when is compost "done"?

[LizzL]

Compost first timer here!
I've got a metal drum in which I keep my compost, mostly kitchen waste, veg and stuff, and garden waste. So when will I know it's "done"? When all the big bits are gone? can you just spread rotten stuff and plant stuff on it?

[gumbo2176]

Compost is done when it very much like loose soil. You mention it is in a metal barrel. Are there drain holes in the barrel? Can you turn the material over to get the stuff really mixed up to aid in decomposition? Are you keeping it moist to promote decomposition?


The problem with composting in an enclosed container is compost needs air flow to help it along properly. I just have mine on the ground in a corner of my yard. I'll move it from one spot to an adjacent area when it is properly broken down and add kitchen scraps, yard waste, plant material, coffee grounds etc. to the other pile and mix it in so it can start the process of becoming compost. I plan on building a proper compost bin one of these days with 2 bays====one for finished compost to be stored till needed and the other for the actual composting of material.

[rainbowgardener]

The trouble with composting in a barrel, along with getting enough air, is that it needs to be batch style composting. That is, you load the barrel up with a batch of stuff and then you don't keep adding more, just let the batch compost until it is finished. Otherwise if you keep adding more, you will always have an un-separatable mixture of finished and new stuff.

Finished is when it looks like dark rich earth with no identifiable ingredients in it and it smells just rich and earthy.

If you are just putting kitchen and garden wastes in, you probably really need to be adding some browns to get good compost. Read the Greens/ Browns sticky at the top of this Forum. The kitchen and garden wastes are mostly all greens (unless garden wastes includes fall leaves which are brown).

If you have unfinished stuff, you can spread it, or bury it in your garden. Spreading it without burying it seems a bit yucky... would look messy, maybe be a little smelly, and tend to attract critters to your garden that you may not want. But burying it next to your plants can sometimes actually pull nutrients away from the plants in the process of breaking down the unfinished stuff. If you have a garden bed you won't be using until spring, burying your unfinished compost there would be fine. By spring it will be all nicely broken down.

[Joyfirst]

You don't have to wait untill it is all nice and done to use it, especially if you use it on the bottom of the beds. I think it is pretty good to have it not cooked all the way, because it attracts worms and other life to the beds.

[toxcrusadr]

BTW, the composting process is basically the 'rusting' of organic matter, so to speak. It's a moist environment with organic acids and biological activity out the wazoo, all of which adds up to 'very corrosive' to regular steel. Your drum will become compost in short order. It won't hurt the compost, but you might want to plan for a different bin, you're going to need it.

[Toil]

doesn't the water and air rust the metal in an electrochemical process called oxydation?

bacterial processes, like the ones that do most of the work in hot compost, don't rely on acids to digest food, but rather, on enzymes. They are so small, they don't have room for openings, so everything has to be able to move through the cell wall. The whole process results in a net loss of hydrogen for the soil solution, not a gain. (as far as I know)

In other words aerobic bacterial action raises pH, but because you have iron, water, and air, you will get rust no matter what you do, short of immersion in water and installation of a sacrificial node that gives up ions easier than the barrel (which needs replacing as it melts).

[toxcrusadr]

Toil, I'm by no means an expert on biological processes, being a chemist rather than a biologist. I just thought I'd read in more than one place that a microbially active environment would enhance oxidative corrosion. One mechanism I can think of is that dissolved salts are much higher in compost than in rainwater or tap water, so the conductivity of the water phase is much higher. This would enhance already ongoing electrochemical rusting the same way salt water will rust your car faster than rain water.

Anecdotal evidence: many years ago I built a compost tumbler out of a steel drum. It rusted away in a couple of seasons. This was in the NM desert where cars and other metal items seem to last forever.

[Toil]

this could be an interesting experiment: one drum is kept moist, exposed to air, and sterile, while the other develops bio-slime.

which would rust first?

[toxcrusadr]

Here's a pretty technical article on microbially induced corrosion (MIC):

https://corrosion-doctors.org/Corrosion-Factors-Cells/corrosion-cells-microbial.htm

They actually form little electrochemical cells (batteries) that eat holes (pits) in metals. The composting environment is rich in moisture, oxygen, dissolved salts, organic acids and chelating agents, and loaded with microbes. I would think it is much more corrosive than typical topsoil.

More can be found by Googling "microbes and corrosion", "microbiologically induced corrosion", etc.

Off on a tangent again...I don't get to use my environmental chemistry very much these days!

[Toil]

ya but the point is paint your drum, right?


And thanks for the neat info, I did not know that. Is there anything microbes don't do?

[toxcrusadr]

That might work, if it's really good paint.

Microbes...yes they are versatile critters that make the world go round. I don't think they can balance the federal budget deficit though. They have been known to decide wars, but we're not allowed to use them for that anymore.

[Toil]

I was over at a house that received one of my bokashi bins when I moved out of my place. It was half full, and they find the smell so revolting that they have not opened it (I enjoy the smell). It's been pickling for months, and in the bucket I have an iron 5lb weight on top of everything. The kind you see in the gym.

Now this is an acidic environment. About the same as OJ and dominated by lactic acid bacteria. Anyway, the iron weight looks like it is slowly boiling away. There are these big, weird looking bubbles the color of scummy rust. It sure does look to me like the microbes are having that effect, but I have nothing to compare. The metal is quite moist, because the whole bucket stays sealed.

[toxcrusadr]

Interesting. I'm guessing a bokashi bin is a relatively low-oxygen environment, if the lid is kept on and it's fermenting (producing CO2). The iron is being oxidized to ferrous iron (Fe+2), which is soluble. When it hits air it becomes ferric iron (Fe+3) which combines with oxygen to make rust (iron oxide). High iron well water often has dissolved ferrous iron, since there's no air down there to oxidize it all the way to ferric. When the water hits the air it goes to ferric and you get rust stains on your tub.

Anyway I bet the bokashi leachate is pretty high in ferrous iron with that hunk of iron in there. Not necessarily a bad thing, just thinking out loud.

[Toil]

I imagine any leachate would be high as well, but this time I stumbled on perfect moisture levels and there is none.

I won't get it that way every time, so maybe I should put the weight on plastic... I wonder what effect all that iron could have... good point!

Right now the big bubbles are cool tho.

[toxcrusadr]

I don't know of any negative effects that would result from high iron in compost. It's a nutrient of course, and it's probably worse to have a deficiency. There would be a natural background level in soil as well. Unless someone chimes in with a problem, it's probably nothing to be concerned about.

[vermontkingdom]

Being as old biologist myself, I found this discussion to be both highly interesting and informative. thanks

[toxcrusadr]

Glad we didn't send *everybody* running/screaming from the geeky science discussion.

I sit at a desk being an environmental chemist bureaucrat all day. This forum gives me an outlet, especially since our net nanny system blocked the other one I used to hang out at...

[tedln]

Back to the original question about composting in a barrel. I used a plastic, 45 gallon drum with a 1" x 2" wire mesh in the bottom. I built a stand to sit it on and placed a catch basin under it to catch the finished compost dropping through the bottom. I ran a lot of organics through that thing during the hot summer and it worked well. My only complaint was the fact that it didn't produce much compost compared to the amount of organics that went through it. I decided that in order to produce large quantities of compost, I need a large compost pile. I started my pile this fall.

Ted

[Odd Duck]

To the OP, I had a master gardener/horticulturist once tell me the perfect way of telling when compost is ready.

When it doesn't gross you out to stick your bare hand in it!

Basically what everyone else has said - no odor except rich earth, not sticky but crumbly, very little identifiable - maybe a few twigs or a peach pit (throw that back in), NEVER whole chunks of any identifiable food (except those darn peach pits), nothing slimy, nothing really gross at all (and I mean that in the slang and the scientific sense).