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bensmithmath

adjusting green/brown mix

bensmithmath
9 years ago

I've had a couple of big piles building up for a couple months now. I've been getting about 10 gallons of coffee grounds per week from my school's coffee shops, and mixing it with straw I got from bales, and smaller ammt of kitchen scraps.

So coffee grounds are about 20:1 and straw is about 70:1. I did some math and that it looks it should be 0.88 parts straw to 1 part coffee ground to get a 30:1 mixture, or 0.39 parts straw to 1 part coffee grounds to get a 25:1 mixture.

The problem is that they're such different shapes/densities/water content that it seems impossible to know how to get that ratio by measuring volumes. So I'd like to figure out how to adjust the ammt of straw to add by judging symptoms.

What are the symptoms of too much green and too much brown?

My compost is sometimes hot but usually just warm. It usually smells good. There have been a lot of bugs in the bottom third of it the last couple times I've turned it.

There's also been a whole lot of flies recently, mostly little fruit-fly things. I've been collecting kitchen scraps in a closed bucket and burying them in the middle to combat them, but there's still a lot of flies. I wonder if they are growing in the coffee grounds but they're so small it's hard to tell.

Anyway that's my compost. Any suggestions for how to heat it up and deter flies welcome. Any suggestions for getting the green/brown ratio right in general also welcome.

Thanks!

Comments (12)

  • Lloyd
    9 years ago

    I wish I could help you but I've not had a lot of success using straw as my sole carbon material.

    By your description of heat and no offensive smell I'd hazard a guess that you've got the C:N pretty close to where it should be.

    Lloyd

  • sylviatexas1
    9 years ago

    If it's warm & it smells good, I wouldn't worry about it.

  • davids10 z7a nv.
    9 years ago

    as an extremely successful composter i have to say i don't understand the obsession with green/brown percentages.

  • Kimmsr
    9 years ago

    At one time classifying Nitrogen as a "green" and Carbons as "browns" was supposed to help people keep things in balance. However, people have begun to fixate too much on that simple method and seem to have forgotten what each was supposed to represent, and good sources of Nitrogen are also brown in color (coffee grounds and manures) which helps confuse.
    If a compost pile has too much Nitrogen there will be an odor of ammonia present. If the compost pile has too much Carbon in relation to Nitrogen the bacteria will not have enough food to work hard enough to generate heat, but that could also be true if the moisture level is not adequate. A moisture level too high will displace the air the bacteria need to work and other, less desirable (anaerobic) bacteria will go to work and produce putrid (kind of sewage like) odors.
    Getting the C:N ratio close to that optimal 30:1 is the tricky part of the process and having an idea of which material is an N and which is a C does help but should not be such that it creates headaches in trying to determine what goes into the compost pile. It will all become compost, eventually.

  • armoured
    9 years ago

    I think kimmsr's input is exactly right on.

    As for fruit flies: you're basically doing the write thing by burying them. A few more things you can do are spread them out a little bit more, chop them finer to get quicker decomposition, and have a layer of something dry and brown on top, like shredded paper or cardboard. I'm sure there are other solutions too, just my suggestion.

    Or you can just live with it. Fruit flies don;t really cause any harm that I can tell.

  • Kimmsr
    9 years ago

    What some people describe as "fruit flies" in a compost pile are most likely fungus gnats that hatch out and grow in places with high levels of organic matter (a compost pile) that is too wet.
    Too much moisture will also stop the aerobic bacteria, that are the ones that generate heat, from working and allows the anaerobic bacteria to work instead which can produce off putting smells, often a sewage like, putrid, odor. So, if there are small fly like thingys buzzing around the compost that is an indication the material is too wet.

  • toxcrusadr
    9 years ago

    I have nothing substantial to add to the replies above on your question. Just wanted to mention, since you are getting a steady supply of those coffee grounds, do start a new pile every few months and allow the last one to cool, cure and finish. Maybe you are already doing that since there is apparently a pile of fine dark brown treasure showing on the right side of the frame. :-]

    This post was edited by toxcrusadr on Wed, Dec 17, 14 at 10:42

  • nexev - Zone 8b
    9 years ago

    Guessing by the looks of your boxes in the photos above it looks like they might be a little small. A larger pile will generate and hold more heat up to a limit where the pile can no longer get enough air into it though turning can help with that.

  • bensmithmath
    Original Author
    9 years ago

    Nexev, the photo is of two halves of a single bin. I made it according to these plans: http://www.vegetable-gardening-with-lorraine.com/homemade-compost-bin.html. The second pile is in another 4-layer bin. They seem to be working quite well so far.

    It has been raining like crazy lately and it definitely is too wet and will be for a while. The good news is that cold weather came with the rain and that seems to have suppressed the flies. Or maybe they're just resting. Or maybe since I've been burying the kitchen scraps and putting a layer of straw on top they've been starving for fruit if they're fruit flies.

    Anyway it sounds like my green/brown mix is fine, or maybe a little on the brown side. It was probably too wet before the rain from me watering it too much which was also encouraging the flies.

    Lloyd, I see why you don't like only straw. The compost is pretty stringy even when it's done; I don't know if that's a good thing or a bad thing. It maybe burns a little slow too.

    Thanks for the help, all!

  • toxcrusadr
    9 years ago

    Hot compost is great but always remember it doesn't have to be hot to get wonderful compost. When you're in heavy soil improvement mode and you have the materials, by all means. Just remember cold and slow is OK too, and 'a little heavy on the browns' is fine for that. It all leads back to compost eventually.

    Happy rotting!

  • MrClint
    9 years ago

    I'm going to throw in with Nexev. If you went with at least a 3' x 3' bin you would have a much greater margin for error. Overall design, brown/green ratios, keeping adequate moisture and heat levels are less problematic with a larger sized bin. Composting becomes dead simple. Plus you will have faster turnover, and then you can use your smaller bins as temporary storage or for final finishing.

    I crank out a lot of compost from this 3' x 3' bin:

    This post was edited by mrclint on Sun, Dec 21, 14 at 13:21

  • toxcrusadr
    9 years ago

    And if you make TWO of those, you can have one batch finishing and one bin for fresh material. :-]