Keeping your soil fertile is important no matter what plants you’re growing. Because of this, compost and humus are often incorporated to improve the soil. Since we’re not all agricultural experts, many people wonder what’s the difference between compost and humus and which is better.
Compost and humus are very similar, as humus is just highly-degraded compost with added horse manure. They are both used differently, and neither is superior to the other. If used right, both are beneficial for the garden.
It’s not that simple, though, as compost and humus have different characteristics and effects on the soil, despite being similar. Read on to learn about compost and humus, how to make them, and how to use them.
Compost is a mixture of organic materials that are added to the soil when we want to improve plant growth. It improves the physical, chemical, and biological properties of the soil.
The four crucial ingredients that ensure the efficiency of composting are:
To understand how to make good compost, we need to know how the four ingredients affect compost.
Carbon releases energy in the form of heat, which is necessary for the composting process. The bacteria in the compost use carbon as an energy source, and devouring carbon releases heat, as mentioned above.
Nitrogen is necessary for the bacteria to grow and reproduce, as they build protein from it. Because of this, nitrogen-rich ingredients are absolutely necessary for a compost pile. Too much nitrogen, however, ends up with an ammonia-smelling compost pile.
The air factor is important for energy production. Natural aeration is weakened by composting, as the pile’s porosity is reduced, so it’s necessary to aerate a pile manually.
Lastly, let’s not forget water – microbial activity is greater in water, so moisture levels need to range between 40 and 60%. More than 60% will present a problem with air, and less than 40% will slow down the bacteria too much.
How to make compost
Making your own compost is easy enough, and people have been doing it for centuries. In preparation, we’ll need the following items.
The greens provide the microorganisms with nitrogen, including wet materials, such as fresh grass, fruit waste, green hay, leaves, and weeds. Green means fresh, wet, and green plant stuff.
The brown materials are dry – dry leaves, straw, wood chips, nut shells, sawdust, etc. The keyword here is DRY (or brown!).
There are a few things that we shouldn’t compost, even though it might sound like we should. For example, don’t compost pet waste, meat, fish, and plants that died from disease, and pesticide-treated yard trimmings.
A compost pile is simple to create – we have to use about the same amount of browns and greens, while the size of the particles should be small but not shredded. It’s easier for microorganisms to digest smaller pieces of vegetation.
The pile size depends on our location, believe it or not. If our yard gets particularly windy, we can build a 4x4x4-foot pile. If not, a pile about one cubic yard in size should be large enough to become self-sustainable in most areas.
Regarding ratios, I usually aim for 1 part brown to 1 part green. I then add enough water to dampen the pile when I start it – and then I let the weather handle adding enough water from there on out, as long as there isn’t a smell test failure.
When I start the compost pile, if it’s large enough, I may add a little bit of barn lime (a handful every few layers) for good measure. I’ll add a bit of water with the lime, too.
With this method, I get a good amount of compost every season (3-4 months) and don’t even have to turn it. It also doesn’t have any smell. If it does smell, it’s because the ratio was wrong. Adding more browns (usually the ones that are not enough) fixes the smell problem, though I may throw another handful of lime on the pile for good measure.
Humus is an organic layer of soil, easily recognized by its dark color, that develops with the composition of plant and animal matter.
In a way, humus undergoes a similar decomposition process to compost, but it takes longer, and humus becomes very finely decomposed.
We can recognize humus by its dark color and spongy appearance, making it unique.
We’ll go into the difference between humus and compost in detail later.
How to make humus fertilizer
Since humus is just a very potent layer of soil, basing its effectiveness on the same process as compost does, all we have to do to create humus is create compost first.
The slight difference in ingredients is that humus needs some manure added to the deteriorating plants, but aside from that, the ingredients are the same. No other animal droppings should be added – only horse manure.
After they decompose, which can take weeks or months, depending on how much humus we’re making, we can integrate them as the top layer of soil.
We’ll know that the compost has become humus once it becomes black and spongy.
Why Is Humus an Effective Fertilizer?
Many people do not know that humus has a nutrient-storing capacity. It stores nutrients in the soil, which means that they cannot be destroyed or washed out by rain and irrigation. The nutrients are always available to plants.
Humus drastically increases the chemical and physical fertility of the soil while it’s also capable of suppressing some types of diseases (source). It also improves moisture retention, and it feeds the microorganisms that are beneficial for plants.
Since humus retains so much water, it increases the soil’s drought tolerance. It can hold up to 90% of its own weight in moisture (source).
This is, in a nutshell, why humus is a great addition to any garden.
The easiest way to differentiate compost and humus is by the way they are used. Compost is often used as a fertilizer – spread and plowed into the soil, while humus is integrated as a layer of soil – this layer is usually thicker and more compact than spread fertilizer.
The distinction between compost and humus is difficult because they’re similar. After all, humus is compost with added manure that’s decomposed into a spongy black matter and integrated into the soil.
According to experts, the difference between humus and compost is often irrelevant, and it’s only important semantically. Even on that level, there are different definitions.
Natural compost (the kind not created by man but by natural composting in the wild) is sometimes called humus.
So, to sum up – the two clearest differences are:
- Compost doesn’t have to be as decomposed as humus does to be used.
- Humus is (most often) integrated as a thick layer of topsoil, while compost is spread thinly as a fertilizer or even used as a landfill cover.
There are also differences in effects. For example, since compost is spread as a fertilizer, it doesn’t have the same water retention abilities as humus (not to be confused with the most delicious and edible hummus).
Humus is finely decomposed compost, and while we can spread it around thinly like a fertilizer, it’s simply not intended for that, and we’re wasting its potential. If possible, always spread humus as a top layer of soil. Use mulch or fertilizer on top of the layer of humus.
To spread fertilizer around the garden and help the plants, use humus instead of compost. However, it can be a waste of humus.
Compost is used for many different things, but it’s never used as a layer of soil – that’s what humus is for. Humus, on the other hand, is used precisely for that.
Organic humus and compost are technically not the same. When it comes to composition, the biggest difference between humus and compost is manure. Compost uses the same materials as humus but doesn’t need horse manure, while humus requires horse manure as an ingredient.
If we want to make humus, we’ll have to add horse manure.
Also, we can spread compost after a few weeks of decomposing – humus isn’t ready until it’s spongy and black!
Integrate humus into the soil by adding 2-4 inches of humus over the topsoil and then digging it in with a hoe into the top layer of soil. We do not need more than 4 inches, but it is important that humus stays near the top of the soil.
Humus needs to be very congested – we can’t spread it thinly. This is why it’s most effective in garden beds – it’s easier to spread it (we’ll lose count of how much we used and where if we spread compost over an open area).
Humus is especially useful with sandy soil, which drains and dries out quickly, and clay soil, which retains too much water.
Compost is used differently – it’s spread around like a fertilizer and incorporated into the soil. We don’t have to spread it as thickly as we do with humus, but we’ll have to dig it in with a hoe.
Key Takeaways and Next Steps
As we can see, humus is a highly-effective derivative of compost, but the two are used differently. Ideally, if we have enough time on our hands, we should create both compost and humus, as the garden will certainly benefit.
If not, know that we can always buy high-grade compost and humus and that integrating them into the soil will improve its quality.
Here are some other ideas to add to compost if you want to make your own:
And if you’ve got access to alpaca manure, it’s amazing. Make sure you know how to use it in your composting, and read our complete guide here: How to Fertilize with Alpaca Poop: The Complete Guide.
Learning from your own experience is important, but learning from others is also smart. These are the sources used in this article and our research to be more informed as homesteaders.
- “Composting at Home.” US EPA, 7 July 2022, www.epa.gov/recycle/composting-home.
- “EFFECT OF ORGANIC CARBON ON AVAILABLE WATER IN SOIL : Soil Science.” LWW, journals.lww.com/soilsci/Abstract/2005/02000/Effect_of_Organic_Carbon_on_Available_Water_in.2.aspx. Accessed 3 Nov. 2022.
- Hoitink, H. A. J., and P. C. Fahy. “Basis for the Control of Soilborne Plant Pathogens With Composts.” Annual Review of Phytopathology, vol. 24, no. 1, Annual Reviews, Sept. 1986, pp. 93–114. https://doi.org/10.1146/annurev.py.24.090186.000521.
- The Editors of Encyclopaedia Britannica. “Humus | Soil Component.” Encyclopedia Britannica, 19 Apr. 2020, www.britannica.com/science/humus-soil-component.
- The Science of Composting – Composting for the Homeowner – University of Illinois Extension. web.archive.org/web/20160217221013/http://web.extension.illinois.edu/homecompost/science.cfm. Accessed 3 Nov. 2022.