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Too much compost in the soil? Steve Solomon Intelligent gardener  RSS feed

 
pollinator
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While I really like the  book "the inteligent gardener" I doubt his view on compost, that too much compost can throw the soil out of balance.
Second there are a lot of people gardening were there was no soil before, what other method is there than to either build it up or sheet mulch?
Can too much compost or arganic matter really be bad for the soil?
 
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Too much organic material can be an indicator of waterlogged soil, for example I have areas that are over 50% organic matter, it is always wet so it goes anoxic  and does not break down that area is trying to revert to peat bog. To much compost can lead to leaching of excess nutrients just the same as too much of any fertiliser can. I assume that if you were to put say 2ft of compost down each year and not dig it in then you would not be getting down to the soil so plants wouldn't have access to the minerals present there, only those in the compost. Practically it would probably be very difficult to do that however as the amounts would be huge.
 
pollinator
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Skandi Rogers wrote:Practically it would probably be very difficult to do that however as the amounts would be huge.


That's how I look at it.  I can't see any way I am going to have too much compost to add, so for all practical purposes, I would say no, it isn't possible to add too much.
 
pollinator
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A lot of people do not realize it, but yes there is such a thing as too much compost. My soil has crept past "Above Optimal" on organic matter and it is at 7%. For us, we switched tto using liquid manure for awhile that gets the NPK in the ground, but without getting the organic matter too high. Seaweed also helps in the tilled soil as it helps lighten the soil.

When too much compost is present, it does not allow water to move through the soil properly.


 
pollinator
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In general I'd say "yes", soil can have too much compost. BUT, I'd have to add that it depends upon the situation.

On my main farm I add a couple of inches of compost between crops and flip it in. But I have to be careful. During wet years this can make my soil retain too much moisture. But on drought years I find myself wishing I had added more, and indeed I do add extra between crops when it's a dry year. That excess compost is the only thing that saves me when there's little rain.

5 miles away I have my seed farm. It's very warm, dry, and windy there. Lots of sun. As a result the soil.....what exists......dries out quickly. The compost degrades quickly. Rains tend to be infrequent but heavy, resulting in leaching. Thus I'm more aggressive on adding compost. In fact, I use pallet grow boxes there that contain 100% young compost and I grow 2 crops of seed (bean, pea, etc) before emptying the box and starting over. The old compost goes to help improve the ground soil on that little farm. I really don't think there is such a thing as using too much compost at that location.

10 miles away is a community built on fractured lava. No soil except the degraded organic dust between the lava chunks. I know of successful gardeners who haul in county compost by the truckload, often adding 1-4 pickup truckloads a month. I recently was visiting one place where the compost layer is now 20" deep after about 10 years of hauling. I'd guess they have about 1/4 acre covered in mulch. They grow in that compost all sorts of veggies and fruit trees. The area is in a dry zone with sporadic rain. I noticed that the compost layer was retaining moisture while the rest of their land was bone dry. In this situation, the excessive compost works for them.
 
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I call it the peat moss effect. Peat comes out of the bag dry, and takes FOREVER to get it damp. You almost have to soak it in a bucket.

The same thing can happen with too much compost,  or a mulch made from compost. If you water, and think you watered well, you may be surprised to find that it is bone dry 1 or 2 inches below the surface. The peat (or compost) absorbed it all.

I lost a crop of corn, thinking i was watering adequately. Texas summers......
 
wayne fajkus
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One more tidbit. I think its funny, if not oxymoronic. I think i watched (pbs- growing a greener world?) that 5% is the goal and that number is ruffly twice what occurs in nature.

But i bet everyone here has had a tomato, watermelon or potato sprout up from the compost pile.

 
Todd Parr
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wayne fajkus wrote:
But i bet everyone here has had a tomato, watermelon or potato sprout up from the compost pile.


That is one of the reasons I don't personally think you can have too much.  I have grown lots of plants in pure compost and haven't seen the negative effects people are talking about.  My clay soil retains far more moisture than my compost does, so the soil you are starting with must play a large part.
 
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As several have noted, there are other things that come into play when talking about compost quantity such as structure of the medium (dirt, the mineral proponent of soil) if you have a coarse medium then it will hold far more compost with no adverse effect, than a fine medium would be able to handle.
Dirt can be divided into several different levels of structure; coarse (gravels all the way from large stones down to below pea size) these structures have huge voids and thus can hold far more organic material than the next level down in size which is sand, then we go down in size to silt, and from silt we go down to clay.
At each level of coarseness (or lack of coarseness) the amount of organic material that is able to be contained goes down in mass until we end up at clay. The caveat of these structures is the level of coarseness of the organic material, which also plays the role of coarse to fine to super fine and the effects are very similar.
A super fine clay can hold a lot of very coarse organic material and as we move up to coarse gravel medium we go down in size of organic particles the medium is able to hold without becoming water logged.

What we need to be striving for is a balance of particle sizes that allow the best water holding ability and thus air holding ability put against where that blend looses the ability to vacate and pull air back into the soil as the water sinks deeper.

So, for every soil type, there is an upper limit to the amount of organic material it can hold and still be in balance.

Redhawk
 
Angelika Maier
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If you don't have dirt to begin with, how else would you build your soil than without compost? I use used potting soil which is sand cow manure and bark as well and some subsoil which I get from a crazy guy who digs out a cellar.
 
Todd Parr
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Angelika Maier wrote:If you don't have dirt to begin with, how else would you build your soil than without compost? I use used potting soil which is sand cow manure and bark as well and some subsoil which I get from a crazy guy who digs out a cellar.


In the thread called "Article on Starting a Nursery Business", the article talks about that very thing.  Basically, pile on as much organic material as you can find, in any form.  That is what I do on my place as well and I find it works very well.
 
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I think I've created a "too much compost" scenario in parts of my yard. Soil is terrible, and wanting to plant an avocado tree which requires well drained soil in a lower spot in the yard, I've piled up a lot of compost and mixed it with soil. Probably 70% compost mounded about a foot above the overall yard level, the hope was that through the winter with the rains it would break down some, but the soil life is so minimal that I doubt much will happen.

So I'm thinking I will add more dirt and mix it in and level out some this "winter", and plant the tree in a couple months. Not sure if I'll kill another tree or not.
 
pollinator
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I think Steve's idea is not so much that the extra organic matter will throw things off, but that the extra potassium brought in by the organic matter will throw things off.
 
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I would say that soil should only be 10% organic matter. If your compost is completely finished it will have around 10% organic matter, but most compost is not completely finished/aged and so it has alot more organic matter and quite possible alot of nitrogen which can produce nitrates in some vegetables (bad for your health) and that can also promote vegetative growth at the expense of fruit production and excessive nitrogen can make some shrubs/trees/vines not harden off properly esp if you are zone pushing. The soil life in compost is predominately bacterial vs fungal so in some technical sense it may not be what someone is trying to promote. 


Like everything else it depends and moderation but overall compost is very very rarely a bad thing so go ahead and add it.
 
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