Do you add soil to your compost?

tcstoehrNovember 4, 2010

I was told to do this years ago but ignored the advice. Then I read Steve Solomon's writings on compost and he advises a layer of soil here and there within the compost pile. After thinking about it, it did make sense. Introducing the soil organisms into the pile makes sense since they cannot move there themselves, not at the rate they're able to travel.

I've always noted how much faster leaves decompose when laying on soil. So I started adding thin layers of soil into my compost bin. And I have to say it has made a difference in my usually warm (not hot) compost. My compost gets one turning and one year to mature before being used. Adding soil to the compost has definitely helped it mature faster, meaning that I end up with a finer, crumblier, more finished product.

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hortster(6a, southcentral KS)

Interesting article on home composting attached. I usually use thicker layers of OM and thinner layers of soil than they recommend, but I have a slow 2-3 year cycle because 1) I am lazy and 2) the ol' back won't let me turn it often enough. Usually use a couple of pounds of urea on top of the OM and under the soil layer. Sod stripped for making new bed areas works great as a soil layer since it holds together across the top of the pile and doesn't wash off or pile up in the middle - I toss it in there upside down to kill the roots and keep the stripped sod from continuing to grow during wetter periods.
hortster

Here is a link that might be useful: one home composting method

    Bookmark   November 4, 2010 at 5:09PM
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Lloyd

I do not intentionally add soil but some of the plants that have been yanked out have soil on them. The windrows are also on the ground and when I use the skidsteer to turn, some soil would be scraped up as well. I can certainly understand the thought behind adding soil.

Lloyd

    Bookmark   November 4, 2010 at 5:20PM
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luckygal(3b)

Can't really keep soil out of the compost when pulled weeds are added. If I don't have weeds to add I often just pull wild yarrow from outside the garden with roots and soil attached. I have a couple of times added soil from the forest floor because I read it was a good idea. I don't however do a layer of soil, just a sprinkling - might help and can't probably hurt.

    Bookmark   November 4, 2010 at 8:47PM
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eaglesgarden(6b - se PA)

I added a few shovelfuls of soil when I first started my compost bin. I figured it would have most of the microbial life needed for the compost bin, and would help it get started. It was free, as opposed to buying a jumpstarting product. I don't know that adding the soil helped, but I'm pretty sure a couple of shovelfuls mixed in a cubic yard of material is not going to hurt either.

    Bookmark   November 4, 2010 at 9:00PM
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bpgreen(5UT)

If you're composting in a clean room, you'll need to introduce microbes, but bacteria and fungi are everywhere. If we needed to inoculate something to get it to rot, we wouldn't need refrigerators.

    Bookmark   November 5, 2010 at 2:21AM
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Kimmsr(4a/5b-MI)

Because the people at Indore always added soil to the compost they made Sir Albert Howard thought it necessary to do that. However, later research showed that the bacteria in soil and the bacteria that digest your compost material are not the same and adding soil is not really necessary. It is not really necessary to add soil to your compost but it is not needed.

    Bookmark   November 5, 2010 at 6:21AM
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eaglesgarden(6b - se PA)

I knew it!

Yeah, even as I was adding soil to my pile (even just a little) I figured it wasn't going to amount to anything, but I figured it wouldn't hurt either. But, over the years, I'd added so many leaves to my garden and other OM, I figured that there were some microbes there that would benefit me. The key is that I have a firm belief that it did nothing to SLOW the process, even if it may not have actually improved it.

    Bookmark   November 5, 2010 at 7:59AM
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gargwarb

If you're composting in a clean room, you'll need to introduce microbes, but bacteria and fungi are everywhere. If we needed to inoculate something to get it to rot, we wouldn't need refrigerators.

That sums it up very nicely.

    Bookmark   November 5, 2010 at 9:15AM
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claireplymouth z6b coastal MA

I'm not composting in a clean room, but my OM is heavy on shredded paper and Starbucks coffee grounds. I figure neither of these are teeming with composting microbes.

I sprinkle in a handful or two of half-finished compost if I'm layering the material. If I'm energetically turning the material into the existing pile I don't bother to inoculate it.

Claire

    Bookmark   November 5, 2010 at 12:19PM
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tcstoehr

One of the things Solomon mentions is that there are soil-born bacteria that are capable of processing gaseous nitrogen (in ammonia) which otherwise would escape thru the air. I have no idea.
The notion that soil organisms spread into the compost pile would NOT assist in the breakdown of organic matter is, to my way of thinking, an absurdity. Perhaps because my composting is done by adding small layers at a time and I never get a hot pile going. Hot piles may be a completely different beast, I don't know.
In any case, I've made a point in observing the results of adding thin layers of soil as I build the compost pile for the last two years. The results have been surprisingly positive. It gets crumblier faster. I have truly finished compost in much less time. I'm glad I spent the effort to check it out.

    Bookmark   November 5, 2010 at 1:05PM
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seamommy(7bTX)

We compost in bins on the ground so it has soil in it. You may think it absurd to add soil, but I know that the compost in the bins gets finished a lot sooner than the compost in my tumbler.

    Bookmark   November 5, 2010 at 3:08PM
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unasmith

I have added soil to new compost piles where I had no old compost to use. I think the soil helps to get the piles started, but as much as old compost does.

    Bookmark   November 7, 2010 at 7:21PM
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bpgreen(5UT)

"I'm not composting in a clean room, but my OM is heavy on shredded paper and Starbucks coffee grounds. I figure neither of these are teeming with composting microbes. "

I've made compost that had little but UCG and shredded paper. I sometimes got it to 160F in a couple of days.

    Bookmark   November 8, 2010 at 8:08PM
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claireplymouth z6b coastal MA

"I've made compost that had little but UCG and shredded paper. I sometimes got it to 160F in a couple of days."

How? Did you turn it ferociously? I run a lukewarm to cold pile with minimal turnng and I've never gotten that kind of heat.

Claire

    Bookmark   November 8, 2010 at 8:14PM
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bpgreen(5UT)

I made a mix of about 50/50 UCG and paper, mixed it a bit and made sure it was damp and not wet. It heated up in a hurry.

    Bookmark   November 9, 2010 at 2:30AM
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claireplymouth z6b coastal MA

Thanks, my issues may that of much more paper than UCG. The grounds come with filters included and I have a lot of paper to deal with. I recently decided to try to compost all waste paper (except nose and toilet) and I'm still working out how to reasonably shred/tear the newspapers, catalogs, junk mail, bills, etc. and still have time for the rest of my day.

The only Starbucks close by is very accommodating but others forage for grounds there too, so I can't get as much as I'd like. I'm also not willing to put too much physical effort into turning the pile.

Consequently, my compost pile is dominated by fungi, as you can see from the photo from last July:

Right now I'm pushing a bit so that when I start spreading the compost within the next few weeks the pieces of paper won't be too obvious.

Claire

    Bookmark   November 9, 2010 at 11:20AM
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oliveoyl3

Revisiting this topic of interest to us soil makers...

The link below states a 74 minute discussion, but it's really done at about 54 minutes.

Some interesting suggestions:
-add 5-25% by volume soil to compost piles to retain nitrogen (instead of creating ammonia gas) He also states adding clay soil is essentially creating activated humus that retains the potency.
-add large & hollow stalks for air supply (corn, sunflower, etc.)
-build heap with material 2x year when gardening waste accumulates (spring when overwintered plants go to seed & fall after harvest) & also add dry saved as accumulated (spread in 3" layers to dry out for storage) rather than a continuous compost pile
-size of pile should be at least 6' wide & 5' tall (gather materials from elsewhere if you don't have enough)

His composting yard has 4 working heaps:
dry accumulating vegetation storage (when kept dry will not compost yet)
new compost heap (made in last 6 months)
recently turned & moistened (goes for another 6 months)
last turned heap

Heap techniques he uses:
-creates heap (2nd person sprays water lightly as constructed)
Covers with thick layer of fluffed up cereal grain straw to insulate & shed water (could overlap as flakes instead of fluffed up in rainy climates) Save straw as the layer, so strip off before turning heap.

-adds nitrogen such as: canola seed meal or livestock manures during heap building
If a lot of manure composted add a lot more soil to handle the nitrogen (soil slows it down to prevent rapid decomposition & fertilizer loss)

-6 months later turns heap (sprayed again with water as turned)
-lets heap sit covered another 6 months

Steve Solomon's most recent book is called The Intelligent Gardener: Growing Nutrient-Dense Food

Here is a link that might be useful: STEVE SOLOMON ON MAKING GREAT COMPOST

    Bookmark   February 9, 2014 at 1:27PM
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nc_crn

The main drawback to adding soil to compost is the addition of weight and bulk which makes turning + hauling more difficult.

I am a HUGE advocate of having a soil + compost mixture in your final in-ground soil. The mineral portion of a total soil is far-too-ignored by some people. A "soil" that is almost nothing but fluffy organic matter is nothing close to a healthy soil, in my opinion/practice. The mineral portion of a soil acts as a "battery" holding onto some of the good stuff the organic matter portion is producing to begin with...along with adding it's own positive additions to total soil health.

That said, I wouldn't worry too much about adding soil to a compost bin...and if I did, I would keep it closer to 5% than 25% from the advice given above. Retention of N by the addition of clay/silt to a pile is a bit overblown in importance if you're going to be turning it. Even in the best and balanced mostly-undisturbed soils you're going to lose a lot of N to volatilization and leeching...it's just a function of how easily N moves in both air and water even with proper sites for nutrients to attach.

    Bookmark   February 9, 2014 at 5:37PM
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lazy_gardens

I top some of the bins with a puddle of dirt and plant tomatoes or squash in them.

I'm doing "cold composting" to the extreme ... pile it and forget it until I need compost, then break the bin down and remove the good stuff.

The usual course of events is that the bin shrinks to 1/2 or less of the starting height, I remove the veggies, fill it up again with more compost ingredients, another puddle of dirt ... repeat as needed. This way I get double-duty out of the bins: it's an elevated planter and it's turning into compost.

Because of the climate, all of my bins have a drip line in them to keep them moist.

    Bookmark   February 9, 2014 at 10:12PM
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Kimmsr(4a/5b-MI)

The bacteria in soil and the bacteria that will be digesting the material put into the compost pile are not the same gals, which means adding soil to a compost pile does not add any bacteria that will help with the composting process.
If adding soil to your compost makes you feel good go ahead and do that, just understand it will do little for the process.

    Bookmark   February 10, 2014 at 6:58AM
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tropical_thought(San Francisco)

You can add soil, but if you add too much you will slow down the process. If you don't want to add it, that is also not a big deal either way. If the soil is a fine it will block air circulation, which will bad for the process. I some times add it if it was coming along with some other material I want to compost like leaves. I don't add it just for the sake of adding it.

    Bookmark   February 10, 2014 at 7:46PM
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seysonn(8a WA/HZ 1)

If I had to compost a lot of greens, grass clippings in the summer time, I will add thin layers of some kind of soil, old compost or manure on layers of greens. This sandwich effect should help the process. JMO

    Bookmark   February 10, 2014 at 10:28PM
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Kimmsr(4a/5b-MI)

I have not found, in the lists of material to compost, Cornell, the University of Florida, Oregon, Washington, or Organic Gardening magazine, or any other knowledgeable source soil as part of the mix.
There simply is no good reason to add soil to a compost pile.

    Bookmark   February 11, 2014 at 6:47AM
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tcstoehr

I consider Steve Solomon a knowledgeable source, particularly for Cascadia gardening. He specifically lists garden soil as a necessary component of producing high quality compost. And he gives his reasons why. If you read his latest book "The Intelligent Gardener: Growing Nutrient Dense Food" you will find a source that has so far eluded you.

    Bookmark   February 12, 2014 at 12:58PM
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toxcrusadr(Zone 6a - MO)

What I would like to know, without reading his book, is what microbes are in soil that are beneficial to the compost that are not already in garden and food waste.

kimmsr seems to have an answer for that as well, in the other direction.

Let's hear them.

    Bookmark   February 13, 2014 at 5:09PM
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oliveoyl3

SS says soil added to compost helps make high quality compost with fertilizing power because clay soil binds with nitrogen. Otherwise the high level of nitrogen turns to ammonia gas & dissipates. The compost is still organic matter, but doesn't have the fertility it could have.

I noticed that when I started using org. fertilizer in my vegetable garden beds plants grew more quickly in my limited summer sunshine. In my clearing in the woods by mid August the sun lowers into the trees plummeting my direct sun hours. In addition, we receive over 55 inches of rain yearly Oct-June, so fertility is washed away.

I'm interested in creating homemade compost with more fertility to avoid purchasing amendments. We have rabbits, various poultry, & goats have lots of nitrogen-full manure plus bedding.

    Bookmark   February 13, 2014 at 5:48PM
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nc_crn

Steve Soloman says lots of things...and he has critics of some of the things he says even if most of it is good.

The amount of N held by adding soil/clay to a compost pile is rather miniscule. It helps, but not much...especially if you turn it. Clays/silts help hold N...as well as other nutrients...but in an active pile it doesn't benefit very much. It's action is best achieved in an undisturbed-yet-active soil...and even then you experience great losses with air/water/heat (all 3 of which you should find in excess in a compost pile).

He has a hand on some information, but the scale of it's benefit is what he's lacking. Where he came to suggest 5-25% as an amount to add is just odd...seems like something he randomly came up with. Adding 25% soil to a compost is a great way to add a lot of extra weight to your pile with very little benefit for why you're composting to begin with.

    Bookmark   February 13, 2014 at 8:19PM
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DirtandYarn(7)

Cornell does recommend a handful of soil if you don't have finished compost or accelerators to add. This was regarding worm composting.

http://compost.css.cornell.edu/faq.html

This cornell site recommends topping a new pile with finished compost or soil.

http://compost.css.cornell.edu/outdoorbest.html

    Bookmark   February 13, 2014 at 11:56PM
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Kimmsr(4a/5b-MI)

What I read is you can use soil or accelerators but they are not necessary.
That compost recipe, written for and by 4H, also lists ashes as an ingredient, something Cornell Composting does not recommend.

    Bookmark   February 14, 2014 at 7:22AM
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Lloyd

I'm guessing some people are talking about separate issues here and don't realize it. Adding soil to add different microbes versus adding clay particles to give something for the N to bind to. They are not the same.

Lloyd

    Bookmark   February 14, 2014 at 10:22AM
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toxcrusadr(Zone 6a - MO)

Agreed Lloyd. We were talking about microbes weren't we.

But on the N subject, if true, this would give credence to sheet composting and trench composting - get the nutrients into the soil even as the organic matter breaks down.

    Bookmark   February 14, 2014 at 11:45AM
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elisa_z5

Pulling this up, as the question was asked again.

    Bookmark   March 1, 2014 at 5:18PM
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jctsai8b(8B)

Thank You. elisa_Z5.

    Bookmark   March 1, 2014 at 8:05PM
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floral_uk z.8/9 SW UK

If you add pulled weeds to the compost you will be adding a little soil anyway because some will be clinging to the roots. I don't add it deliberately though.

    Bookmark   March 2, 2014 at 6:05AM
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