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What Is Humus? What Are Its Uses For Gardening

by Max on Sun, 09/23/2018 - 01:26

The word humus comes from the Latin word humus, which means ground. The definition of humus can vary slightly depending on which field of science is addressed.

When it comes to soil science, humus means the part of soil mater that does not have the structure of plants and animals. It functions to affect the density of soil and leads to the ability to retain water and nutrients.

In agriculture, humus can refer to the natural compost that comes from forests and other natural sources. These are used to improve the condition of the soil. Humus can also refer to the layer of the soil that has organic matter.

Although not exactly the same, these two viewpoints on humus are connected. In any case, the use of humus has been around for centuries. Its use was first documented in the 18th century, although it is possible that it was used for much longer. Today, humus is still used for the healthy growth of plants.
Here in this article, we examine humus, its composition, and its uses for gardening.

What is Humus?

Humus is an organic, non-living matter that exists in the top layers of soil. It is the byproduct of the decomposition of plants and animal materials.

Humus exists in the topsoil layers
Humus exists in the topsoil layers - Accumulated from here and here

Humus refers to the dark substance, ranging from brown to black, that remains when the majority of the organic waste has decomposed. Ground-dwelling animals like earthworms, work to incorporate the humus with the soil to enrich it further.
The benefits of humus emerge when it decomposes, which would then make it possible for plants to use them. Humus is often used by to fertilize the soil.

Aside from adding nutrients, it also loosens the texture of the soil. With a freer texture, air and water can more easily penetrate, and oxygen can reach the plant’s root system faster.

Some experts also believe it has the ability to prevent plants from getting hit by the disease.

As part of the life cycle, plants shed leaves, branches, and other plant parts. When it falls to the ground, it creates a layer on the ground called leaf litter. Animals, too, die. The carcass also comes in contact with the ground and becomes part of the soil.

All these materials will undergo a process of decomposition. The original form breaks down and returns to the most basic chemical components.

These substances are also the same nutrients needed by soil-dependent life forms like plants.
Aside from the natural process that creates the humus, it can also be made through composting. People can collect organic waste material such as discarded food or fruit and vegetable peelings and then turn it into humus.

The main component of soil is humus, making up more than half its content. It should be noted that humic substances, which are the parts that make up humus are mostly heterogeneous and relatively stable. Thus, they can provide structural stability to the soil.

The humus found in soils are usually centuries-old. Instead of disintegrating into carbon dioxide, the organic matter was prevented from complete disintegration by the microbes and their enzyme production. If humus is unprotected, then it will decompose in about a decade and be transformed into a less stable form.

When humus is stable, it does not provide a lot of nutrients for plants but instead improves the texture of the soil. Stable humus occurs when there is slow oxidation of the soil carbon when materials like charcoal are incorporated into the topsoil. An example of such an occurrence is the formation of the rich soil of the Amazon.

What is Humus Made of?

Humus is made from the breakdown of living things. Thus, it is mainly composed of carbon. The other components are nitrogen, phosphorus, and sulfur.

When an organism decomposes, the humus is separated from the other components of the organic material like protein and fat. Most of the small molecules that do not turn into humus decompose rapidly because of microorganisms.

But, soil humus takes its time to decompose, assuming that the conditions are all normal. In fact, the process of creating humus – called humification – can take hundreds of years.

Its composition also leads to the major classifications of humus, which are mor, mull, and moder. Aside from the type of organisms that created humus, another determining factor of classification is how incorporated it is to the soil.

The first type of humus is the mor, which is also known as the raw humus condition. It occurs when the soil has very few micro-organisms or animals in it. Examples of these animals are earthworms or beetles. Fungi are also considered as part of this ecosystem.

These animals aid the decomposition of the organic matter found under the soil. The soil is layered with surface litter and underneath it usually lies the humus layer. Underneath the humus is the soil.

If the humus layer does not have enough animals-life around it, the mor soil becomes more acidic than usual. This usually occurs in coniferous forests or places where there are high altitudes and cold weather.

The second type of humus is called the mull humus. This usually occurs in hardwood forests or grassland where the weather is warm and humid. There are a lot of bacteria, insects, and earthworms to aerate the soil. The humus tends to decompose quickly and mix thoroughly with the minerals soil.

Mull humus we characterized as alkaline or having a high pH level.

Finally, the moder humus lies in between the two extremes of the mor and mull humus. Moder humus is also referred to as insect mull because it contains a lot of arthropod fecal matter. These materials tend to bind the plant and mineral particles to form a netlike formation.

The moder humus has more organic material than the mull, but it is unable to mix well with the mineral substances in the soil.

Pros and Cons of Humus


The big-picture benefit of humus is mainly related to the enrichment of soil to result in healthier plants.

The humus improves the structure of soil material by binding the particles together. This is called tilth. The effect of humus is particularly noticeable in soil with high concentrations of sand and clay.

The humus acts like a sponge because of its organic nature and soaks up water and nutrients. It also helps minimize the erosion of sand-heavy soil and water runoff.

Fortunately, humus is already commercially available. One of the most practical advantages of using it is that it is easily accessible through online shops or garden stores.


However, humus does have its shortcomings. Compared to other fertilizers, such as manure, humus is low in nutrients. It can increase its nutritional value, but it will take several years because it relies on microbes and earthworms to generate the added nutrients.

It can also be difficult to tell the content of the humus and whether it is the best fertilizer to use. Aside from its origins, the composting method undergone by the humus is also a factor in its nutritional content.

If it were produced by cold composting or slow composting, it would not give off enough heat to kill the pathogens and invasive material such as weed seeds. On the other hand, hot composting occurs when there is a nitrogen source like manure. This process sterilizes the humus, but it has fewer nutrients.

How to Use Humus in the Garden

A heap of soil and humus
A heap of soil and humus

Humus can be added to the different types of soil to make it more robust. The humus contains plenty of plant nutrients as well as minerals. It usually also houses bacteria and other micro-organisms that are needed for plants to grow healthy and strong.
Here are the steps on how to use humus in the garden.

Determine how much humus is needed

The general ratio of humus to the soil is about one cubic foot of humus is used in 25 square feet of soil. A cubic foot is about one full wheelbarrow. Adding more this standard amount will not affect the plants negatively.
Mix the soil before adding the humus.

Loosen the soil that the humus will be mixed into. The idea is to eliminate the clumps of soil to aerate them. The mixing should occur up to a depth of about a foot or about seven inches, at a minimum.

Incorporate the humus with the soil

In cases where the humus already as clay nutrients, it can be applied to the soil without further preparation. A shovel can be used to spread out the humus in an even layer. It is recommended to work in small areas so that the nutrients are not lost from the exposure to the elements, like unexpected rain.

Once the humus has been applied, mix the soil a second time. The humus can be applied twice, one day apart, to increase its effectivity.

Using humus on rooting beds

Humus can be used for potted soil or rooting beds. In the case of the later, fill the bed with a layer of dried leaves and then top it with humus. Add a layer of sand, of about two to four inches. This sand layer will help trap the moisture in.

This set-up is ideal to grow new plants because the roots do not encounter obstacles when they spread out. The sand also lessens the loss of nutrients, from runoff. Finally, the loose texture of the humus soil makes it easy to uproot the seedlings so they can be placed in more permanent locations.

Frequency of Treatment

Poor soil needs to have humus applied to it fairly regularly. It is ideal to test the soil for acidity before applying any treatment. The pH level of the soil should fall within the range of 6.2 to 7. If the soil is too acidic, adding gypsum or lime is necessary before adding in the humus. On the other hand, low pH levels could require the addition of a water and ammonia mixture.

Adding humus to unbalanced pH soil is not harmful, but the soil will not be as conducive to plant growth because the underlying issues were not treated.

Humus vs. Compost

A compost bin in the garden
A compost bin in the garden

Compost is another term that is often used in gardening or farming terminology. It refers to a mass of organic material that is undergoing decomposition. It is usually made from food waste, leaves, or grass clippings.

When composting, it is essential to turn the pile of materials regularly to mix the decomposed and decomposing materials together evenly. This helps speed up the composting process. When the process is done, the finished compost looks like soil. It does not contain any identifiable organic matter.

Compost is used in gardening to make the structure of the soil better. The looser soil allows air to penetrate the soil and increases its ability to hold water. Compost material also leads to better drainage and encourages the bacterial activities in soil.

The compost also functions as a fertilizer. As a result, the plants can absorb more nutrients.

There is another benefit to adding compost to plants. It can help suppress the growth of weeds and lock in the moisture.
To say that compost is finished decomposing is a loose interpretation. Compost still has a lot of decomposition activity at the microscopic level. The main difference between compost and humus is that compost contains a small amount of humus.

It can take years for compost to decompose to reach the humus stage. Once the decomposition is fully complete, then the compost turns into humus.


At first glance, humus seems like a straightforward material especially in relation to gardening. But the greater details reveal that it is much more complex.

With the breakdown of what humus is and its advantages and drawbacks, you can hopefully, decide how to utilize this substance. Do you think humus is worth the effort? Please let us know your thoughts. We would love to hear from you. If you found this article useful, please share it with others to spread the information on what humus is.

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