Composting correctly: why temperature is so important in your compost heap

A well-maintained compost heap transforms garden waste, leaves, grass clippings and kitchen scraps into valuable humus. For this natural process to work reliably, however, the right materials alone are not enough. Moisture, oxygen, material mix and, above all, temperature determine whether high-quality compost is produced from organic waste. By monitoring the temperature regularly, you can quickly see whether your compost is actively working or whether adjustments are needed.

What happens during composting?

During composting, microorganisms, fungi, small organisms and soil life break down organic material. Fresh plant residues gradually turn into dark, crumbly and nutrient-rich compost that improves soil structure and supplies plants with important nutrients. For this process to run optimally, microorganisms need a balanced ratio of nitrogen-rich and carbon-rich components.

Nitrogen-rich materials include fresh grass clippings, vegetable and fruit scraps, and young plant residues. Carbon-rich materials include dry leaves, shredded branches, straw, wood chips or small amounts of cardboard. When these materials are mixed well, a loose structure is created in which air can circulate. This oxygen supply is essential to ensure that the compost does not rot, but decomposes cleanly.

The most important rules for a healthy compost heap

1. The right mix of green and brown material

A common composting mistake is using a one-sided material mix. Too much grass clipping can compact the heap and encourage rot. Too much dry material, on the other hand, slows down the composting process. A varied mixture of moist, nutrient-rich components and dry, structure-giving materials is ideal.

2. Ensure sufficient oxygen

Compost needs air. If the heap becomes too compacted, oxygen-poor areas can develop. These may produce unpleasant odours and slow down decomposition. You should therefore loosen the compost regularly or turn it over. Especially with larger compost heaps, it is useful to mix in coarser structural material such as small branches or shredded material.

3. Pay attention to the right moisture level

The compost should be moist, but not wet. As a simple rule of thumb, the material should feel similar to a wrung-out sponge. If the compost is too dry, microorganisms work only slowly. If it is too wet, oxygen is lacking and rot may occur.

4. Check the temperature regularly

Temperature is one of the most reliable indicators of whether the composting process is active. If the temperature inside the heap rises, this shows that the microorganisms are working intensively. If the compost remains cold, this may indicate too little moisture, too little nitrogen, insufficient aeration or a compost heap that is too small.

Why is temperature so important when composting?

An active compost heap goes through different temperature phases. After the heap is set up, the warming phase begins. With a good mix and sufficient moisture, the temperature inside can rise significantly. During the hot composting phase, organic components are broken down particularly quickly. At the same time, a sufficiently high temperature can help reduce germs, pathogens and many weed seeds.

Especially in hot composting, temperatures of around 55 to 65 °C are an important sign of active decomposition. If the compost becomes significantly too hot, microbial activity may decrease. If it remains too cool over a longer period, the process slows down. For this reason, it is useful not to rely solely on feeling, but to measure the temperature in a targeted way.

Typical temperature ranges in compost:

• Below 30 °C: The compost is not very active or is in a cool initial or maturation phase.

• Approx. 30 to 45 °C: The composting process is active, but not yet in the hot phase.

• Approx. 45 to 65 °C: The compost is working intensively; this is a good range for hot composting.

• Above 70 °C: The heap may become too hot; turning or aerating it can help.

Compost thermometer: a practical tool for better results

With a compost thermometer, you can measure the temperature directly inside the heap. This is important because the surface is often much cooler than the core. From the outside, it is therefore difficult to judge whether the compost is really active.

A thermometer with a long probe is particularly practical, as it also allows you to reach deeper areas of the compost heap. The dial compost thermometer with stainless steel probe, 500 mm, is ideal for monitoring garden compost, hot compost and larger compost heaps:

https://priggen.com/Zeiger-Kompostthermometer-Edelstahlsonde-500mm

The long stainless steel probe allows measurements in the core area of the compost, while the clear dial scale makes it easy to assess the temperature quickly.

The thermometer measures within a range of 0 to +100 °C and features colour-coded temperature zones. This allows you to see at a glance whether your compost heap is warm, active or hot. It makes temperature monitoring simple and reliable, even without digital measuring technology.

How to measure compost temperature correctly

Insert the probe as deeply as possible into the compost heap, ideally into the core area. Wait briefly until the display stabilises. For larger heaps, do not measure in just one place, but at several points. This gives you a realistic picture of whether the composting process is running evenly.

Directly after setting up the compost heap, it is advisable to check the temperature regularly. If the temperature rises within the first few days, this is a good sign of active microbial decomposition. If the temperature drops again later, this may indicate that the compost should be turned, aerated or supplemented with fresh material.

What should you do if the compost does not heat up?

If the compost heap remains cold over a longer period, there may be several reasons. Often the heap is too dry, too small, layered too loosely or contains too little nitrogen-rich material. Excessive compaction can also slow down the process because too little oxygen reaches the inside of the heap.

Possible measures if the temperature is too low:

• Lightly moisten dry material.

• Mix in fresh, nitrogen-rich components such as grass clippings or plant residues.

• Loosen compacted areas with a digging fork.

• Increase the size of the compost heap so that more internal heat can develop.

• Cover the heap during heavy rain to prevent it from becoming waterlogged.

What should you do if the compost becomes too hot?

If the compost becomes too hot, this can affect the activity of certain microorganisms. In this case, it usually helps to turn the heap and mix in fresh, structure-rich material. This brings oxygen into the compost, distributes the heat more evenly and allows the composting process to continue in a more controlled manner.

How can you recognise mature compost?

Mature compost is dark, loose, crumbly and has a pleasant earthy smell. The original components are hardly recognisable. Temperature is also an important indicator: when the compost cools down after the hot phase and approaches ambient temperature, it is entering the maturation phase. Before being applied in the garden, the compost should be well matured so that plant roots are not affected by immature decomposition products.

Conclusion: measure temperature and control composting more effectively

Correct composting is not a matter of chance. If you keep an eye on material mix, moisture, oxygen and temperature, you can control the decomposition process much more effectively and obtain high-quality garden compost more quickly. The temperature reliably shows whether the compost is active, whether it should be turned or whether it has already entered the maturation phase.

For simple and direct monitoring inside the compost heap, a robust compost thermometer is a useful tool. The dial compost thermometer with 500 mm stainless steel probe helps you reliably monitor the temperature inside your compost and better assess the composting process:

https://priggen.com/Zeiger-Kompostthermometer-Edelstahlsonde-500mm