Shelf life of compost?

raymondo17(z9 Sacramento)March 25, 2013

Does compost have a shelf life? Last fall, I took the contents of my compost pile, which was about 80% done, and put it in a large plastic trash can so I could start a new batch in my compost bin. (Gotta take advantage of all those falling leaves.) Fast-forward five months, and I'm wondering whether my old compost still has the same nutritional value as it once did?

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Even if the bacterial/microbe benefits have played themselves out, the advantage of a better soil structure via amendment and the ability to have an environment conducive to "recharging" what's left in the compost will help most soils.

Most nutrients, unless totally consumed by microbes and leeched/gassed-off to the environment (N, especially), will still be around in the compost even if microbe action has slowed or stopped.

    Bookmark   March 25, 2013 at 1:51PM
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toxcrusadr(Zone 6a - MO)

If it had a lid on it, the nutrients will not have leached out from rain, so that's good. But if it got dry in there, the microbes will be dormant and populations reduced. So it might have lost some of its potency, but it never becomes useless or harmful, so go ahead and use it.

Compost is always on a decay curve, and it's hard to suspend that process and store it w/o losing *something*. Always best to use it when it's in the 'ready' range, even if it's fall, and start making some more.

    Bookmark   March 25, 2013 at 2:47PM
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Karchita(WA Z8)

I'm thinking that if it has a shelf life, it would be a lot longer than just five months, especially over the winter. If stored out with a lid and not totally dried out and still has worms in it, I think it would be fine for as long as a year or two, and after that it would still improve soil structure.

Those bags of compost they sell at garden centers sit around for many months.

    Bookmark   March 25, 2013 at 4:46PM
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toxcrusadr(Zone 6a - MO)

I don't think it would ever be totally useless. There was someone on here last year who found a 10-yr. old bag in the back of the garage, had it tested, and found the nutrient values were just fine. And any kind of humus - whether any NPK remains at all - is a good soil amendment.

This post was edited by toxcrusadr on Tue, Mar 26, 13 at 10:47

    Bookmark   March 25, 2013 at 6:49PM
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raymondo17(z9 Sacramento)

Thank you for all your words of wisdom. Good to know this compost will still go to good use. :)

Happy springtime, everybody!

    Bookmark   March 25, 2013 at 8:34PM
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As Tox has indicated above compost is always on a decay curve so it would have a shelf life which will depend on many things such as moisture content, temperature, and the quality of the compost itself. Several people have come here and stated they did not like to use compost, or organic matter, in their soil because it "disappears" indicating that that compost or organic matter was alive.
Sealed in an airtight bag could cause compost to become anaerobic, or could create other problems for those aerobic bacteria that compost should provide. However, if the compost was dry enough that the bacteria entered dormancy an airtight plastic bag might not be much of a problem.

    Bookmark   March 26, 2013 at 6:39AM
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Raw_Nature(5 OH)

Charles Wilber - how to grow world record tomatoes.. From what I remember he stored his compost in huge garbage bins for years... He said as long as you keep it moist and keep a lid on it so rain couldn't leach anything out of it, it'll last... He recalled a time when he has 5 year old compost that he brought to a farmers market, people were amazed at the quality! Matter a fact, I think that aged compost is what he used on his 30 foot tomatoes... Keep it moist, but don't let water leach out of it.. I wouldn't get it air tight as it would go anaerobic and ruin! If you use a few precautions you'll be fine! Don't worry!


    Bookmark   March 26, 2013 at 10:04AM
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Atmosphere loss of N (especially NH4) is the biggest negative of very old compost. No lid can contain these losses, especially if moist...unless the lid is air-tight...which would cause other issues with compost health, especially if moist. Most other nutrients will not gas off in noticeable amounts, though.

    Bookmark   March 26, 2013 at 3:57PM
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I'd be surprised if mature, stable compost gave off any N. CO2 sure, but not N.


    Bookmark   March 26, 2013 at 6:51PM
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All soils with N content are prone to volatilization (gassing off)...that said, you're not going to lose all of it, especially deep in a container unless it dries out out to the point where oxygen and heat can act upon it. Well, even then you're not going to lose all of it, but those conditions hasten the gassing off beyond the surface level.

The NH4 breaks down to NH3 and H2O...the NH3 gasses off into the atmosphere. If left undisturbed, this isn't much of an issue in deeper profiles (in this case deep in a container) until moisture, moisture/heat, or heat/drying (or pH in extreme cases) act upon it.

This post was edited by nc-crn on Wed, Mar 27, 13 at 3:02

    Bookmark   March 27, 2013 at 2:49AM
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One of the tests for compost maturity is a volatile ammonia test, it has been my experience that my very mature compost doesn't register any. Nitrogen conservation can be achieved with the right parameters.


    Bookmark   March 27, 2013 at 7:25PM
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tropical_thought(San Francisco)

I find that I get better results with younger compost.

    Bookmark   March 27, 2013 at 7:34PM
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Finished compost runs about 1-1-1. So unless you're growing in pure compost, you're not getting a lot of N-P-K from it in any case What you are getting is a great soil amendment that helps retain water and hold nutrients in the soil for later plant access. And you also get micronutrients.

    Bookmark   March 28, 2013 at 5:43PM
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I agree with toxcrusadr.
I have a few thousand pounds of finished compost that has been laying in piles for 4 or 5 years now.
I used it & give some away every spring & do not use bag NKP organic or other wise for the last 5 years. I even turn in raw leaves, grass clipping with no noticeable lost of N.
But like any plant bed the type of soil & how much OM you have in it will make a difference.
But I would say a long shelf life, far more then 6 months.

    Bookmark   March 31, 2013 at 10:01PM
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If you have compost that has been sitting around for a number of years that should be an indication of a lack of bacterial activity, or dead compost. If one of the values of compost is the bacterial activity and those wee buggers are busy digesting that compost it should, one day, be all digested, gone.

    Bookmark   April 1, 2013 at 6:59AM
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