How to Build A Flow Through Worm Bin

This past weekend I decided to try something since I had the materials lying around to build a continuous flow worm bin system which in reality can be purchased for less than forty dollars.

I had seen a similar concept using metal rods as well as had the bottom left wide open, allowing for variety of varmints to enter the system. I decided to build it keeping it simple so as about anyone could put it together.

One thing to keep in mind is many web sites state that the end product is worm castings in a continuous flow through system. The reality is that the end result is a vermicompost, a mix of some unfinished decaying organic matter and worm castings. While the worm castings by themselves are considered “Black Gold”, the vermicompost will do very well in many garden plants too or simply screen the mixture.

Many ask if you will lose many worms out of the bottom, no worries here. As with anything you will lose a few stragglers however the worms are consistently migrating upwards and should reproduce much quicker than your few lost worms coming through the bottom when you harvest your vermicompost.

Materials / Tools:

1 – 55 Gallon drum (one not previously used for chemicals)

1 – 2’ X 2’ piece of 3/8” plywood if your bin has not lid

4 – strips of 3/8* plywood or less, can be from lid scrap above.

1 – 12” X 8” – 1/8” or ¼” galvanized hardware cloth

4 – Short wood screws ~ ¾” to 1”

40’ – Weed whacker line

1 – Piece of approx. 80 grit sandpaper

1 – Reciprocating saw

1 – Phillips or flat head screwdriver… depending on your screws.

1 – Cutting tool for the galvanized hardware cloth.

1 – tape measure.

1 – drill

1 – 1/8” drill bit

The first thing to do is mark out a 12” wide  by 8” high opening on the bottom, 2 inches from the bottom of the drum.

Next center and mark out another opening 10” wide by 6” high inside the one you just made.

Cut out the smaller opening first as this will make it much easier. Once you cut the outer opening, save this piece.

I ran the weed whacker line from side to side as I noticed the structural strength was weekend from front to back once the opening on the bottom was cut. Hence locate and center mark your two sides two inches above the top of your cut opening on the bottom of the drum.

Now you will want to drill holes 1 1/2” on center. This does not mean going around the exterior and measuring 1 ½” all around as this will mess you up.

The simplest way to figure this task out is to drill your two centered side holes, measure 1 ½” to either side and drill those two out. Temporarily run the weed whacker line through all three holes on both sides, back and forth and snug up a little. Now you can reach inside and lay the tape measure over the three lines you ran and mark out 1 ½” in both directions on both sides of the bin. Be sure your marks are level before proceeding to drill them out. You can use your tape measure or if you have scrap wood around, use a precut piece as a template to the height from the bottom of the drum to the height of the holes to be drilled.

To run the weed whacker line tie a large knot on one end of the line and begin threading the line back and forth, starting at either the front or back of the drum. Once ran, proceed to reach inside the drum and start by pulling and placing tension on the lines to snug up, beginning where you first began to thread the line. Once complete, tie another knot on the other end to secure the tension on the weed whacker line and cut off excess.

Now you can cut your lid for the drum if your drum did not come with one out of the 3/8” plywood. Be sure to leave it a little larger than the drum top to over hang a little to prevent rain… from getting in should you be placing outside.

Under the lid, Drill 1/8” holes around the top of the drum spaced about 1 ½” apart.

You should have enough scrap from the plywood lid to cut four strips. Cut four pieces six inches long, two at 1 ½” wide and two at 2” wide.

Use the sandpaper to sand the edges of your fron lower door panel to remove the burs left behind when cutting the door.

Trim the galvanized hardware cloth to fit by being a little smaller than the outer edge of the saved piece from your bottom opening cut. Use the wider strips on the front and the narrower strips on the back of each side to hold the galvanized hardware cloth in place, securing with the four screws. Line them up with the inside edge of the opening so as they over hand on the outer side, one by ½” the other by 1”. Always place the galvanized hardware cloth on over the face which will be facing outwards towards you when fitted into place.

Always start off the flow through system with six pieces of newspaper, add 4” to 6” pre soaked sphagnum peat moss (damp, not soaking wet) on top and begin adding food scraps.

To help maintain the pH level is to layer your green (i.e. vegetable scraps) and brown (i.e. shredded newspaper, cardboard) as well as add ground eggshells when available in moderation.

After two or three months, use a garden claw to lightly rake the underside of the weed whacker line from side to side to remove the finished vermicompost. This can then be performed weekly if the system is setup and functioning correctly.

Bruce