Compost vs. Humus: Why Is Humus Important In The Garden
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I like myth debunking as much as I like gardening. Myths are kind of like plants in a way, they keep growing if you feed it. One myth that we need to stop feeding or circulating is the one where we declare that compost is humus. No. Just no. Stop.
The terms ‘compost’ and ‘humus’ cannot be used interchangeably. So “what is the difference between humus and compost” and “how is humus used in gardens,” you ask? Read on to get the dirt about compost vs. humus. And, just in case you are wondering why we are comparing compost to the delicacy in your kitchen right now, I also want to take a moment to clarify that humus is not the same as hummus. Trust me. Humus just isn’t as tasty.
Difference between Humus and Compost
Compost is the black dirt, or “black gold” as we like to call it, created from the decomposition of the organic matter that we contribute, whether that be leftover food or yard waste. Compost is considered “finished” when we are left with the semblance of a rich organic soil where our individual contributions are no longer distinguishable. And, nice catch, I put “finished” in quotes for a reason.
If we want to be technical, it really isn’t finished, as it’s not completely decomposed. A lot of microscopic action will still be taking place as the bugs, bacteria, fungi, and microbes that we really don’t like to acknowledge are there still have a lot of material in that “black gold” to feast upon and break down.
So basically, the finished compost we put in our gardens really only contains a very small percentage of humus. Compost literally takes years to fully decompose into a humus state. When the compost is fully decomposed it will then be 100% humus.
What is Humus Made of?
As the little critters continue their dinner party, they break things down on a molecular level, slowly releasing nutrients into the soil for plant uptake. Humus is what’s left over at the conclusion of the dinner feast, which is when all the usable chemicals in the organic matter have been extracted by the microorganisms.
Humus is essentially a dark, organic, mostly carbon-based spongy substance in the soil that has a shelf life of hundreds of years or more. So to recap the whole compost vs. humus debacle, while humus can be created through the composting process (albeit very, very slowly), compost is not humus until it is decomposed down to dark organic material that can no longer be broken down.
Why is Humus Important?
How is humus used in gardens and why is humus important? As I mentioned earlier, humus is spongy in nature. This is significant because this attribute enables humus to hold up to 90% of its weight in water, meaning soil laden in humus will be able to retain moisture better and be more drought resistant.
The humus sponge also latches onto and safeguards nutrients that plants require, such as calcium, magnesium and phosphorus. Plants can siphon these much needed nutrients from the humus through their roots.
Humus gives soil a much desired crumbly texture and improves soil structure by making the soil looser, allowing for easier flow of air and water. These are just a few great reasons on why humus is important to your garden.
Humus vs. Compost
Gardening terms can be confusing, mainly because gardeners tend to use the terms in varying ways. Compost and humus are gardening terms that are often used in different ways. Although technically they both refer to decomposed organic matter, there are some subtle differences that account for the way gardeners use the terms.
What is Soil?
Soil is made up of 5 ingredients:
- Parent material: sand, silt, clay
- Living organisms: worms, bacteria, beetles, etc.
- Organic matter: active (decomposing) & stable (humus)
Soil is also made up of layers, or horizons:
- Organic layer: leaf littler, grass clippings, etc.
- Topsoil: primary root zone
- Subsoil: root zone for large plants
- Parent rock
However, not all layers of all soils contain all ingredients. The top layers of soil will have considerably more organic matter than deeper layers.
Not all soils have an organic layer. Some soils, like a sandy desert landscape, may not have any organic matter at all. The amount of organic matter in a soil depends on the amount of dead or dying plant material that falls onto the soil each year, and whether or not the environment is suitable for decomposition. (Learn the difference between Soil vs. Dirt).
The amount of living organisms, gas, water, and organic matter can fluctuate in each soil, and some may not be present at all. However, all soils must have parent material in order to be a true soil.
Growing Media vs. Soil
So, if soils have parent material, living organisms, and organic matter, what about seed starting mixes or raised bed mixtures? Are they not soil?
Growing media is the term for any material that holds a plant’s roots while it grows.
Soil is one kind of growing media, but there are many other types of growing medias for different growing systems.
Seed starting mixes, coconut coir, rockwool blocks, raised bed mixtures, and many other mixes and materials can be classified as a growing media even though they are not classified as a soil.
Difference between compost and humus
I'd like to top dress our whole lawn and at the same time seed areas that need to be filled after last years' racoon damage (yes, we had grubs). What's better to use? Compost or humus? Is there a difference? We also have 2 areas that seem have alot of clay with one area needing to be graded higher by about 2 inches or so. Should I just lay the compost or humus on top or should I till it in? Thanks for your help!
I'd like to know the answer to this too.
I use aged leaf humus because compost isn't available.
Isn't compost more broke down than humus?
I would top dress with compost. I think humus is just broken down compost. Here's a link. http://en.wikipedia.org/wiki/Humus
I forgot to add that my hubby double digs all of our beds to add the humus. He's my hero--it's really hard work.
Wow, double digging is hard work. Don't let the Lasgna gardening people know about it. LOL.
Well, drainage can be a problem here and the double digging has done excellent. We also add peat or sulfur and worm castings if I can. I still layer newspaper, humus and coffee grounds on top too.
Good thing we have a small yard. And hubby has strong muscles.
Dean - Thanks for the info. I always forget about Wikipedia, duh?! I read your link on humus and then compost. You're right that it seems humus is just compost that has been broken down more - at least that's how I interpreted the definition too. Well, we didn't top dress this spring but I always use Ringer Lawn Restore for fertilizer and suprisingly the lawn has really filled in from the racoon damage. I'm so glad of that. Here, fall is the best time to seed - can I topdress the compost then do you think?
I learned something new today!
I was always curious about the difference because my mother in law always adds humus before planting new plants. Her stuff always talks right off and grows huge! I always thought compost was the thing to add. Probably adding both compost and humus would be best!
I'm not sure what the best times of year for top dressing with compost are, medinac. Especially since your in a different climate than me. Hopefully, someone else can answer your questions here.
First. the word compost has to have a common content to which all understand.
. Start by telling us just what your medium you call compost is comprised of. Then is it half done or absolutely finished. Define finished. Only with some reasonable understanding of the basic truths can any real communication be meaningfull.
. One leading authority on compost indicates that it must be a totally rotted or converted mass consisting of: manures, many different plant parts in a brown green ballance of about 20 to one, native soil, added trace minerals and enough moisture to remain damp. This mass to be held above 115 degrees for a minimum of three days and slowly cooled back down to ambient area soil temperatures. At this point there should be no part that can be identified as to what part it used to be. The color will be rich brown with an earthy pleasant smell. If the compost being discussed is other than this it should be identified as the major part it came from. leaf mold or compost, all waste plant compost, mushroom waste compost. Commercial steaming of whatever they call compost kills the biology we are trying to build up. Therefore how can it be called compost? In fact all commercial compost that was steamed or chemically treeted can hardly be called compost. It is not if the biology has been killed to give it shelf life and confuse the meaning of the word.
. Today there are so many changed meanings of the word compost that none have a common basic meaning. Understand that if you have real finished compost the commercial world could not bag and merchandise it. Some will even and quite commonly make statements that tend to scare one from making and using the real compost.
Real home made best of all compost contains a host of live biology players. Only a few of the organic sites have taken the time and money to assure commercial quality. Perhaps a few local nurseries may have real good compost but you have to do the research and ask the hard questions. The problem is there is no consistant and legal specific content for products called compost.
Anyone making the claim that compost would burn is bluffing, lying or streaching the meaning of the word compost to include raw components of compost like manures that are not converted in process therefore not finished compost. To sight an example I ask about the compost at a local firm. The answer I got was our minimum sale is three yards. a yard of mushroom waste, a yard of two year old leaves and a yard of top soil all mixed to make our best compost. Half decent it was but compost it was not! I passed on that one.
I know a commercial lawn service that top dresses lawns with that mix which does not sound to bad. He calls it his Premium Lawn Dressing and charges like the dickens to apply it. The going rate for mushroom waste is twenty bucks a yard here, the leaves are free for the hauling and top soil goes down for about fifty bucks a yard. more if it is really good.
This message was edited Jun 30, 2008 12:54 PM
Is that a good compost, according to you?
Yes the whole biological mass will be better than any of its raw contents. All types of life will be improved and made still better by higher forms of life as it is worked back into the soil. Today we know how to make aerobic teas from our compost. This raised the bar of excellence for those who learn how to do this. The compost can only be as good as its total parts. The teas even aerobic teas can only be as good as the source compost.
The basics have always been and will always remain. Manures, mixed browns and greens, native soil, remineraliztion followed by cover crops to increase organic content and to protect from weather elements that would erode the soil by wind and rain. Any way these elements get into the soil and given time to be converted is fine. Composting the elements does it faster but not better than existing biology of the soil. Given time all the benefits of composting can be achieved many ways.
You folks in the New England States have North Country Organics in your backyards. They make an aerobic tea quality compost that is shipped damp in a bag that permits oxygen to get into it. If it completely drys on someone's sales shelf or your shed the value is lost. Their vendors are trained to keep it alive. Their tea quality compost contains all of the soil's biological players from bacteria, fungi and higher life forms from amoba to nematodes. None of your big box stores have anything called compost that even touches on the quality of real high quality compost. Your soil can not be biologically improved by a lot of stuff called compost today. In these instances the soil biology must first re-innoculate the purchased compost before any good will come of its use other than structure improvement. The major reason for making good or purchasing good compost is to immediately improve your soil. This requires the life to be in the bag.
So leaf mold really isn't compost, it would fall into the category of humus?
Leaf mold is a life form in its own right.
Leaf mold is rotted leaves that were broken down mostly by fungi. If you smell them they smell like mushrooms or mushroom compost. They are excellent organic content for your soil. It has allmost the same value as raw manures when the soil biology finishes the conversions into humus. The PH when fully converted by the soil or in compost is about 7.0. This is about the same as any living plant going through the process of rotting and being fully converted.
If I had a choice of just one item I could use the choice would be leaves in any state or condition.
That's good news! I do not do a compost pile with greens and scraps but I do chop up our fall leaves (which is a sizable amount) with a the lawn mower a couple times or with the Leaf mower and compost them in a bricked area back by our shed. They are slow to decompose but when I need some I dig the good stuff out from the bottom and use it as a soil amendment for new plantings.
Mixing some green grass clippings, or green shredded plant litter into your leaves would speed up the process, but not alter it a great deal. The idea of "composting" is to speed up the natural process. It all goes to the same place, it just gets there faster when you mix it in something close to the right ratio, pile it up to conserve heat and turn it periodically to reintroduce oxygen.
Unless you want to get way deeper into soil science than most gardeners want to, think of it like this -- humus is what happens naturally to the leaf litter, deadfall, etc. in the woods compost is the result of man stepping in and speeding up the process. Your crib of leaves is somewhere in the middle. It won't decompose as fast as a carefully controlled compost pile, but much faster than the leaves would in the woods.
Good post. It does get a little confusing to anyone begining to try and understand.
I live near Springfield, MO. The city has a wonderful composting program, run by a Master Gardener who is as devoted to recycling and organic practice as anyone I have ever met. She runs the program with an iron fist and a killer smile. The product they sell for $15 a yard is dark, sweet smelling and has virtually no decomposed matter in it. I have used it as lawn topdressing and garden soil amendment for a couple of years now.
In another thread on this forum, someone asked if it was okay to garden in pure compost. I didn't chime in that compost should be an amendment, rather than the complete soil, but I was sure someone would, and I was right. However, a few posts later, someone from the next town over from me posted pictures of her garden grown in raised beds filled with nothing but Springfield compost. Her garden puts mine to shame, where I carefully mixed the compost with topsoil, sand, and rice hulls.
Not wishing her any bad luck, but is her garden going to be all foliage and no fruit? What's your position on pure compost as a growing medium?
HUH ! All compost ammendments I have ever seen or read about suggest maybe an inch of good finished compost into the top four inches of soil. What may be putting yours to shame and ruining hers could be over fertilization using the man made type. There is no NPK in absolutely finished compost. It is an ammendment to fire up your biological community that will then create the natural NPK and other goodness as the main purpose in life. Most soils have some organic content that has not been converted to humus. The compost enables the native biology to expand and it is it that greatly expanded biology that makes the conversions in humus and the next step humic acid. After all this mystery transpires the plants have something they can use while the soil tilth is also improved.
I say something is going on that we are not aware of. Your rice hulls might be tying up your nitrogen. Give it time and you should recover and get better growth. Keep adding each year but do as much raw material adding as possible in the fall and then use a cover crop. It will improve faster that way. The winter rye is easy to till in the following spring and digests quickly. You should consider using organic 4-2-4 or similar low number fertilizer some in the fall and some in the spring. I us 20lbs both times on aproximately 1000 sq. ft. On heavy feeders like pumpkins, mellons, and cukes side dress a little more fertilizer about one and a half to two months into your growing season.
If the finished compost is truely finished in that other patch something else has to be delivering the NPK to that compost pile. which is what you described.
I don't know why it's taking 4 posts to happen before I get notified but I am NOT ignoring your wonderful information (especially when I started this thread). This is a great educational process for me. Thank you. I used to bag up those grass clippings and give them to the trash collector! Argh! I did get smarter this year and put the mulcher on the mower. Now I'll have to bag some clippings and throw it on the leaf pile.
Also, my husband has a license to keep quail for dog training/hunting. Should I be utilizing their poop as well? I wanted to throw it in the veggie garden area and let it sit over winter and in the leaf pile as well but don't know it that's healthy?
Oh yes. absolutely it is good poopers but any bird manuer is hot stuff. I speak in 1000 sq. ft. terms. You have to monkey it down or up to your need. I would not apply more than two five gallon buckets full to a thousand sq. ft. and I would do it just before planting a cover crop in the fall. Try that and adjust by experience. I quoted modest use. A little more or less will not hurt but don't go mad scientist for me because to much is worse than being skimpy. Said another way that is a very light sprinkling over the patch. Try to get it into the ground instead of just laying on top. You still need a little organic 4-2-4 in the spring. 20 pounds or half a bag is what I use for the 1000 sq, ft.
You can sock it to your leaf piles. If you get to much in there you will be informed by the smell. Then add more browns to calm it down. Mix a little soil in your leaf piles too. That will help the bacteria get cooking. I dump all my bed edge trimmings in my compost pile too. I see some darn good compost in your future. The bird feathers are good to. Feather meal is expensive.
Just to be clear, I'm delighted with the growth and productivity of my garden, I was just surprised by how much foliage the other poster, who is just a few miles from me, had on similar plants. Just pics, no science and no direct comparisons. just an internet observation. Everything is going well in my raised beds, and I have a quart of fish emulsion/kelp mixture coming to do a little side dressing.
Throw all the poop in the leaf pile and you won't have to worry about the concentration issues that docgipe mentioned. Also in the leaf pile put the grass clippings you mentioned, all your kitchen scraps (veggie only, don't compost animal product unless you really know what you're doing), tea bags, coffee grounds, weeds you pull out of the garden (the heat will kill the seeds), and any herbivore manure you can get your hands (shovel) on. Water it any time it looks dry. Turn it every time you think about it. Do it with a bit of concentration when the leaves fall and by March you'll have the best garden amendment you could ever find or buy.
Okay! In with the poop! What a great way to dispose of it. And now that I know, all the pheasant, quail and duck feathers will go in too. Again, thanks for the info and I'm saving this thread to refer back to.
Anytime I see tall, lush and dark green foliage I know the soil is over nitrated. There is no other reason for those conditions.
Be pleased with generally less tall, more open and lighter green plants. They are the healthy ones. The others are fat and sassy needing to be put on a diet. Most of the Better Homes and Gardens pix you see are extensions of greenhouse practice. over nitrated and more difficult to manage from all aspects but they are only grown for one picture or article. The beauty in a professionally managed show place is usually managed for the short term. tall, lush and dark green after which they dig or pull them out and put in another short term chemically managed planting.
Oh, Dwaine, I just hate that idea. I mean I know it happens - there's a college down the street that puts in new annuals every six weeks! (Doesn't necessarily have to do with fertilizer, but can't they spend their money on a more balanced planting that will look good for a longer time? And I'd love to have some of the things they dig up and throw away - like daffodil bulbs, or begonias, or impatiens - I could at least get another two months out of the impatiens!)
Sorry what you and I have just touched is the showplace philosophy and management. Most have more money than they know what to do with and won't move a finger let alone a shovel or hoe unless a grant covers the garden or project.
Two of our near by showplaces are Longwood Gardens and Hershey Gardens. where one season growth is all lots of bulbs or plants are managed to see. Hundreds of my bulbs came from Hershy Garden's spring plant sales. They don't even know how to grow them.
They only plant top rate bulbs and sell them all at excellent low prices out of the ground the following spring. Those showplace yard sales are a hoot. It's a shame on one hand. On the other hand most are well supported with company funds plus gate entry moneys. My neighbor got bare root three year old roses for two bucks a pop while one of the above was making room for the new roses.
When I come out of those stinking. stinking from constant preventative spray material I look for the non-existant shower room and a wash basin to clean my shoes.
We commoners. (smile) have to keep those bulbs for a lifetime and likewise the roses save a few that just wear out. I've been looking for private sector grant sponsor interested in organic principles. Don't hold your breath. :)
I've been trying to track down the landscaping department of the aforementioned small college. It's big enough for a website but not big enough for the landscapers to be on the website. If I could catch them in the act I'm sure I could act all friendly and come away with more free plants than I could use. The tulips I don't mind so much but the daffodils.