Guide: How To Test Compost Quality At Home

Most gardeners will try their hand at making compost at some stage in their gardening career. It makes sense. You have all the trimmings and cuttings from your garden, and there is the kitchen waste you usually toss in the garbage. Some gardeners even have access to cow or horse manure. All of this can be used as compost instead of paying for compost from gardening shops and nurseries. In theory, this all seems simple, but a question that flummoxes many would-be compost makers is determining when the compost is ready for use and whether it is good quality compost. 

Test compost at home by observing the color, texture, moisture content, odor, and heat. You can also do a wood breaking test, compost-in-a-bag test, and a grow test. You can buy a pH testing kit to assess the pH of the compost. Compiling the compost correctly will help ensure good quality compost.

There are various ways to ensure that compost is mature and of good quality without sending it to a laboratory. Besides the compost assessment, it is essential to ensure you add the right ingredients to your compost. 

Good And Bad Compost.

Good compost consists of decomposed organic matter that contains nutrients for the soil. It smells earthy, has loose particles, and is reasonably dry. Bad compost contains toxic substances and pathogens. These harmful elements arise when the wrong substances are added to the compost. An example would be dog or cat feces. Compost must be allowed to mature in order for it to benefit plants. Immature compost will rob nitrogen from the soil and plants if you dig it into the ground before it is fully decomposed. The decomposition process requires nitrogen and soil. Immature compost will therefore utilize all the nitrogen and oxygen, leaving nothing available for the plants. 

Testing Compost Quality.

Commercially produced and sold compost is tested scientifically to evaluate elements in the compost. A sample of the compost goes to the laboratory and is analyzed for the following characteristics:

  1. pH – this refers to the acidity or alkalinity of the compost.
  2. Soluble salts – certain levels of salts are needed, but too much can cause the plant to die.
  3. Nutrients – 
  4. nitrogen, phosphorous, and potassium are the three most essential nutrients for plants.
  5. Moisture content
  6. Organic matter.
  7. Particle size.
  8. Maturity
  9. Stability 
  10. Inerts – These are non-biodegradable materials that have found their way into the compost.
  11. Trace metals
  12. Pathogens.

If you are interested in acquiring more knowledge about the scientific analysis of compost, click here.

Of course, gardeners have been making their own compost for years, and they have not had the compost tested in laboratories. In previous eras, when people lived closer to nature, many people had compost heaps in their backyards. It was regarded as a common task with no special knowledge needed.  It is possible to evaluate your compost quality at home and determine when it is ready to use.

Using Your Senses To Test Compost.

You can use your senses to help evaluate your compost. Before you dismiss this as a bunch of twaddle, it is worth considering that many scientific, medical, and veterinary professional manuals mention the importance of utilizing the senses when evaluating a problem. 

The Color Of Compost.

When you begin your compost pile, there will be many different colors in the mixture. You may have brown leaves, reds, or yellows from wilted flowers, green grass clippings, olive-brown horse manure, white eggshells, and many more. Mature compost will have blurred all those colors together during the process of decomposition. It should look a uniform brown to black color. If you see grey, beware it is more than likely mold that has developed because the compost was too wet. 

The Texture Of Compost.

Compost should look like dark, crumbly earth or soil. If you pick it up, it should fall easily in crumbs or particles from your hand. If you can see still see the individual elements of the compost, then the compost needs longer to mature. The exception to this is bits of bark or wood which should still be the same color as the rest of the compost but may show remnants of its original form.  

If there is a lot of fibrous material pieces, such as wood, in the compost, then the chances are that you need to allow the compost more time to decompose. It can also occur if the compost pile was too dry. You can take these pieces out by sieving the compost or picking it out by hand. Put the fibrous pieces in your new heap of compost if the rest of the compost seems mature. Alternatively, you can dampen the compost and allow it to mature for longer. 

The Moisture Content In Compost.

Feel the moisture content in your compost. If it is dripping wet or you can squeeze water out of the compost, then there is too much moisture. It would be best if you allowed it to dry out. This can be done by ensuring there is adequate drainage. You can also turn the compost regularly to enable it to dry out. Compost that feels slightly damp in your hand is acceptable. Generally, the more mature the compost, the drier it will feel.

The Smell Or Odour Of Compost.

Compost will always have some smell. If it is an offensive smell, then your compost has not decomposed enough, or something has gone wrong in the processing and management. The decomposition process releases nitrogen. If you smell a sharp stinging smell that burns your nose, then you are smelling ammonia. 

Ammonia is a gaseous form of nitrogen. If ammonia is present, it means that the compost has not altered or fixed the nitrogen into a state where it is contained in the solid elements of the compost. It is still in a gaseous form and cannot be used by plants. If you use a lot of old stable bedding or chicken manure, you will get a sharp ammonia smell until the decomposition process is complete. So, please don’t be shy; take a good whiff of your compost to assess its maturity.

The Heat Of Your Compost  

Take samples from different places in your compost heap. Try to get some from as far into the middle as possible as well as from different sides. Compost should feel cool to the touch. If there is any heat, then the decomposition process has not been completed. You will need to leave your compost to mature for longer. 

Other Home Tests For Compost.

In addition to using your senses to determine the maturity of your compost, some other more objective tests can give you information on the maturity and quality of your compost. These involve a little more effort but will provide you with some additional valuable information. 

The Wood Breaking Test.

When you are building your compost heap, add some untreated wood pieces. Wood pieces are one of the most difficult materials to break down due to the complex structure of the wood. Small pieces, such as wood shavings, will break down quicker, but larger pieces will take some time. Wood only starts to degrade once the compost heap has reached the high-temperature phase. If you think your compost is ready, fish out a few pieces of wood from the compost pile and examine it.  

If the wood is still light-colored, hard, and difficult to break, your compost is still in the early stages of decomposition.  It needs a much longer time period before it will be mature enough to use. The compost is probably only beginning the heating phase. Wood that has started to darken towards the edges and feels slightly bendable or pliable indicates that the compost is beginning to mature, but more decomposition is needed. If the wood is dark, moist, and is easily broken or crumbles under pressure, then the compost is mature enough to use. 

There can be some variation in this test, depending on the type of wood used. Softwoods such as pine will break down quicker than hardwoods, but the test is still worth doing as it gives some objectivity to the assessment of the compost. 

Grow Test For Compost Maturity And Quality.

This test takes some time, and you need to remember to water the test containers to ensure that the seeds have every chance to germinate. 

  1. Select eight to twelve containers. 
  2. Separate the containers into two groups. One group will be the control group, and one group will be the compost group. 
  3. Label each container as either compost or control. 
  4. Fill the control group containers with potting soil.
  5. Fill the compost containers with compost from various parts of the compost heap.
  6. Put six seeds into each container. Choose seeds that germinate quickly, such as bean or radish seeds. 
  7. Place one control and one compost in various spots around your nursery or garden. 
  8. Water the containers to maintain the right amount of moisture for seed germination.
  9. After seven to ten days, check the containers. Count the number of seeds that have germinated in each container. 
  10.  You can either compare these as a plain number or work it out as a percentage. 
  11.  If there are fewer seeds that have germinated from the compost than from the potting soil, then the compost is immature or of poor quality. If you get the same number of seedlings from the compost and the potting soil
  12. If your compost needed to mature further, then wait another three weeks before completing another test. 

It is essential to have the most beneficial light and temperatures to facilitate the germination of the seeds. It is not helpful to try and complete the test under conditions where the seeds would battle to germinate normally. 

Compost In A Bag Test

Select compost samples from various sites in the compost heap. It is vital to take the compost from multiple locations as it is possible for the center or sides to have different rates of decomposition. If the compost is not turned regularly, there will be different maturation rates in the different areas of the heap. 

Place each sample in a sealed bag and leave the bags for one week. Open the bags after a week and smell each bag of compost. If there is a foul smell from any of the bags, then you need to reassess your compost heap. It may need to be managed differently, or it may just need to have more time to mature.  

Measuring the pH Of compost.

Measuring the pH of compost is important as some plants do best with a more acidic pH and some with a slightly more alkaline environment. You can also track the process of decomposition by measuring the pH.  Various methods can be used to test pH. 

A soil testing pH kit can be purchased and used to measure the pH of the compost. Simply follow the manufacturer’s instructions. 

A pH strip can be used for compost that is moist but not wet enough to be considered mud. You can also take a sample of compost and put it into a container with distilled water. Let it percolate for five to ten minutes and then dip in the pH strip. Compare the color on the strip with the pH indicator colors on the side of the bottle or packaging. 

A calibrated pH meter is more expensive and can be used to grade a sample of compost in distilled water. There are various methods of treating the compost before measuring pH. If you would like to know more about pH in compost, click here.

Trouble-Shooting Compost.

If the compost has a bad odor, smelling either like refuse or ammonia, there is probably not enough air getting into the compost pile. Turn the pile to aerate it. Check to see if there is too much moisture, as this could also cause unpleasant odors. If the compost looks like mud, add more dry materials.  Too little moisture will result in compost that is not decomposing or is only decomposing on the outsides. The center of the heap will be dry or smelly. Add water while you turn the compost over. 

Sometimes the compost may be damp and smell acceptable, but there is not enough heat to cause decomposition. This is often the case where the nitrogen content is low. The remedy for this is to add nitrogen-rich materials, such as grass clippings, stable bedding, fresh manure, or blood meal. 

If your compost pile is only heating up and decomposing in the middle, then your pile may be too small. You need to add more materials, moisten them and turn the heap regularly. 


Compost is a natural phenomenon that gardeners use on a more intensive scale to provide natural fertilizers for their plants. Making your own compost can represent a sizeable financial saving, especially if you have a large garden. Some gardeners prefer to make their own compost so that they can be confident that all the elements are natural and beneficial. It is crucial that compost is well-matured before it is used. Immature compost will be detrimental to the soil and plants. 

Compost can be assessed using your senses to judge the color, texture, heat, moisture content, and odor. Objective testing can be done using the wood breaking test and the growing test. The pH or acidity levels of the compost can be tested using a pH soil test, pH strips, or a calibrated pH meter. 


Compost Fundamentals. Compost Needs.

Cornell Composting. Monitoring Compost pH.

Texas A&M Agrilife Extension. Composting.

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