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compost-thermometer

The UK's bestCompost Thermometers2022 Review

What To Look For in a Compost Thermometer

Composting at home is immensely satisfying, but it can be hard to get right. The most common questions we see are “When should I turn my compost?” and “How do I know if it’s ready to use?”. 

Compost thermometers are the answer. The best compost thermometer will be made from stainless steel as it won’t rust when exposed to warm, moist environments. A 40 – 50 cm probe length is recommended, to reach the middle of the compost heap, and a temperature range up to 80°C (measured in 1 – 2°C increments) is sufficient for an accurate reading. 

Top tip: If compost goes above 70°C, it will be too hot for the bacteria to continue the composting process.

Also, not all compost thermometers go down to 0°C, but it can be worth looking out for if you want to compare the inside and outside temperature of the compost over winter. You should make sure that the thermometer is in units that you are comfortable understanding. Many compost thermometers display readings in either Fahrenheit and Celsius, so double check you’re happy with the units before buying one.

Additionally, if you want to read temperatures at a glance, you might want to look for a compost thermometer with a coloured dial – these quickly indicate how the compost is faring without having to check the exact temperature. One final thing, that helps prevent fogging, is a dial that’s hermetically sealed. Not all compost thermometers have this feature, but it can help reduce moisture ingress.

Overall, my top recommendation is the Green Wash Compost Thermometer. This stainless steel thermometer has a 40 cm probe, a 50mm dial and a clear display. The display features contrasting black writing against the silver steel face, with a long needle that makes it easy to read accurately. It measures a wide range of temperatures, from -10 – 90°C, in 2°C increments. 

Check out the reviews below for more information on this compost thermometer as well as some other great alternatives.

See the best Compost Thermometers below

Compare Compost Thermometers Here

Use the dropdown to sort the table by the feature that's most important to you.

  • Our score
  • Best For
  • Temperature Scale
  • Celsius or Fahrenheit
  • Probe Length
  • Dial Width
  • Waterproof
  • Material

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Read Our Compost Thermometer Reviews

B0036DCVB4
4009816380449
Best for below 0 temp.
Green Wash Compost Thermometer
Top Pick

Best for below 0 temp.

  • Where to buy
  • Our Scoring
    Ease of Reading
    Accuracy
    Value for Money
    Overall
    3 4.4333333333333
  • Temperature Scale
    -10 to +90°C
  • Celsius or Fahrenheit
    Celsius
  • Probe Length
    40 cm
  • Dial Width
    50 mm
  • Waterproof
    No
  • Material
    Stainless steel
  • Our Review

    Taking the guesswork out of the composting process, this Green Wash Compost Thermometer gives an accurate reading making it easy to know when to turn the compost.

    The body has a stainless-steel construction which means it’s rust-resistant and protected from any moisture in the heap. Therefore, the 40 cm probe remains rust free even if it is frequently exposed to humidity. However, leaving it out in the all weather conditions can cause condensation to build up, which may affect the reading, so it does need to be kept reasonably dry in general.

    If you’re nervous about letting heat escape from your compost, the thick stem is long enough to put through any vents in your compost tumbler or bin, meaning you can take a reading without having to open it up. Otherwise, it’s a good length, and strong enough, to easily push into any compost pile, clearly displaying the reading on its 50 mm dial.

    This large dial is big enough to read without having to remove the thermometer from the compost, and the black writing contrasts against the silver steel face making it easy to read. It shows the compost’s temperature in Celsius.

    As mentioned, the one primary flaw of this compost thermometer is its susceptibility to condensation. This can make the display difficult to read, so the importance of keeping it dry can’t be overstated. It also only shows the temperature in Celsius, so you might find this isn’t the best compost thermometer for you if you prefer using Fahrenheit.

    Nevertheless, it’s one of the best compost thermometers if you’re looking for an accurate reading. Also, the clear black-and-silver dial has a particularly well-designed scale that is intuitive and easy to read. Whereas some compost thermometers can give ‘approximated’ results, this gives an accurate temperature reading and is reliable as long as it is well looked after.

    Pros

    • The large dial allows you to read the compost's temperature without removing it from the soil
    • The long probe is suitable for most compost bins and can be inserted through vents if needed
    • Reacts quickly to temperature changes
    • The stainless steel construction is good quality and, provided it is stored correctly, should last a very long time

    Cons

    • Dial isn't hermetically sealed which means moisture can get in
    • Any condensation inside will make this thermometer difficult to read
    • Not waterproof so shouldn’t be left outside in exposed areas
    • The dial only shows Celsius and not Fahrenheit

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B01E5PS61U
5024368182395
Best compost thermometer
ETI Ltd Stainless Steel Compost Thermometer
  • Where to buy
  • Our Scoring
    Ease of Reading
    Accuracy
    Value for Money
    Overall
    3 4.6333333333333
  • Temperature Scale
    0 – 100°C
  • Celsius or Fahrenheit
    Celsius
  • Probe Length
    50 cm
  • Dial Width
    50 mm
  • Waterproof
    No
  • Material
    Stainless steel
  • Our Review

    Some compost thermometers can be surprisingly expensive, so if you’re looking for a reasonably ‘budget’ option that will still give a good reading, this ETI Ltd Stainless Steel Compost Thermometer is cheap yet sufficiently accurate.

    Its 50 mm dial has a clear display with three coloured zones (representing ‘warm’, ‘active’ and ‘hot’). This colour coding makes it easy to tell, at a glance, how the compost is performing. Alongside this, it has a wide temperature range of 0 – 100°C.

    When it comes to temperature accuracy, this composter thermometer shows readings to +/- 2°C; however, for anyone who is just starting out with hot composting, this will likely be as accurate as necessary. Plus, for the price, an accuracy of +/- 2°C isn’t too surprising or disappointing.

    It can take a little while to display a reading, so the 50 cm probe needs to be left in the compost for some time in order to show the right temperature. However, like most compost thermometers, despite its stainless-steel construction, the display itself is not completely water-resistant, so it shouldn’t be left in the compost permanently.

    Condensation can get inside the dial if the compost thermometer is exposed to water like rain or too much humidity.

    The compost’s temperature is shown in Celsius only, and the display is generally easy to read. That said, the 1°C increments are small, and likely difficult to see accurately from a distance. The colour zones do make it simple to quickly understand how your compost is fairing, though, without needing to see specific temperatures.

    As a result, this is an ideal compost thermometer for those who are most comfortable with Celsius but also want to quickly see how compost is performing at a glance. The easy-read colour-coded dial makes it intuitive to understand quickly. It’s also the best compost thermometer to buy on a budget, giving a good indication of how your compost is doing without requiring a large investment.

    Pros

    • The 50 cm long probe means this thermometer can get right into the middle of most compost piles
    • It’s easy to see at a glance whether your compost is in the warm, active or hot zone
    • The accuracy is sufficient for measuring compost - at about +/- 2°C
    • Sturdy and durable stainless steel build

    Cons

    • The inside of the dial may fog up with condensation which makes it difficult to read accurately
    • Accurately reading the dial may be tricky for some users as the writing is quite small
    • Dial isn't hermetically sealed which means water can get in
    • The probe is relatively easy to scratch
    • It only displays the temperature in Celsius

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B00KXAGST4
0885468150159,4202250097328,0784672337717
Best dial design
Cate's Garden Compost Thermometer
  • Where to buy
  • Our Scoring
    Ease of Reading
    Accuracy
    Value for Money
    Overall
    3 4.4
  • Temperature Scale
    40 - 180°F
  • Celsius or Fahrenheit
    Both
  • Probe Length
    50 cm
  • Dial Width
    50 mm
  • Waterproof
    Water resistant
  • Material
    Stainless steel
  • Our Review

    If you’re serious about composting, you might be looking to spend a bit more money on premium tools. Unlike the other thermometers featured here, this Cate’s Garden Compost Thermometer is water resistant and has a hermetically sealed dial that will prevent fogging.

    It has a water-resistance rating of IP55, which officially means it is protected from dust and water jets (just not immersion in water). In practise, this results in a compost thermometer that is more resistant to condensation than the others on this list.

    The 5 cm dial is clear enough to read, with three different ways to interpret the information: there’s a dual temperature scale, so you can read the temperature in both Celsius and Fahrenheit, or you can use the colour-coded zones to quickly see if your compost is ‘warm’, ‘active’, or ‘hot’.

    However, it is worth mentioning that the Fahrenheit scale is more intuitive than the Celsius one, and this Cate’s Garden Compost Thermometer may have been designed primarily for a Fahrenheit-savvy audience. The Fahrenheit scale starts at 40 and rises in 20°F increments, whereas the Celsius scale displays numbers that rise in 11°C increments. This is a little unusual and can take a bit of getting used to.

    In terms of construction, the metal exterior and probe are both made from 304-grade rust-resistant stainless steel. Another tick for this thermometer’s weather resistance.

    At 50 cm, the probe is a good length for either a compost bin or heap, being long enough to stick into the centre and find the hottest areas. It doesn’t have a particularly thick stem, though. On the one hand, this can help it better get through compacted matter, but on the other hand care needs to be taken so as not to damage the probe in dense compost piles.

    Overall, due to its hermetically-sealed dial, stainless steel construction and colour-coded face, this is one of the best compost thermometers if you want something that’s easy to interpret, hardwearing and won’t fog up. However, as mentioned, whilst the Cate’s Garden Compost Thermometer shows both Fahrenheit and Celsius, it’s slightly more intuitive if you use Fahrenheit.

    Pros

    • Measures in both Celsius and Fahreneheit
    • The long probe can be pushed into the very middle of most compost piles
    • Three colour zones on dial quickly indicate whether compost is warm, active or hot
    • Construction is stainless steel which is rust resistant
    • Hermetically sealed dial so will avoid fogging and moisture ingress

    Cons

    • The stem is lightweight and a little thin, so care is needed when pushing it into a compacted compost heap
    • Too much sunlight may discolour the screen
    • The scale is a little tricky to read if you are used to a standard Celsius thermometer, but easy for reading Fahrenheit

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How to Choose The Best Compost Thermometer

Monitoring the temperature of your compost is the best way to ensure efficient composting and quality results.

By knowing when your compost heap is heating and cooling, you’ll be able to turn it at the appropriate time during its heating cycle. This is how to achieve optimum results and wonderfully nutritious compost.

Therefore, a thermometer is a valuable piece of compost equipment. Compost thermometers also indicate when your compost pile has reached certain stages of its development, so you’ll know the exact moment when your compost is ready to use.

Here you’ll find more information about thermometers, and the composting process in general, to help you find the best compost soil thermometer and get the most out of your compost:

Checking if Your Compost is Too Cold

You might think that everything is going well with your compost pile – you’ve prepared the heap, got loads of organic waste material on it, and are patiently waiting for that quality compost yield to come.

The problem is, without using a thermometer, you can’t really know what’s going on with your compost and if it’s working effectively.

The optimum temperature for a compost pile is between 55-72°C (131-161°F). If you don’t add any more organic matter, the compost can remain at this temperature for up to several weeks. This is ideal for efficient composting.

However, sometimes the compost pile might be colder than this, which can be checked using a thermometer.

If you’ve identified that your compost is not heating up, these steps should help you get it warm again:

  1. Compost can fail to heat up if the compost pile isn’t large enough. If your compost thermometer shows that the core of the compost it too cool, consider the size of your compost heap. Hot-compost piles need a minimum biomass of 3 m³ – this can be achieved in a composting area that is 1 x 1 x 1 m. The aerobic bacteria in the compost pile will get to work and heat up the contents, but, without enough surrounding biomass for insulation, this compost heat will get lost quickly.
  2. Another thing to consider after getting a low temperature reading on your compost thermometer is whether you are turning the heap frequently enough (or too frequently!). The heat is in the core of the heap, so it’s important to flip it regularly to make sure the ‘shell’ (outside) of the heap gets some time in the centre. Plus, turning the pile aerates it as well. This should be done approximately every 3 days.
  3. Your compost pile might be too dry, which will result in it being too cool to work properly. This might be something you can’t tell without a getting a ‘cold’ temperature reading from a compost thermometer. Moisture is needed to help microbes survive, and they’re what create the heat. Compost should feel damp, not dry, with a moisture level of 40-60%. You can add water to your compost heap if it’s too dry, but avoid adding too much. A balance needs to be found between the compost having access to enough oxygen and enough water (so you want to avoid filling all of the airways with water).

You can also use a compost thermometer to make sure your compost pile is correctly following through the different stages of composting. Which leads us onto the next section:

The Different Stages of Composting

It’s really important to know what stage of composting your compost pile is at. This can dictate what action you need to take with it, and also let you know when it’s ready to use.

These are the different stages:

Heating Up

If all of the correct conditions are met (see information above in “Checking if Your Compost is Too Cold”), compost should start warming up within a couple of days. Different microbes get to work at different temperatures, so at each heat stage different activity will be taking place in the pile.

Optimum Heat

When the pile reaches a temperature of 55-72°C, this is the optimum temperature and known as the ‘thermophilic stage’. Compost will stay at this temperature for a couple of days whilst the microbes get to work, then, when this ‘hot temperature’ bacteria dies off, the compost pile will start to cool.

Regularly checking the temperature of your compost will allow you to keep an eye on when it reaches its maximum temperature, and when the temperature starts to drop.

Turning the compost pile every three days whilst it’s in this ‘optimum heat’ phase should help it maintain this temperature for around 10 – 15 days. If, in this time, the temperature drops below 55°C or rises above 72°C, this is another indication that the heap should be turned.

Cooling Down

Eventually there comes a time when most the bacteria that works at the hottest temperature dies off completely, and the pile will cool down.

When it cools down enough, if there is more composting to be done, the bacteria which work at lower temperatures will come back and kick start the cycle again.

Identifying When Compost is ‘Ready’

When compost has gone through all of the above stages and is no longer producing heat, it’s likely ready to use. Finished compost has an ‘earthy’ ‘dirt’ smell, and there won’t be any of the original organic matter visible. The pile will generally be half the size that it started out as, and the ‘compost’ will be dark and crumbly.

Choosing a Well-Designed, Durable Thermometer

Compost thermometers are designed to be used in warm and moist environments, so key features to look for are durability and rust resistance.

The best compost thermometers have a stainless steel body; this is an ideal material for moist conditions as it’s rust resistant. Of course, a plastic compost thermometer won’t rust either, but it may get brittle or break when inserted into more compacted compost.

A common problem with compost thermometers is condensation getting into the dial. This can make it difficult to take a temperature reading. Some dials are hermetically sealed, meaning they’re airtight. The best compost thermometers will have hermetically-sealed dials and an ‘ingress protection’ rating of IP55 or more.

A rating of IP55 means the compost thermometer is sealed tightly enough to not allow dust in, and is also water resistant (it’s just not resistant to immersion in water). This helps prevent fogging.

Compost Thermometer Probe Length

The length of the probe is important, as you’ll need to take the temperature from as close to the middle of the pile as possible. While your measurements don’t need to be right at the centre, taking the temperature close to the surface of large piles won’t give an accurate reading of what’s really going on at the core.

A probe of around 50 cm long is suitable for large piles of compost; some thermometers have a probe of 40 cm or less, but it’s advisable to check the size of your compost pile before buying a smaller thermometer. A 50 cm or 40 cm probe is generally optimal for taking readings from the middle of the pile.

You may occasionally come across compost thermometers with a much shorter stem than this and wonder what they’re used for. Shorter stems, around 20 cm, can be used for checking temperatures in shallower worm composting trays. Other thermometers are too long to be useful in this context. Worms like compost temperature to be between 12 – 26°C, so there are different requirements compared to a hot compost pile.

Displayed Temperature Range

How the temperature is displayed on the compost thermometer can vary between models. Most thermometers measure in 1 or 2 degree increments and the best models will have a range of 0 – 100°C. Cheaper models may have a smaller temperature range.

Some of the best compost thermometers come with colour coded sections, so you can see whether the pile is ‘warm’, ‘active’ or ‘hot’. This makes the compost thermometer easy to read quickly, as you’ll be able to see at a glance where your compost pile is in its heat cycle.

You may have a preference when it comes to reading temperatures in Celsius or Fahrenheit. Some thermometers are exclusively in Celsius or Fahrenheit, whilst others display both units. If you’re looking at a compost thermometer which shows both Celsius and Fahrenheit, make sure it’s clear to read and understand. Some thermometers that display both still favour one unit over the other and can be hard to interpret quickly.

A Clear, Easy-Read Dial

Trying to find a dial that doesn’t mist up when in contact with humid compost can be difficult.

Some have an anti-fog coating which helps avoid fogging on the outside.

Condensation on the inside can also cause problems and make the dial hard to read. The best way to avoid this is by keeping the compost thermometer as dry as possible and not leaving it outside. Purchasing a compost thermometer with a ‘water resistance rating’ (e.g., IP55) should also reduce the amount of moisture that is able to creep in.

Dials which are ‘hermetically sealed’ are better at preventing condensation and water ingress. A hermetically sealed dial is designed to keep things completely airtight.

When it comes to the dial itself, a dial which is 50 mm in diameter is generally easy to read from a distance. If the numbers are too small, or of a lighter colour, they can be hard to read, so large numbers that contrast with the background colour are optimal.

Some thermometers have dials with coloured zones to quickly show whether the compost is ‘warm’, ‘active’ or ‘hot’. This makes an ideal compost thermometer for reading from a distance without needing to see specific numbers.

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Compost Thermometer FAQs

How do I use a compost thermometer?

Simply insert the thermometer into the compost bin or pile as far as it will go. Wait until the hand on the dial stops moving and make a note of the temperature. It is advisable to check the reading in several areas of the compost heap as there is not always a uniform temperature across the pile and you may occasionally find cold or hot zones.

How often should I turn my compost pile and what temperature should it be when I turn it?

Ideally, for a hot compost pile, once the temperature reaches between 55°C and 72°C (the ‘thermophilic stage’) you should turn it every three days. It should maintain this temperature for around two weeks. If the temperature drops below 55°C in this time, or goes above 72°C the pile should also be turned.

After this couple of weeks the temperature will drop and the process will start from the beginning. You will need to continually check the temperature of the compost pile until it starts to rise again.

How do I know when my compost is ready for use?

Quality compost that is ready to use looks dark and has a crumbly texture. It smells ‘earthy’ and has no residue of any of the original waste material that you fed to it.

Whilst finished compost can still retain a little heat, the pile won’t be particularly warm. The temperature of ‘ready’ compost will be approximately 21°C.

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Compost Thermometers Price Comparison

Every day DIY Garden scans thousands of products to help you find the cheapest prices. Not only do we want to help you find the best products through our in-depth testing, but we also want to help you find the best places to buy them too. We’re working hard to expand our network of retailers, and will be continually adding in new options.

The Cheapest Compost Thermometer Prices Found Today

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