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Composting fish scraps

Posted by josko Cape Cod (My Page) on
Thu, Dec 24, 09 at 11:12

I can get all the fish scrap I can use and am wondering how and whether I dare compost it. I'd use a bin made of pallets with another pallet for the top, and could line the inside with plywood if that's appropriate.
The fish scrap comes in 5 gal buckets (~30 lbs), and I'm planning to layer it with sawdust, jointer shavings or wood chips. I've read fish scrap(heads, racks, skins and guts) has a ~6:1 C:N ratio. so I'd add 4 times the wood chips by weight.

So It would seem I should layer the carbon with (bucket at a time) fish scrap (keeping fish away from bin walls), proceed until I get to the top of the pallet bin, wet it all down, cover with a pallet, and hope for the best. Would I want to turn this pile?
I don't have to worry about animals getting at the stuff, but am very concerned about odors. A few years back, I tried a ~60 lb chunk of shark meat in a similar bin, and the putrid odor brought over the health department.

So, what's the best way to do this, given the goal is to compost a maximum amount of fish scrap but not have an offensive odor.
Thanks in advance.

Follow-Up Postings:

RE: Composting fish scraps

So long as it set long enough before turning and use the amount of sawdust that's appropriate to your application I don't believe it'd be a problem. Sawdust is very good at absorbing the odor. I have no practical experience composting that much fish, but it sounds like it would work.

RE: Composting fish scraps

  • Posted by paulns NS zone 6a (My Page) on
    Thu, Dec 24, 09 at 13:21

If it doesn't all freeze until spring, or at least go very slow.. How cold does it get there?

Aside from that your strategy sounds good, except for a couple of points. Fish scraps dissolve quickly, while wood chips are a very stubborn carbon - they don't make a good mix. Fine sawdust would be better - absorbent of moisture and odours, and a better way to capture nitrogen. I like to spread fish scraps as thinly as possible and if really concerned about odour, dust them thickly with soil or finished compost, which are both good deodorants.

RE: Composting fish scraps

  • Posted by pt03 3 Southern Manitoba (My Page) on
    Thu, Dec 24, 09 at 13:47

I think your plan is generally sound but I wouldn't use the plywood.

If I were to try doing large quantities of fish, I'd use sawdust on the bottom (3-4 inches), shredded leaves around and mixed in with the fish parts in a 6:1 ratio by volume. To top it off, I'd put another layer of sawdust (again 3-4 inches) topped off with a few inches of semi-finished 'post and covered with some cardboard. As stated by the OP, moisten as you go but don't moisten the top layer of sawdust or 'post during construction

Add some moisture to the top but under the cardboard after about a month or so and then once in a while after that. Let it sit for a year before I 'opened' it.

This would be an experiment because I've never 'done' fish.


RE: Composting fish scraps

Go for it.
Softwood dust is best no chips/shavings, but layer shredded leaves if possible due to massive cellulose/lignin in wood. Better using volume, not weight. 40:1 maximum mix. Assuming the fish scraps are fresh, not anaerobic/aged but 3 days in liquid is not harmful and should be pre-smelly.
DO innoculate every 2nd layer with good quality freshly-finished compost.
Consider less sawdust, substitute some fine-crushed charcoal for odor control, but don't overdo the charcoal.
But too much carbon-to-nitrogen will slow down decomposition drastically, and pile probably wouldn't won't heat past 95F. Exponential reproduction of thermophilic microbes is the goal, to produce heat. 150F is target heat, possible in 5 days if C:N is on target.
1/2-3/4" sawdust, 1.5"- 2" shredded leaves, one bucket of scraps with a sprinkle of compost, 1" hay/straw. Water.
Make the pile as fast as you can, collect the runoff (leachate) and put it back on the pile. Do not allow runoff to drainage ditches or other water sources.
Cover top with 1/8" layer of finely-crused (sifted) charcoal and 4"+ of clean hay/straw (square bale) to mediate rainfall/odor.
Fish scraps are not a 'chunk'. Surface area is important.
Mix each layer with garden rake, then water (no chlorine) EVERY layer. Entire pile must be very moist.

If it were MY pile, I'd use plywood walls (insulation is important in your neck'o the woods), 2-compartment bin, framed section of chain-link for the top & cover when cold/snowy (if it freezes, decay stops but will 'fire up' again when warmer), 3/4" plywood slats for front to keep out critters. Use a garbage can (tub) with one bucket of fish, 1/4 bucket of sawdust/chips, 3/4 bucket of finely-shredded leaves, 1/4 bucket horse manure, 1/2 bucket rainwater, 1 shovel of finished compost, well-chopped (shovel/bucket method) kitchen/table scraps when available, mix thoroughly until water is absorbed, add more water if needed, then layer the tight 'slurry' on 1.5" of shredded leaves or hay/straw, cover with 1" of hay/straw, water into leaves with a very light sprinkle of charcoal which means don't expect a pile temperature of over 145F - but must attain 131F in center within 9 days (or turn & add 1/2 bucket of more fish or horse manure to each 4" turned layer). Scalp pile on forked turns.
Use a compost thermometer and turn the pile through a section of chain-link fence when below 120F (mixing/aerating is important) or every 2 weeks but no sooner.

Doing it is how you learn.
Ask questions, make decisions and DO. Find an experienced local composter to help you. See/touch/smell is key and nobody can do that via email or post.
If you're gutsy, let the health inspector know what you're gonna do and ask for his/her advice. Teach 'em something.


RE: Composting fish scraps

Thanks folks. I should have said I'd do this in April or so, when it warms up. Meanwhile, I'll stockpile ~500 lbs of scraps (in a freezer) and a ton or so of sawdust. (I'm afraid some of that'll have to be jointer/planer shavings.)
I posted this now 'cause I need to start hoarding the stuff now to do this in springtime.

Thanks for the advice, and let's hope for the best (no stink).

RE: Composting fish scraps

  • Posted by pt03 3 Southern Manitoba (My Page) on
    Thu, Dec 24, 09 at 17:22

Josko, are you able to take some pictures as you build the pile? I'd like to see the process if you can.



RE: Composting fish scraps

Is there some reason why a person can't dig a pit and "build" a composte "pile" in the pit? It seems that this would take care of the smell factor and animals digging in the pile ... just cover with a "lid" of wood and lift each time you toss in new stuff.

There must be some reason why this method isn't used .... besides the hassle of digging the pit.... Oh I know ... there wouldn't be enough air to aid the composting critters in their appointed task .... is that it?

Oh well, another great idea bites the dust.....

RE: Composting fish scraps

A few years before buying our city house, followed by ownership of our current island property, we lived on a plot of rural land (rural by our Atlantic Ocean island standards, that is) - which was used by a fisherman tenant for his vegetable gardens. The fisherman's former garden was the site of our first real vegetable garden, and an unequalled inspiration for several gardens that followed.

When my wife and I had the pleasure to meet this fisherman, a year after our very productive first growing season, we exclaimed how fertile the soil was - as evidenced by how large and plentiful our harvest was.

He then went into a very colorful description of what he did to amend the soil. After returning from offshore fishing trips and processing his catch, he would haul the fish scraps to a dug pit by his garden and cover the load with layers of soil and compost. After a few days, he said you could actually see the ground undulating by the movement of organisms feeding on the sea scraps buried there. After each harvest, he would add the pit's contents to his gardens and then again in the spring. This went on for several years until we took over as stewards.

I have never had such a productive garden as the one nurtured by that fisherman.

RE: Composting fish scraps

  • Posted by paulns NS zone 6a (My Page) on
    Thu, Dec 24, 09 at 21:19

Fishermen tell stories like that here too. They used to bury whole dogfish in their gardens - a good use for those nasty things. Codfish guts as well. I wonder they didn't get foxes digging them back up.

Wow Soilguy that's a high-maintenance method you describe. I layer fish into piles all the time and turn only if it gets anaerobic, say from too much water (rain).

No sense watering the pile and then have to collect leachate. Fish scraps have a lot of water in them. 'Damp as a wrung out sponge' applies as usual. The trick is to capture as much of that fertilizer value as possible, not let it drain away.

Also, you say 'softwood dust' is best. I used to think so, then saw a chart from a reputable source in the Humanure handbook - I can find it if you like - where it shows hardwood sawdust actually breaks down quicker.

RE: Composting fish scraps

We were told the story in grade school history of how the Native Americans put a small fish under each hill when planting corn. Did the Native Americans have a problem with stray cats? If, indeed there were any truth or reason for the story, wouldn't scraps of fish work just as well as a small fish?

RE: Composting fish scraps

albert I have buried fish cleanings in the garden for years and plants love it, but in the volume josko is talking composting would make less work/digging. josko please let us know how you turn out. Here in Minnesota it is illegal to return fish or dump fish scrap into a lake. I am seeing a good service in composting for some of our resorts here.
I don't know how to link on here but Google[ fish waste composting Cornell] they have a tape for composting fish (you probably know that).

Curt :-)

RE: Composting fish scraps

The poster did not mention anything about the size of his yard, and neighbors; a very important consideration.

Fish are a minor ingredient in my piles; always put in the core at a temp of 130F or higher. Since my family has a fishing lake, I've read a bit on fish composting.

"The Seafood Waste Management Bibliography"
by Ken Hilderbrand

lists dozens of fish composting articles.

Two I have read are:
Composting Fish Waste An Alternative for Minnesota Resorts
Minnesota Sea Grant College Program 16 pages

The Compost Solution to Dockside Fish Wastes. University
of Wisconsin Sea Grant Instiute. 1989 19 pages

The info I've read uses wood chips over a very fine material like sawdust as a bulking agent.

Point of clarification

I previously wrote:

The info I've read uses wood chips over a very fine material like sawdust as a bulking agent.

a better way of expressing myself would be:

The info I've read uses wood chips RATHER THAN a very fine material like sawdust as a bulking agent.

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