Is a compost pile ever "done?"
May 31, 2010 2:15 PM   Subscribe

Newbie composting question: How is your compost ever "done" if you keep adding new kitchen scraps and material to it?

I'm considering purchasing a rotating compost barrel, but I don't understand how composting works. I get that you add vegetable-based kitchen scraps, weeds, grass clippings, small branches, etc. Over time these break down, but everything I've read says to keep mixing in new scraps, wetting down, and mixing. If you keep adding new material, how is the compost ever "done?" Do you reach some point at which the compost container is mostly full and then let it sit for a few months without adding any new material, then empty it and start over? At what point do you have a container full of soil-like material, the kind you can purchase at the gardening store?
posted by mamessner to Home & Garden (15 answers total) 11 users marked this as a favorite
I keep two bins, one to use while the other is sitting for a few months; you do need to stop adding material if you want the compost to ever be "done." I know mine's ready when I can stick my hand in the bin and not be grossed out.
posted by MrMoonPie at 2:20 PM on May 31, 2010 [1 favorite]

When I was a kid we had an old coal bunker and we'd put all the rotting stuff in the top and a combination of gravity, pressure, time and bacterial action would produce this super rich mulch at the bottom where you'd normally shovel out the coal. It wasn't soil, as such, it was something much more disgusting, but it was good enough to grow freakishly delicious runners beans. Maybe the whole thing is a vertical process.
posted by tigrefacile at 2:23 PM on May 31, 2010

Do you reach some point at which the compost container is mostly full and then let it sit for a few months without adding any new material, then empty it and start over?

Yes. You need at least two containers, so that you have somewhere to start a new pile while the first pile finishes composting. If you want/need to turn over your first pile to ensure good composting, then it makes sense to have three containers.

At what point do you have a container full of soil-like material, the kind you can purchase at the gardening store?

While under ideal conditions in a rotary composter you might be able to reach this state in a matter of weeks, realistically you are going to have to wait for months.
posted by ssg at 2:23 PM on May 31, 2010

You have to stop adding new stuff to let what's in there finish cooking. So yes, quit when it's maybe half full and let it finish. This might take a few weeks or longer, depending on what you're putting in, and maybe whether it's in the sun or not. You'll know it's done when it looks like nice black compost, without visible remnants of food (except maybe an odd eggshell, if you're putting those in to add calcium). Meanwhile you can store your scraps in sealed plastic buckets, or just start a traditional compost pile. Which, truth be told, is just as effective and a lot cheaper, although it takes longer.
posted by beagle at 2:24 PM on May 31, 2010

We have three open bins, one of which is always soon to be done. The compost smells really good when it's done, like really fresh dirt, if that makes any sense. New stuff goes into its own bin. If you only have room for one bin, you can get a big garden sieve, and use it to sort the done stuff from the new stuff.
posted by pickypicky at 2:26 PM on May 31, 2010

Do you reach some point at which the compost container is mostly full and then let it sit for a few months without adding any new material, then empty it and start over?

Pretty much. Personally I don't use a rotating barrel. I have a large non-rotating barrel with a door at the bottom. I rotate the top foot or so of material manually with a fork every now and then (but not religiously). And because my barrel is open to soil at the bottom, I get a lot of earthworms in there. That works pretty well for me - the stuff coming out of the door at the bottom is pretty close to store-bought compost, as long as I'm not taking too much out. And as I remove compost from the bottom, I get room at the top for more waste. Realistically, I can't get remotely close to meeting my need for compost by making it myself, though I do my best.

If I had a rotating barrel (which, it must be said, will compost a fixed volume of waste a bit more quickly), I wouldn't use any of the compost if there was anything newer than a couple of months in the barrel. I'd either go for two barrels, or empty the full barrel into a corner of my vegetable garden and leave it a while.
posted by le morte de bea arthur at 2:27 PM on May 31, 2010

When I was looking at rotating composters I also caught that you have to stop adding stuff to let the compost finish doing its thing. So I got one of these instead- it has three levels, so you put kitchen and yard stuff in the top and mix that, and then after a month or so drop it all down into the next level, where it continues to cook, and you can start a new batch on top again.

Basically, it's more than one bin, just stacked vertically to save space. And it takes probably three months to go from kitchen scraps to compost, but I like it because I can keep adding stuff on a regular basis, and it doesn't take as much room as multiple piles or rotating barrels would.

Have you considered a worm bin? I don't have one myself but I understand worms turn kitchen scraps into compost faster than a compost pile and you can continue to add scraps to the bin on an ongoing basis.
posted by ambrosia at 2:43 PM on May 31, 2010

Turning garbage into dirt isn't rocket science, and it's pretty hard to get it wrong. If you want to be fussy, sure, get separate bins. But it's not necessary. A pile on the ground works just as well as a bin made for the purpose. Just keep adding layers of refuse, sprinkling occasionally with lime. Note how warm the middle of the pile gets as bacteria do their thang. More or less, shovel the compost out from the bottom of the pile. If it smells sweet, you're good to go. If it doesn't, wait.
posted by Short Attention Sp at 3:18 PM on May 31, 2010

Just keep adding layers of refuse, sprinkling occasionally with lime.

Sprinkling compost with lime doesn't contribute in any way to forming compost, and has the potential to slow it down, as lime will kill certain decomposing microorganisms (this is why lime is used to minimize the smell of decomposition). Lime can also contribute to nitrogen loss in the form of gaseous ammonia, if the lime causes the pH of the pile to rise above 8. A good, aerobic compost pile will regulate its own pH.

Rotating barrel= not necessary, BTW. Frequent turning of compost doesn't help it go any faster. Turning compost is done to aerate it, but if you've built a pile of a good mix of various browns and greens, the texture alone provides the porosity needed for aeration. Turning does immediately increase oxygen levels, but only for an hour or two before they go back to what they were before turning. A once a week stir is good to help homogenize the pile, but not really necessary otherwise.

I think if you want to just keep adding food scraps, ambrosia'a suggestion of a worm bin is a good one. That way you can add and harvest worm compost regularly once it gets going. Otherwise some of the compost management suggestions, such as having two piles, is what most people do.
posted by oneirodynia at 7:48 PM on May 31, 2010 [1 favorite]

I've had a rotating barrel for years, and now I use it mainly as a holding bin for kitchen stuff fresh enough to attract unwanted visitors.

This is why I'm going to third ambrosia's suggestion--kitchen waste should go into a worm bin. Your compost pile should consist of dead leaves, grass clippings, and other yard waste--stuff animals won't bother with.
posted by Camofrog at 8:05 PM on May 31, 2010

Also, if you do go with a rotator, don't add fresh grass clippings or green leaves or weeds to it. You want to balance out all the wet funky kitchen stuff with dry brown carbon stuff. Mulch hay, for example, would be ideal, or dead dry leaves.
posted by Camofrog at 8:08 PM on May 31, 2010

If you're not going to go with a two bin system (which is a nice solution, btw), you should just sift. A 1/4" chicken wire on a few 2x4s can sort out the good stuff from the not yet ready stuff.
posted by Gilbert at 8:54 PM on May 31, 2010

Piggy back question:
A long time ago I found plans for a solar-powered, self turning composter, using a regular small panel and very tiny gear on a motor to a very large gear on a 55 gallon drum.

Now I can't find it, and I have mostly unlimited access to 55 gallon food-grade barrels that have washed free from docks and are sitting along our river, and I need a compost barrel.
posted by TomMelee at 7:22 AM on June 1, 2010

Response by poster: Thanks for all the help. I did a little research on composting as part of my MBA. We were doing a consulting project for Fiskars. We invented a rotating composting barrel that would attach to your hose and was water-powered. There was a valve so that the hose water could go straight through (and act as a normal hose), or, if switched, would mist the compost and slowly turn the barrel. The idea was that it would automate the wetting and turning, be easy for the elderly to use, and would remind you to turn your compost every time you used your hose.

They didn't bite, but I still think it could be a good idea. Thoughts?
posted by mamessner at 11:53 AM on June 11, 2010

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