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What Is Humus Soil?

Humus may be brown or black, and is lightweight and textured.
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  • Written By: J.S. Metzker Erdemir
  • Edited By: W. Everett
  • Last Modified Date: 26 November 2014
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Humus soil is soil made up of decayed organic material. Popularly, it refers to soil that is light in texture, dark brown or black in color, and sweet-smelling. It is considered the richest soil and is usually described as the ideal soil type. Most soils are a combination of the soil types, and tend have either more clay or more sand, with varying amounts of humus.

In terms of chemistry, humus is made up of completely decomposed plant and animal material. The material is broken down to its elemental form, and it is largely composed of carbon, hydrogen, oxygen, and a small amount of nitrogen. Humus does not contain active bacteria or microbiotic life, which makes it a stable substance because it will not decompose any further.

With regular cultivation, including the addition of soil amendments such as minerals to balance pH and fertilizers made of organic materials, the humus content of soil gradually increases over time. Although gardening stores sell bags of material labeled as “humus,” it is not really possible to create or harvest the pure substance. In nature, it is generally a combination of materials at various stages of decomposition. Pure humus soil contributes to the soil's overall quality. It is an integral part of healthy soil structure, which also includes minerals from sand or clay and organic matter that is still decomposing.

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Colloquially, humus can refer to any organic soil matter. It is often confused with compost, since the two can look alike. Finished compost should bear little to no resemblance to the original material that went into it and, like humus, compost has a light texture, dark color, and sweet-scent. The difference between compost and humus is that compost is still undergoing decomposition, and it contains live bacteria and other nutrients that directly contribute to plant growth.

Almost no soil is completely sand, clay, or humus. Sandy soil is generally poor in nutrients, and cannot hold water well, so it may not be able to hold up shallow-rooted plants. Clay soil is generally richer in nutrients, but water cannot drain from it and plants' roots often cannot penetrate it. Humus has the ability to hold moisture, which is why it improves sandy soil. At the same time, its light texture allows moisture to drain and oxygen to circulate, which is how it improves clay soil.

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Izzy78
Post 8

I always wondered what the importance of humus in soil was. I guess now I know. In some stores I have seen little soil sample kits that will tell you how good your soil is. Do these measure humus somehow, since it sounds like it is directly related to productivity?

I was also wondering why humus would differ between different locations. I now know it is what is responsible for making soil black. I used to live in Indiana and the soil was pretty dark and grew things really well. Eventually, I moved to the south, and here when you till up the soil it is very orange or red, which I think is clay. Why do these two places have different types of soil?

matthewc23
Post 7

@Emilski - Like the article also talks about, you shouldn't be fooled by bags at the garden center label as humus, since it can't be created at an industrial scale. It takes thousands of years for humus to form naturally.

Humus you find at the store to put on your plants is more correctly compost, which is decomposed organic matter, which still does have plenty of nutrients for plants as well as having a high water holding capacity.

Does anyone here know how much humus is typically found in most soils? I am assuming it varies depending on location, but what would an average soil be?

JimmyT
Post 6

@Emilski - Those are very good questions. First off, humus is pronounced with a long "u" at the beginning as opposed to the short "u" in hummus.

The article says that humus doesn't have any active bacteria in it, with active being the choice word. Like you alluded to, you would never find bacteria not located in certain parts of the soil. By definition, though, humus doesn't have anything left in it to be decomposed, it is at its most basic form, so the bacteria would have nothing to do.

While humus doesn't have any nutritional value in and of itself, it is still extremely important to have a lot of it in soil. Its molecules are very spacious, which allows it to bond with several soil minerals that plants do need. Also, those spacious molecules help hold water and add air pockets to the soil, and both of those things are critical to good plant growth.

Emilski
Post 5

First off, I have seen this word a lot, but I have never known for sure how to pronounce it. Is it pronounced like hummus the food, or is it different?

The article mentions that humus doesn't have any bacteria in it, but it is mixed in with the rest of the soil. I always thought that bacteria were all over the soil decomposing different organic matter. Also, it says that there are no nutrients in humus, so what would be the point of ever wanting to have it in your soil and putting it in your garden or flower beds?

wavy58
Post 4

I have noticed that when I leave my dead plants in a pile all winter, by spring, they have decomposed into humus. I go into my garden after the frost has killed everything, and I yank up the stalks, dead leaves, and tall, dead grass that has grown up around them.

I layer the dead material pretty thick around the garden. Through all of the snow, rain, and sun during fall and winter, the stuff makes humus rich soil beneath the layers.

In the spring, I rake away any material that has not decomposed. This reveals a deep, fluffy soil ideal for growing food.

lighth0se33
Post 3

@StarJo – Humus is great for controlling weeds. Nothing but ground cloth can totally stop them from invading a garden, but humus can help, especially if you add it after doing a bit of landscaping.

I always take a hoe and remove the top layer of grass and weeds from the area that I'm about to cultivate. After I have stripped it bare of everything but the soil, I add a bag or two of humus.

If I'm sowing seed, I will add the humus first. If I'm planting something already in bloom, I will plant it first and then add it around the plant. I mound up the soil around its base and cover it with humus.

The thicker the layer you add on top of the soil, the longer it will be before you have to weed the garden. I keep adding more throughout the summer, because the rain can wash some of it away.

Oceana
Post 2

I have a raised flower bed that I fill with potting soil. Last year, I used humus that I bought from a garden center instead, and my plants seemed to flourish more.

The humus is so rich and soft. It smells like the earth after a rain. I love having it in my yard.

It is so dark that it provides a great contrast to the brightly colored blooms that I grow. I have petunias that creep along the ground, and they look wonderful up against the black humus.

I have several rosebushes planted in the middle of the bed. I have not had much luck with growing healthy roses in the past, but since I used the humus, that has changed. I have some of the biggest, healthiest bushes around.

StarJo
Post 1

Every fall, I try to make humus soil in my flower beds. I pile on a couple of layers of pine needles and leaves, and I let them decompose until late spring, when the seedlings underneath are ready to emerge.

When I pull back the top layer of pine needles, the soil underneath is so dark, soft, and rich. I like to make humus on top of the ground over my tulip and hyacinth bulbs. I figure that if the soil is rich above them, when it rains, the nutrients will seep into the earth and reach the bulbs.

It seems to be working, because my tulips have been re-blooming for years. Humus also helps keep grass and weed growth to a minimum, so I don't have to work as yard the following season.

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