Composter purchasing advice: how to choose the right product

  • What You Need to Know
  • In the compost, organic waste is transformed into useful compost.
  • Open composters take up a lot, but are exposed to the weather, which can delay decomposition.
  • Closed thermal composters are designed for heat insulation.
  • Waste decomposes much faster in thermal composters.

Free and environmentally friendly waste disposal

Both the garden and the household produce waste that is biodegradable. Many garden owners take advantage of this by disposing of organic waste in a compost heap. They are collected in a wooden rack and left to rot. In this way, valuable fertiliser is created for flower and vegetable beds.

In a classic, open compost heap, the decomposition process takes a good year. This type of composting therefore requires patience and labour, which not every garden owner can afford. An alternative to the conventional pile is the closed quick or thermal composter made of plastic. Due to its heat-insulating properties, waste inside it decomposes into compost after only a few months.

Open or closed composter?

One thing in advance: both variants of the composter deliver the same product in the end. However, proper composting is a prerequisite for this. The space available in your garden and the waiting time you are willing to put up with are the decisive factors in your choice.

The open composter

The open frame made of wood or plastic is probably the best-known form of composter. To ensure sufficient ventilation, gaps are left between the wooden slats. The open construction offers some advantages. It is equally suitable for people who only put something on the compost now and then, as well as for gardeners who have large quantities to compost. The design allows the waste to be easily turned over with a pitchfork. When it rains, the open composter can be covered with a tarpaulin.

A filled composter in the garden
The open composter is a common sight in gardens.

The principle of the open compost heap has proven itself over centuries, but the construction method also brings with it some disadvantages. Wood, for example, inevitably rots, even if it has been specially pre-treated. After five to ten years, the construction must be renewed. Since the activity of the microorganisms in an open composter depends on the weather, it usually takes a little more than a year before usable fertiliser is produced. The microorganisms are responsible for the decomposition of the waste. Finally, aesthetics also play a role for many garden owners. An open compost heap is not a pretty sight and may smell unpleasant. It is therefore less suitable for smaller gardens, as the owners will inevitably be in the vicinity of the composter.

Pro points

  • Simple composting
  • Low costs


  • Slow decomposition of organic waste
  • Possible odour nuisance
  • Renewal necessary for wooden models

The quick or thermal composter

Thermal composters are closed compost bins made of plastic with a closable opening and ventilation slits in the walls. They are usually dark coloured so that they absorb a lot of solar heat. High-quality models also have thick plastic walls that are optimised for heat insulation. Quick or thermal composters are thus designed to generate as much heat as possible inside to speed up the decomposition process. Temperatures of up to 70 degrees Celsius are reached in them. Since they remain warm even on cold days, the microorganisms that recycle the waste can work continuously. As a result, thermal composters provide valuable fertiliser particularly quickly.

A closed quick composter in the garden
The thermal composter promises a fast production of compost.

Composters are usually quick to set up: put four walls together, put the lid on – and you’re done. Particularly tidy garden owners are also spared the sight of a compost heap, which is not to everyone’s liking. The smell is also kept in check by the closed construction. When filled properly, however, compost does not smell foul. Due to the material, thermal composters are much more durable than open wooden constructions.

Pro points

  • Usable for decades
  • Hardly any odour nuisance
  • Fast composting


  • More expensive than an open composter

What you should look for when buying a composter

A quick or thermal composter is ideal for a smaller home garden. For large gardens that produce a lot of garden waste, a compost heap is probably the better choice. Thermal composters must not be overfilled and it must be possible to rearrange the pile at any time.

Choice of material – wood, plastic or metal?

Some materials are more common in certain composter designs than others. In most cases, the classic open composter is made of wood. Since thermal composters should store heat as well as possible, they are made of plastic. Many manufacturers use click and plug systems for their composters, so that assembly can be done quickly and without tools. This construction is common for both wooden and plastic composters. Some thermal composters in barrel form only need to be set up.

Wood is a natural, renewable raw material and visually fits well into a natural and rustic garden. If necessary, wooden composters are easy to repair even by people with little craftsmanship. The disadvantage is that even treated wood participates in the process of rotting. The construction thus loses stability and must be replaced sooner or later.

Plastic has the advantage that it is durable and does not rot. This means that plastic composters can be used for many years. Another advantage is that they are easy to move around. In addition to closed thermal composters, open models made of plastic are also available. Those who value sustainability should buy a composter made of recycled plastic. However, once the plastic composter has had its day, it must be disposed of at a recycling centre.

Metal composters may look fancy, but they are not recommended. They are heavy and can start to rust over time. In the process, the material releases harmful substances into the compost.

composter of wood and plastic
It can be useful to have both types of construction in the garden.


Even in small gardens, large quantities of prunings, leaves and other waste accumulate. The capacity of the composter should therefore not be too small for your garden. Common volume sizes are 400, 600 and 900 litres.

A composter with a capacity of 200 to 300 litres is sufficient for small gardens and also holds the kitchen waste of a family of three.

For medium-sized to larger gardens and a household size of four people, a composter with a volume of 500 to 900 litres is suitable.

Very large composters with a capacity of more than 900 litres are designed for particularly extensive gardens.

Chop the cuttings

If you have a lot of prunings in your garden, it is advisable to buy a shredder. Branches and twigs must be shredded before they are composted. Otherwise they take a long time to rot.

Air circulation

An important criterion when choosing a composter is the type of ventilation. Without a sufficient supply of air, the organic waste will not only rot very slowly, but mould can also form. If the compost starts to rot, it is no longer usable.

The conventional open composter has large gaps between the slats that allow good air circulation. With thermal composters, on the other hand, it is sometimes not directly obvious how the air circulates. There are ventilation slots and holes in the walls and sometimes also in the lid. Ventilation through wall slats is also common. Basically, a thermal composter is less permeable than an open composter, as the aim is to create as high a temperature as possible inside it. Both composters must have direct contact with the ground so that the air also reaches the contents from below.

Filling and removal

Composters are filled from above. This is no problem with the open constructions, as they are large enough for this. In the case of thermal and rapid composters, the loading flap should be large enough so that they can be filled comfortably and no waste falls beside them. A hinge is also helpful so that the composters cannot be opened by the wind or by children and animals.

In open composters, depending on the design, the fertiliser is simply removed with a pitchfork or via a flap near the bottom. These removal flaps are standard on thermal composters.

This is how organic fertiliser succeeds

Composting is not a science, but you should not do it too carelessly either. If you prepare the compost correctly and use suitable waste, you will get the useful, natural fertiliser after some waiting time.

Requirements for successful compost

For the compost to succeed, the composter or its contents need direct contact with the soil. This is how earthworms and other helpers find their way directly into the organic waste. The compost also needs warmth, moisture and oxygen.

Heat promotes the decomposition processes in the composter. Although it is also absorbed from the outside, most of the heat is generated inside when the waste decomposes. A thermal composter retains the heat, which is why decomposition does not come to a standstill even in winter.

There should always be a certain amount of moisture in the composter. As a rule of thumb, the contents should be about as wet as a squeezed sponge. Dry clippings will not decompose in the composter, because the microorganisms and soil organisms only work when there is moisture. This is why it is sometimes necessary to water the compost with a watering can. However, the compost must not get too wet, otherwise the waste will start to rot. Thermal composters have the advantage that the lid protects the contents from rain. Consequently, you should cover an open composter with a tarpaulin in case of heavy and prolonged rain.

After all, the organisms in the composter need oxygen to do their work. The grooves in the outer walls of the composter provide enough aeration.

Where should the composter be placed?

The location is also crucial for the success of the compost – especially in an open composter. To prevent drying out or rotting, it is advisable to place the compost in partial shade. It is a good idea to place the compost behind the garden shed or a hedge. Be considerate of your neighbours: the composter should have sufficient distance to terraces and houses. Both closed and open composters need direct contact with the soil so that soil organisms can reach the compost material. A composter on a paved surface may look neater, but it prevents microorganisms from reaching the compost through the soil.

Waste suitable for composting

In principle, a wide range of household and garden waste is suitable for composting. This includes, for example, vegetable and fruit residues, eggshells, orange and lemon peelings, coffee and tea filters, dry leaves, lawn and shrub cuttings and wood shavings. However, be careful not to put mouldy waste on the compost. Meat or cooked food scraps are also taboo, as they attract rats. Be careful not to accidentally compost weeds that spread via the roots. They sprout in the compost and spread their seeds in the soil.

These things can go into a composter
The organic materials shown here are well suited for composting.

To fill the composter

You have a lot of freedom when filling the composter. A colourful mixture of different waste is beneficial to the work of the soil and microorganisms. For a good yield, you only need to follow a few basic rules. Fill the lower part of the composter with coarse materials so that the air can easily penetrate to the top. Mix dry waste with wet and fine with coarse. Add carbon rich and nitrogen rich materials to the compost. These elements promote growth and are particularly good in the finished fertiliser. Vegetable waste and lawn clippings contain nitrogen, leaves contain carbon. Rapidly decaying and muddy waste should be added at a maximum height of ten centimetres. To avoid odours, sprinkle rock flour or soil on top.

Accelerator for your compost

If the decomposition processes in your composter are slow to start, you can help with compost accelerators. These powders usually consist of nitrogen, potassium, bone meal and, above all, microorganisms and fungi that kick-start the composting process.

How often does the compost need to be turned?

The mixing of the compost waste is called “turning”. To prevent rotting, an open compost must be turned at least once a year. Most garden owners mix their compost more frequently.

For turning an open compost heap you need a pitchfork, a shovel and a compost sieve. The work should be done on a dry day. The entire contents of the compost are passed through the sieve. What falls through the sieve is mature compost, all remaining waste must be left to mature.

Repositioning is also necessary with a thermal composter, although less frequently. It is recommended to rearrange the contents three to four weeks after a fresh filling. This is much easier than with open compost. To do this, open the lower removal flap and fill in the compost again at the top. This mixes the contents and aerates them sufficiently.

Recognising mature compost

At the end of the composting process is the finished fertiliser. But how can you tell that the compost is ripe? Finished compost is fine-crumbly, dark brown to black and smells like forest soil. If you are not sure whether the soil is usable, you can carry out the so-called cress test. Cress reacts sensitively to high nutrient levels and thus indicates whether the compost soil is ripe. For the cress test, take several samples from the composter for comparison, fill them into trays and sow cress. You can compare the germination results after just four to five days. If the plants form lush green leaves and straight stems and do not turn brown or yellow, the compost is ready.