How To Test Your Compost To Know if It’s Ready

While the composting process can be rewarding and simple once you get used to it, the process can take some time to learn. One of the most difficult parts of composting is knowing when your pile is ready. This is also one of the most important, as an immature pile can pose a danger to your plants and soil. 

The best way to test your compost to know if it is ready is to observe the physical characteristics of the pile. A ready compost pile should look brown, smell earthy, and be the same consistency throughout. 

Let’s get into more detail about how to know if your compost is ready and when you should consider letting it go longer. 

1. Finished Compost Should Be Deep Brown

One of the fastest and easiest ways of testing the readiness of your compost is to check the color. The pile should be a deep brown color all the way through, making it look uniform. Once the pile is ready, you will no longer be able to distinguish individual materials in a pile.

If you turn your pile and notice an apple core or the rind of a watermelon, this is indicative of unfinished compost. When the composting process is complete, these materials will be dark brown and crumbly, matching the color and consistency of the rest of the pile. 

However, If your compost pile mostly consists of brown materials, such as tree bark and dried leaves, then it may be difficult to determine when it is ready simply based on the color. In this case, you will want to look for a uniform dark brown all the way through the pile. 

You can also refer to the other signs discussed further below.

2. Your Compost Pile Should Smell Earthy

Another way that some experienced composters recognize the pile’s readiness is by smell. A completed compost pile will smell earthy and ready to return to the soil. You may notice during the composting process that the smell of your pile changes. This is completely normal and will depend on the materials you put in it. 

One smell that concerns a lot of people not as familiar with the composting process is the sour smell the pile can sometimes get. A little bit of a sour smell is normal, but the pile smelling strongly of ammonia or a similar sour scent can mean that you have too few brown materials.

Ensuring you have enough brown material will help the compost pile smell less sour and work better overall. However, some sour smell is normal for composting. As the microorganisms are feeding on the materials in the compost, they can excrete a sour smell that can sometimes make you think something is wrong. 

In the case of a slight, not overpowering sour smell, this is just the microorganisms feeding and doing their job to break down the material. You can use that smell as a reference to easily tell when a composting pile is ready. Once that slightly sour smell goes away and an earthy smell replaces it, your pile is ready to use. 

3. Consistency Is Key

Consistency is one of the most important parts of determining that your compost pile is ready to use. One of the main things to look for in a ready-to-use compost pile is that the materials you initially put in have broken down to an earthy, dirt-like consistency. If you still see large chunks of materials in your compost, you may need to leave the pile to process some more.

One exception to this rule is seeing things like branches and sticks poking out of your pile. Sticks and branches take a long time to compost, even when you place the pile under suitable conditions. 

If your compost pile is already brown and crumbly, remove the visible branches and sticks and use the compost as a soil amendment. Place the sticks or branches on the next pile and allow them to break down. Ideally, you should cut them up into smaller pieces to speed up their composting process.

Remember, you should not do this with other materials that don’t take as long to compost. The best compost pile is one that you allow to completely finish rather than removing stubborn materials, but you can make exceptions for some things. 

4. The Compost Doesn’t Heat up When Turned

Suppose the microorganisms are still actively decomposing organic matter. In that case, you will notice your compost pile temperatures soar once you turn it. So one good indication that your compost is ready is when the temperature remains the same after turning your pile a few times.

When the materials in your compost pile have been completely broken down, the microorganisms have little to nothing left to feed on. This reduced biochemical reaction will keep the temperature of your pile stable.

Typically, a compost pile actively undergoing decomposition has temperatures ranging from 130 – 170 °F (54.4 – 76.7 °C). Higher temperatures can result from chemical reactions in a pile, which can be counterproductive because they can kill off good microbes.

That’s why it’s necessary to turn the compost regularly to release some of this heat and to spread it throughout the pile. It can also provide the microorganisms with easier access to organic materials that are yet to be decomposed.

Ensuring that the pile reaches and maintains a steady temperature will not only ensure that the composting process is successful and fast, but it also ensures that any weeds that have made their way into the pile completely die.

One simple way of determining that your compost pile is ready is to ensure that it is hot all the way through and that you allow the pile to maintain that temperature for as long as it needs. As you are mixing the compost pile and notice that it is no longer heating up as you move it, then it is ready to go. 

5. The Finished Compost Should Be Lighter

Another way to test whether or not your compost pile is ready is by observing the size of the pile. As the materials begin to decompose, they will crumble.

This causes your pile to significantly shrink in size compared to when it started. In fact, you can expect your compost pile to shrink about 70 to 80% depending on what is in it, according to the University of Missouri.

Because the composting process involves microorganisms digesting and breaking down these materials, the pile you end up with is going to be a lot smaller than the original pile. This is normal and a good sign that the composting process is complete and successful. 

This reduction in size is significant enough for anyone to notice and can indicate that the pile is ready to use. Noticing chunks of whole materials still in a pile is indicative that it is not ready, and a uniform compost pile should have small, dark brown crumbs. 

Each of these tests combined will certainly help you determine the readiness of your compost pile. In fact, a healthy compost pile should show each of these signs before you use it.

The size reduction of the compost pile will happen naturally as time progresses. So, it can be difficult to test if the pile is ready just by using this method alone. 

So, it is important to consider this observation with the others to determine the readiness of the pile. However, there is no doubt that over time as you become more experienced with composting, you will be able to recognize the readiness of the compost pile by just the size. Like everything else, it just takes time to develop that skill. 

Final Thoughts

You can tell if your compost is ready based on the following observations:

  • Deep brown in color
  • Has an earthy smell
  • Consistent texture
  • Does not heat up when turned
  • Significantly reduced in weight

The importance of having a completely composted pile can not be understated. Adding unfinished compost to your garden can spread unwanted weed seeds that can compete with your plants for nutrients and water.

So, always make sure your compost pile is ready to use before ending the process. Otherwise, you may end up with a pile that does more harm than good.

You could also check out my beginner’s guide on how to compost with and without a bin here: How to Compost With and Without a Bin (Ultimate Guide)

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.