your bin like it’s a trash can. Always spread materials out and layer brown and green waste together rather than chucking in a shovel-full of grass cuttings or a bag of leaves.

The enclosed design of bins means less evaporation than open heaps, so you don’t need to add water as often. The lack of airflow also means it’s more important to get the moisture balance right. Bins become anaerobic and smelly quicker if they get waterlogged.

Turning. This is the biggest challenge with bins. Unless you have access to one with removable front panels, getting inside the bin to properly turn the materials is impossible.

One solution is to get two bins and rotate your compost between them every month or so. This gives excellent results and properly mimics the three bay system above.

I think bins are ideal for small gardens where a compost heap isn’t an option. They also work better than open heaps if you want to add food waste to your compost but don’t currently produce enough garden waste to fill a bin.

The tradeoff with bins versus open heaps is speed. You can still achieve hot composting temperatures in large bins if you feed enough material, but this is far more difficult than managing open heaps. Garden bins will still produce finished compost in 8-12 months if you keep on top of them.

Compost Tumblers

Tumbling side promises the best of both systems: fast results and easy maintenance. They deliver on speed of mixing, but once you start looking at conditions inside the average compost tumbler the marketing claims fall apart pretty fast.

Speed. Finished compost can be produced in a matter of weeks (HelpMeCompost), but the realistically achievable timeframe is 6-8 weeks (Better Homes and Gardens). That assumes you hit the ideal carbon:nitrogen ratio and moisture levels. For most people, those conditions only apply occasionally.

Mixing. This is where tumblers really shine. Regular, thorough mixing is the number one problem with static compost bins. When you can roll your compost like a knead bread every few days, nobody bothers not to.

The result is better aeration and much faster decomposition. Faster decomposition means less chance of unwanted smells.

Size. Compost tumblers max out at about 200 litres. This isn’t enough volume to get proper hot composting temperatures, so don’t expect speeds anywhere near 6-8 weeks. Plus, unless your activator goes by volume you need to load the tumbler all at once. Adding fresh material to an existing load drastically slows decomposition as the new stuff starts at day one.

You therefore need somewhere to store scratch until you have enough to fill the tumbler. The easier tumblers make turning should encourage you to compost more waste, but if you don’t modify your behaviour you’ll struggle to use them effectively.

Climate. The benefits of compost tumblers are dramatically decreased by the UK climate. Materials inside will cool far more often than elsewhere, which slows decomposition. They also get waterlogged far more frequently during our regular wet spells.

I find I need to add brown materials far more often with my tumbler during Autumn and Winter to stop it becoming a sour sludgy mess.

Cost. Good tumblers are expensive. UK average is £150-£400 compared to around £80 for a decent compost bin.

The plastic wears out. Rotating mechanisms break after 3-4 years in some cases. Cheaper models leak badly and have nearly impossible to use rotation systems.

If you don’t generate enough waste to fill a compost bin each year, don’t bother with a compost tumbler. They work well if you follow the instructions and are prepared to throw loads away when it all goes wrong (as it sometimes will). Just don’t expect the advertising hype.

Common Mistakes

Mistake #1: Loading your bin like a trash can. Everyone falls for this trap when they get their first compost bin. A 150 litre bin feels like plenty of space until you add two weeks’ worth of kitchen waste then suddenly it’s full. Twice as big is better.

Mistake #2: Grass clippings with no brown material. Unless you have unlimited supplies of dead leaves to mix in, avoid adding lawnmower waste on its own. Grass clippings are heavy with nitrogen and quickly rot to a disgusting smelling liquid mess. You need plenty of carbon rich materials to absorb moisture and balance out compost heaps moisture levels.

Mistake #3: Believing compost tumblers are magical boxes that work without effort. Adding layers of green and brown material, monitoring moisture levels, turning regularly. These are all still necessary with a tumbler.

Research Basis

Home composting is an area of lifestyle permaculture that’s interestingly devoid of research. Despite the ready availability of small-scale systems perfect for use in academic trials, there are almost no UK based studies that look at variables like system type.

Commercial composting operations are studied far more frequently, but while the equipment may be similar the volumes we’re dealing with at home are tiny by comparison.

We do know that temperature is the biggest variable between hot and cold composting. Time to finished compost is roughly half as long when average temperatures inside reach 55-65°C.

We also know that what actually happens inside these bins isn’t well understood. Only one study I could find (MPI) looked specifically at microorganisms found in home compost bins. It found there were still massive knowledge gaps despite being conducted over a decade ago.

The obvious question then is how system type impacts decomposition rates. Does it? Frankly, no evidence suggests one way or another.

We do know aerobic decomposition is more efficient than anaerobic (FAO), so a container that makes turning difficult is going to produce inferior compost to one that’s easily managed.

We also know the ideal carbon: nitrogen ratio and moisture levels (University of Florida). Getting enough air into a tumbler is vastly more difficult than throwing down a compost heap.

The other big question is about volume. Higher volumes mean greater heat retention (helpful for hot composting) but also restrict airflow. Would more tumblers solve that issue, or simply produce compost slower than a well maintained heap?

The research just isn’t there to say. From personal experience and talking to others who compost I can tell you well managed heaps almost always outperform bins or tumblers. Without research backing that up I can only suggest it’s due to how much easier they are to manage properly.

We know from multiple sources that temperature is the biggest difference between fast and slow composting. Yet most tumblers in the UK will never achieve temperatures needed to reach those timelines.

Final takeaway from the lack of research available: get the basics right and you’ll produce good compost no matter what system you choose.

When Composting Methods Don’t Apply

• Flat dwellers with balconies: Skip all three of these methods. Small electric composters or wormeries are a better choice.
• Shared gardens/allotments: Open heaps or large bin systems. With multiple people contributing you’ll always have enough volume to get hot temperatures, and plenty of people to do the turning and feeding.
• Rural properties with land: Heaps. Neighbours aren’t an issue when you’re surrounded by fields. Want to hide your heap behind a large hedge? No problem.
• Rented properties:Bins. They’re portable and don’t require permanent structures.
• High maintenance gardens: If your property produces enough prunings/lawn clippings to fill a wheelbarrow each week, you need heaps or multiple bins. A single tumbler won’t deal with that sort of volume.

Benefits of Composting at Home

• Reduces household waste: Home composting accounts for between 20-30% of your total household waste that would otherwise go to council collections. For people paying per collection, that’s direct savings.

• Makes your soil better: There’s no substitute for homemade compost when it comes to improving soil quality.

• Save money: Good quality compost costs £3-£5 per 40 litre bag at the garden centre. Even assuming you’re not actually using that much compost around your garden, a functional compost system is creating the equivalent of £50-£150 worth of garden residues every year.

• Helps the planet: Does it really? Your compost saves that methane emissions from landfills and reduces transport emissions by not buying bags. On its own? Not by much. But it’s one less thing you’re not doing.

• Improves garden health: Fewer pests and diseases since adding compost supports beneficial organisms.

• You’ll learn about soil biology.

TL;DR Version

Step 1: Choose your composting system. Do this during week 1.

If you’re serious about composting long-term, spend a little more and get two bins. Unless you have a huge garden you won’t get enough volume for hot composting temperatures in a heap or single bin. Get your brown materials ready. Use fallen autumn leaves!

Step 2: Set it up and start loading. Week 2-4.

Don’t dump food waste in one go. Load your bins (or heap) like you would any compost pile by adding brown materials with every load of kitchen waste. Garden residues like lawn cuttings/clippings and excess leaves need bulking material too.

Add water if the compost looks too dry, but don’t drown it. Begin saving food waste in a container next to your kitchen bin. Every 2-3 days, add this to your compost.

Step 3: Work out how often you need to turn your compost and get into a routine. Months 1-6.

Its also important to plan for how you’ll manage your system once the novelty wears off. Home composting is a marial job like any other gardening task.

If you stop bothering it will decay to a rotten mess. Make turning/removing bins or rolling your tumbler part of your routine. Soon you won’t even notice it’s a chore.

Budget:

Total: £35-£430 depending on method chosen.

Step 4: Monitor your system and tweak it until it’s turning out finished compost regularly. Months 3-6

You’ll know when it’s working correctly. Macroscopic stuff will be visible to the naked eye, but your compost will also have an earthy smell rather than rotten. Use a fork to check compost readiness.

If it’s ready, great! You’re done. Add some of your finished compost to your new load so good bacteria have something to eat.

If not, look at what might be wrong and adjust moisture levels, browngreen balance or turning frequency until it is.

Step 5: Harvest your finished compost and apply it to your garden. Months 6-18+

How long this step takes depends entirely on which system you chose and how good you’ve become at compost management. Even “failed” loads aren’t wasted, they’re just fed back in to speed up decomposition of fresh material.