The Schwartz's Flow-Through Vermicompost Barrel
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Created: September 2, 2012 | Last updated: May 30, 2015

About a year ago, I purchased two large plastic barrels someone had posted on Craigslist. I used one for a rain barrel and the other sat in my garage waiting for a project. I recently came across instructions for building a tumbling composter out of a barrel and thought that this would be a great use for the barrel, since my old compost bin was not in great shape. Except, I wanted a design that would keep the input material and finished compost separate.

I came up with the idea of a grate that would hold the input material but let the finished compost slip through for convenient use. Some research revealed that this type of design was already well-known in the vermicomposting world and referred to as a flow-through composter. I got excited to try keeping worms again. Little-known fact: My old compost bin started out as a vermicompost bin, but the worms very quickly fled; I hadn't put much thought into the design and so I suppose it was not very comfortable for them.

I looked at the various ways other folks had built flow-through bins, came up with my own plan, and headed off to the hardware store. It took me about seven hours of work to complete construction.

I will update this page with additional details as the bin is used.

1 barrel
3 2" plastic drain covers or louvered vents
4 exterior hinges
1 exterior latch
30' " inside diameter (ID) PVC pipes
26 matching PVC pipe end caps
1 drain
2 cinder blocks or other suitable platform
Drill and assorted bits (suggest Forstner bits)
Phillips-head screwdriver
Saw(s) suitable for cutting barrel and pipe
Measuring tape
Permanent marker
Water and soap for cleaning barrel

Barrel with suppliesI wanted to have a drain so that I could collect any leachate that might seep out. I used a kitchen sink drain because I thought it would best funnel the liquid to my collection bucket.

I cut the hole for the drain without much consideration for the inside of the bottom of the barrel and ended up cutting it in the worst possible location. The shape of the barrel there was uneven and so the drain could not be flush against the bottom and I fear it will leak.

The choice of drain may or may not have been a good idea. I'll update this page with more information on how well the drain worked otherwise. (Turns out a drain isn't really necessary, see update at bottom of page).

I used string to help mark straight lines on the curve of the barrel to be cut.

I oriented the grate pipes perpendicular to the access panels because I thought it might make it easier to rake the compost from below if needed to loosen it.

Barrel with holesWhen drilling holes for the grate pipes, I started with one along the seam of the barrel so that it would be easy to make the other one exactly opposite. I tested the pipe, cut it to size, and labeled it with a "C". I then worked outward, making two holes on each side of the center one, cutting the pipe, and marking it so I knew which spot it went in. This worked really well.

Drilling the outside few holes was a bit difficult because they had to be cut at a relatively large angle to the side of the barrel in order to reach the corresponding hole. For the final few, I had to go back and widen the holes a bit to make them reach. I also found that sitting on the barrel could deflect the sides and make it easier to get the pipe through the holes.

The pipes had a ⅞" outside diameter (OD) and I spaced them roughly that far apart.

I cut each of the pipes about 1" longer than necessary so that I could try to push-pull them as a method of loosening finished compost. (This is really helpful, see update at bottom of page).

Finished compost retrieval hatch I sized the finished compost retrieval hatch to the size of the shovel I plan to use to gather the compost.

I lined the grate with newspapers and added some dirt, leaves, compostable materials, and red wiggler worms.

Completed barrel     Completed barrel

 Numbered pipes     With compost!

Barrel and catalog model

Update May 30, 2015: I have used this composter for several years and it continues to serve me well. The only real issue is that the door to the harvesting hatch very quickly warped and does not close, so I removed it. Also, the drain I installed doesn't really matter, there is no excess of water that needs to drain so just skip that if you build one of these. On the plus side, making the PVC pipes a little long was a good idea, as moving them back and forth a couple of times helps dislodge loose compost near the bottom when I'm ready to harvest.My worms have survived several hot summers and freezing winters and produced a heck of a lot of great compost.