Difference between Humus and Compost???

chueh(7B)September 17, 2011

Can anyone tell me the difference between humus and compost. I always see "Humus" written on landscape trucks but not compost. Is compost what we call when we make it at home, where as humus is the same thing but commercially sold at stores?


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The following I found by Googling 'Humus'; one hit directed me back to Gardenweb. I did not find the same when searching (this forum) and viewing the Soil FAQs. ???
Anyway, here is part of the post.

Organic matter - stuff that came from biological sources (should be biological matter. Diamonds and graphite don't decompose!) This includes humus, mature compost, immature compost, freshly cut plants, live plants, etc.

Humus - (soil science) that portion of the soil that has fully broken down and is thus stable. This stability is important because it allows you to remove it from consideration in a lot of investigations, and this is why soil sciences define it this way. This, incidentally, is also why its constituents have not been subjected to rigorous scientific investigation. It is not that it is somehow mysterious or has magical properties that elude investigation, it is just that it is only recently that anyone has really bothered to think about applying modern analytical techniques to this fraction of the soil. Contrary to common belief, a large number of its constituents ARE known. Their relative proportions vary from implementation to implementation, however, and thus no simple answer is really forthcoming as to "what humus is," as it is a dynamic mix of substances. humus - (colloquially) The organic portion of the soil (you can see how this definition has use for the gardener, but is too impercise for much usefulness in an investigation of soil properties.)

Compost - organic matter in a purposeful state of partial decomposition. The purposeful part is important. Dead stuff on the ground is NOT compost, just decaying orgainc matter. It is the controlled, or semi-controlled conditions that make it compost.

    Bookmark   September 17, 2011 at 5:03PM
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dogwind(Z8a TX)

Robertz has got it. I think of humus as fully decomposed compost. As robertz stated, humus is stable, and will not break down anymore. Compost is not.

    Bookmark   September 17, 2011 at 6:03PM
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I love hummus... Yummmmm ;-)

Hummus Recipe

A chick-pea cream with garlic, Hummus, Oumos, or Humus
A delicious and healthy mediteranean recipe
Hummus is a cream of chick peas with garlic, lemon and olive oil, from Lebanon.


Compote Recipe:
is a dessert originating from 17th century France made of whole or pieces of fruit in sugar syrup

    Bookmark   September 17, 2011 at 6:42PM
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LOL at Jon's post!!!!

Thank you all for the replies. Robert's reply is super helpful. One more question though:

In gardening, what difference effect would humus and compost make for plants? The stabler the compost, the better???


    Bookmark   September 17, 2011 at 8:23PM
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'K, keep in mind I am not a soil guy, never had any training or education in soil science or any of that stuff so what I am saying is gut feeling and intuition.

It's not just having the organic matter in the soil, it's the digestion of that organic matter by the soil organisms that provides the nutrients to the plants. It's the actual breaking down of all the components that gives the plants what they want/need. We want the organics to break down continuously for the plants. We want that stuff to be digested. Now having said that, there is a point when having too much raw organic matter can lead to problems so heaping piles and piles of material can be detrimental short term and I stress 'short term'. The very rapid digestion can lead to all sorts of toxicity to a lot of plants. It can also rob the soil of oxygen which is also critical to plant survival. Over time, nature will deal with an overabundance of material and eventually get back to a more stable environment for plant survival. The volume of that material, and the environmental conditions it is in, will determine just how long it will take.

Humus is the 'stuff' that is left after all the easier digestion has taken place. Sure it has value, great value, because it's not only the ability to release nutrients but all the other things that are equally important in a good growing environment.

This is what active composting is all about, getting over the more toxic stage to a point where the material can be more safely used. This is also why we don't necessarily have to compost anything, smaller amounts of raw material can be processed within the soil without detrimental effects. The poison is in the dose so to speak.

You ask which is better? Well, they both have a role to play and ideally, both are beneficial for different reasons.

Clear as mud right?


    Bookmark   September 17, 2011 at 11:27PM
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Quickly and easily humus is the undigested part of compost, or any other organic matter, left in the soil.
Many people misuse the term, as the lettering on that truck indicates.

    Bookmark   September 18, 2011 at 7:14AM
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bluegoat_gw(Zone 3b)

This might be helpful. Remember, it has been translated.

Here is a link that might be useful: Soil Humic Substances

    Bookmark   September 19, 2011 at 11:36AM
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This discussion is excellent. It has really helped me clarify the definitions. Am I correct in saying:
Compost involves the process of decomposition which provides nutrition for plants. Humus is fully decomposed, inert, and provides soil structure and tilth.
I believe peat falls into the latter category.

    Bookmark   September 19, 2011 at 12:30PM
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While the scientists try to make things very complicated, and describing Soil Organic Matter can be, the KISS principle is good for the rest of us to remember.
Humus is the undigested organic matter in the soil.

    Bookmark   September 20, 2011 at 7:49AM
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While the scientists try to make things very complicated

The point isn't to make things complicated or simple. The point is to gain a better understanding over time. If you find science to be complicated and/or confusing, it's not the fault of any scientist for crying out loud. Just stay out of the deep end of the pool if it makes you uncomfortable.
Anyway, you've got it bass-ackwards. Re-read Lloyd's post.

    Bookmark   September 20, 2011 at 9:40AM
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Soil (and all its components) is complicated, that is why it is still being studied.

Wikipedia has a not bad article that even I (mostly) understood.


    Bookmark   September 20, 2011 at 11:28AM
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