Last updated: August 7, 2021

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Composters have the task of producing valuable fertiliser from waste materials and with the help of soil organisms. An open composter supports this process by providing the necessary oxygen supply. On the other hand, the closed composter creates a much warmer compost environment. In addition to these two factors, there are many other things that need to be considered.

To give you an overview, we have listed the advantages and disadvantages of the respective designs of open and closed composters. Our composter test 2021 aims to help you with this purchase decision and to answer any questions you may have.




The most important facts

  • The composter provides optimal conditions for soil organisms to produce reusable fertiliser from garden and kitchen waste. Composting is therefore a more environmentally friendly alternative than going to the organic waste bin.
  • A distinction is mainly made between open and closed composters. The latter can be further differentiated into rotating/movable or stationary.
  • Open composters are usually larger, nicer and cheaper. Closed composters, on the other hand, compost faster, are more robust and less costly.

The best composter: Our picks

Buying and evaluation criteria for composters

Next, we will show you which aspects you can use to decide on a suitable composter.
Based on these criteria, you can compare composters with each other:

In the following paragraphs we will explain what you need to consider for the individual criteria.

Base & lid

In general, the composter should be placed on open ground if possible. This prevents waterlogging. Otherwise the water will collect and mould will set in. This also allows animals and microorganisms to enter the composter and decompose the compost.

If you want a composter despite solid ground, you can add soil organisms such as earthworms yourself or just buy a worm composter or Bokashi bucket directly. You can find out more about this in the guide under "What are the alternatives to composters?

If you choose a completely closed composter, you should water it on very hot days, otherwise it will dry out.

Frequent rainfall can make an open composter too wet. In this case, a mulch fleece would be advisable, which keeps the moisture at a reasonable level.

Speed

Depending on the type of composter, the composting process can be accelerated. Fast composters are particularly popular with amateur gardeners, as they take up very little space. Furthermore, they need less material to reach the right heat in contrast to open ones.

The thermal composter belongs to the subgroup of quick composters. This is able to store heat consistently due to its double-walled insulating construction.

Waste should be reduced in size in advance.

Another composter variant would be the drum composter. Here, the compost material is placed in a barrel-like structure and turned by a crank or by hand. The material inside is heated and aerated.

In addition to the composter itself, compost accelerators help with decomposition. They contain the nutrients that the soil organisms need for the decomposition process. Otherwise, the general rule is that the smaller the waste, the faster it decomposes.

Material, colour & shape

Basically, open composters are usually made of wooden pallets. Another type is expanded metal, which usually contains stainless steel or aluminium and has a grid-like structure. Wood in particular looks aesthetically better in the garden. On the other hand, it is more exposed to the weathering process than a closed composter would be.

Closed composters are usually made of plastic or metal. Since plastic is relatively flexible, it can lose its original shape over time. Metal is more durable, but even powder-coated metal can rust over time. Galvanised is more suitable in this case. They are often available in dark green, black and rarely brown, as this promotes the warming process and visually matches the garden.

The shape of the composter, i.e. whether it is round or square, is basically not very important. The only important thing is that there is enough space.

Rearrangement & chamber systems

Turning over the soil is a crucial part of composting. In this process, the bottom soil, which is now older, is moved upwards so that the new material has access to warmth and microorganisms. The whole compost receives a renewed supply of oxygen.

The process is supported by the choice of composter. A thermal composter, for example, has a flap underneath where you can directly access the already composted material.

As a rule, the composting process should be repeated every 4-6 months.

If you would rather not stratify at all or with minimal effort, a rolling composter would be for you. As the name suggests, it is rolled from one place to another with the help of its ball shape. The disadvantage is that it is not connected to the ground. The same applies to the drum composter mentioned in the "Speed" section.

With open composters, it is a good idea to add several boxes right next to each other in order to layer the compost from one container to the other.

Vermin & Odour

Many problems that arise during composting have more to do with the care itself than with the choice of composter.

If the right mix of oxygen, moisture and heat is present, no foul odour should develop. This balance can be disturbed if too much raw material is placed on top of each other. In this case, a larger composter is recommended.

Tip: If the composter is too wet, it is advisable to add dry branches.

Openings in the composter also often attract unusual garden inhabitants. In the case of large rodents such as rats and mice, an additional floor grid can prevent them from entering. Smaller animals such as ants, mosquitoes and flies are included in small numbers. In excess, however, it is advisable to sprinkle lime or gravel. This prevents rotting, which attracts the animals in the first place.

Size

Most composters are categorised according to their capacity in litres.

  • Composters with 250L-400L belong to the small sizes for composters in the garden and are mostly for small families, couples or individuals.
  • In the medium range are those between 400L-600L. Thermal composters are particularly suitable there.
  • The largest ones, up to 900L, are only suitable for very large households, when shared with neighbours or for those who keep several beds. In this size they usually come in open form.

If you are unsure about the size, especially because of a lot of leaves, you should buy a compost silo made of galvanised wire in addition to the composter for household waste. Of course, you can also collect it in the classic way as a heap.

As a general rule, it is better to buy 2 smaller composters instead of one large one. While one is being filled, the other can take a break.

Guide: Frequently asked questions about composters answered in detail

The guide contains essential questions on the subject of composters. It explains briefly and concisely what is helpful about composters.

What is a composter?

Composters are containers in which the composting process takes place. In the process, organic material is turned into humus by microorganisms with the help of oxygen. The decomposition process results in the release of valuable minerals for the garden.

Komposter-1

At the beginning of the decomposition process, we speak of raw humus. The most decomposed form, on the other hand, is called mulch. (Image source: herb007/pixabay)

Nowadays, a composter is used by both hobby gardeners and waste management. For example, compost can be produced from kitchen and garden waste.

How does a composter work?

The task of a composter is to support the composting process. To do this, it must be filled correctly. What is involved is described in the guide below.

Besides, the oxygen-nitrogen ratio must be in balance. The same applies to the moisture content.

If this is observed, the composting cycle takes place in three phases:

  1. At first, mostly mesophilic organisms (small animals with preferences for medium temperatures) participate. They break up the compost into finer material over a period of a few days.
  2. In the second phase, they are replaced by heat-loving organisms. The temperatures can become so high that even actually helpful helpers die off. This is counteracted by regrouping. Fresh air and new materials for decomposition are brought in. This phase lasts longer than the first.
  3. The last phase lasts the longest (several months). There, the temperatures drop continuously and mesophiles again take over the processing of what is left.

These phases are gone through to create compost from waste.

Who is a composter suitable for?

A composter is suitable for anyone with a garden. It may be a lot of work at first, but those who compost successfully will eventually be rewarded with high quality fertiliser.

Komposter-2

A pH value of less than 6.5 is harmful to worms.
(Image source: Sippakorn Yamkasikorn/ Unsplash)

Even without a garden, a composter is suitable, because houseplants also enjoy the nutrients. In addition to the potential fertiliser, the composter is a more environmentally friendly alternative than the organic waste bin.

What does a composter cost?

The price of composters varies greatly depending on the material and size.

Simple composters for smaller gardens and households can be found for around 20 pounds. These mainly include wire and cheap wooden composters. The majority are more in the range of 40 to 70 pounds.

What types of composters are there and which is the right one for you?

Composters are basically divided into two types:

Types of composters advantages disadvantages
Open composter larger, more accessible weathers faster, free access for animals
Closed composter rodent safe, faster more expensive, unnatural

In this case, open composters refer to those made of wood, while closed composters mainly refer to thermal composters.

Depending on the amount of compost, space and type as well as personal preferences, there are different advantages and disadvantages. To help you decide which model to choose, the next section lists the most important points of both composters.

Offener Komposter

Open composter

The advantage of an open composter is mainly its size. Despite a lot of compost material, it can be filled up quickly without ever having to remove a lid or squeeze the materials through a narrow gap.
The material of the composter has a natural look, but is also more susceptible to weathering. In addition, the spaces between the bars leave enough room for rats and mice.

Advantages
  • more practical with a lot of material
  • direct access
  • simple construction
  • cheaper
  • more natural
Disadvantages
  • more susceptible to rodents
  • composting process takes longer
  • wood weathers faster

Another big plus is the price. Because they are so simple to build, you can also craft one yourself.

Unlike the closed composter, there is no heat insulation. Therefore, it is important that there is enough material to produce the right amount of heat.

Geschlossener Komposter

Closed composter

The duration of the decomposition process is very much in favour of a closed composter. Those who want the compost as fertiliser for the garden are served much faster. Moreover, due to the small amount of raw materials produced by a small household, heating it from the inside would not be possible at all.

The lid also prevents any unpleasant odours. This is recommended for those who want to place their compost at the end of the plot. It also keeps all kinds of animals at a distance.

Advantages
  • keeps uninvited animals away
  • faster decomposition
  • no need to rearrange compost yourself
  • less prone to odours
  • takes up less space
Disadvantages
  • more expensive
  • more unnatural

Price-wise, the closed ones are in a higher price category than the open ones. If you are willing to pay more in the beginning in order to spend less time and energy on the conversion process, the purchase is well worth it. This is especially true for composting by hand crank.

Finally, it has to be said that not everyone finds the artificial look pleasant in the garden. On the other hand, closed composters take up less space.

What alternatives are there to the composter?

Besides the typical composter, there are other alternatives. The two alternatives are:

  • Bokashi bucket: Bokashi is the name for a method similar to composting. In the bokashi bucket, the raw materials are fermented, i.e. primarily converted into an acid mass without the inclusion of oxygen. Kobashi compost is only applied directly to beds after the pH value has been lowered.
  • Worm composter: Another indoor alternative for the balcony or flat is a worm bin. Compared to the garden, more soil organisms live in one space. To preserve this diversity, acidic fruit and chemically treated food in general should be avoided.

The two alternatives can also be used for disposal and for reuse.

How can I beautify the composter?

An unsightly composter disturbs the overall appearance of the garden. This does not have to be the case. The following products help to disguise the composter:

  • Pumpkins or courgettes in already decomposed compost
  • Nasturtiums
  • Sunflowers
  • Ivy

Stone walls are not recommended as they get in the way when rearranging and are more difficult to remove if the composter is enlarged.

How do I restack a composter?

Restacking is increasingly carried out at the beginning of spring. How this is done is explained in the following steps:

  1. Make room: If you only have one chamber, move all the compost from one side to the other on top for the first time. If you have two or even three chambers this is not necessary
  2. Sieving: Next, throw the compost through a large sieve using a shovel or fork. What does not fit through (usually branches, large stones as well as coarser compost) is used again later or removed.
  3. Replenish: The humus can now be used. Meanwhile, the composter is filled up with new materials.

In order to achieve the best possible turnaround of your composter, you should go through the previous steps.

How do I fill a composter?

To begin with, a composter is filled at the bottom with coarse material such as small branches and stalks. Then add garden and kitchen waste on top, followed by lawn and leaves. Fourth, a thin layer of compost and then again waste and lawn/leaves. On top another layer of compost, there should be seven layers in total.

Not all materials may end up in the compost without further ado. These include:

  • Meat
  • Dairy products
  • Pesticide treated or diseased plants
  • Cat litter
  • Oils
  • Coal
  • cooked food scraps
  • Weeds (if not yet dried out and seed bearers)

It is important to maintain the carbon (brown) to nitrogen (green) ratio of 20:1 on the compost. You can see what belongs to which category in the table:

type materials
carbon old hay, leaves, coffee grounds, cardboard, wood shavings
nitrogen vegetables, fruits, grass, flowers, algae

Products such as eggshells, paper, hair or nutshells should only end up in the compost in very small quantities. If you are unsure, it is better to be safe than sorry!

Where should I put the composter?

The best place is in partial shade and protected from the wind. Larger trees and shrubs are suitable. It is also important that the soil is freely accessible for the necessary microorganisms.

Komposter-3

For a large compost heap, excavators are used in waste management.
(Image source: Perkons / Pixabay)

When placing at the end of the property, maintain sufficient distance from neighbours. Remember that the further away the composter is, the more you have to walk every day. This can be inconvenient, especially in large gardens.

Image source: nikkytok / 123rf

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