Improved Worm Bin

For the past couple of years our family has been using a worm bin for composting food scraps. A growing population of red wriggler worms happily gobbles up potato peels, coffee grounds and apple cores. They don't get any meat, dairy products or citrus fruits, but they turn just about everything else into rich, dark compost that's ideal for gardening.

Our worm bin has been working very well, but there's a problem when the bin gets full-- it hasn't been easy to separate the worms from the compost. I've tried adding new food scraps to only one side of the bin, but the worms still like to hang out all throughout the bin. I've tried putting the compost out on a tarp and separating the worms by hand, but that takes forever!

Meditating on the lives of red wrigglers, I came up with the method described below and found that it works great.

Availability of plastic worm bins

Our old worm bit consisted of a wooden box with a hinged lid. After being outdoors for two years, the untreated wood began to decompose. So I decided to try a plastic bin. A large "Worm Barn" made from recycled plastic is available from Recycled Plastics Marketing (RPM) in Redmond, WA. The bin is 24" wide, 36" long and 18" high. It can hold 7.35 cubic feet of material.

Theory behind the worm separator screen

We know two things about red wriggler worms: (1) They like cool, moist, dark spaces where there is lots of vegetable matter to eat. (2) They don't like sunlight at all. When exposed to light, they skedaddle off into the darkness.

So if we want to persuade them to leave the compost in which they have been living, we expose a layer of the worm filled compost to sunlight, while at the same time providing them with an attractive place to go. That place is a mat of shredded newspaper moistened with the drippings from their compost home. We assume they are attracted to their food by smelling or tasting it in some way, probably via the moisture in the food.

How to build a worm separator screen

The key component of the separator screen is plastic mesh with a hole size of about 1/4". I originally purchased some wire mesh screen, but then after thinking about, I decided that the worms may not like to be in contact with metal. Aren't copper strips used to repel slugs? I figured the red wrigglers would be happier with recycled plastic than with galvanized steel.

You need to build a frame for the screen and here again, plastic lumber is better than wood, because it will last a lot longer in the wet environment of the worm bin. Plastic lumber and plastic mesh are both available from the same company that makes the "Worm Barn," RPM. You will need 10 linear feet of 1.5" x 1.5" stock. Plastic mesh comes in rolls 31" wide and 9 ft long for about $15.

There is a ledge in the Worm Barn about halfway up the side. The screen, with dimensions 24" x 35.5" rests on the ledge. The plastic lumber can be cut with ordinary tools for wood. Use 2" deck screws and predrilled pilot holes to fasten the frame together. The plastic mesh can be attached to the frame using 3/4" sheet metal screws with washers.

How to Separate Worms from Compost

	Here is the plastic worm bin with the completed worm separator screen.
	When you are ready to harvest the compost your worms have been producing, have ready a stack of newspapers and some fresh food scraps. You will need to tear the newspaper into strips. Paper from a shredder also works well.
	Add the torn newspaper and shredded paper to the bin and top it off with food scraps. The empty bin is quite large. You can either fill it with a large amount of paper, or you can temporarily place an empty low cardboard box in the bottom before you add the paper, so you won't have to tear up quite so much paper. You need to fill up the bottom section up to the ledge midway up the bin. Remove the temporary cardboard box after you have completed separating the worms.
	Place the separator screen on the ledge in the bin. Be sure it presses against the newspaper, so the worms will find an easy time sliding into the paper.
	Using a garden trowel, gently place the compost containing the worms onto the separator screen. Make a layer no more than 2" deep. Using a garden hose, gently spray some water over the compost. A sweet smelling liquid will moisten the newspaper, just the kind of scent that will attract your worms away from the compost.
	These red wigglers are saying, "Yikes! It's too bright up here. Let's head on down into the darkness below." Once inside the newspaper, they're thinking, "Hey, not bad! There is lots of food here, and it smells just like home!" In only about 20 minutes, most of the worms will have figured out that they should crawl down into the newspaper. You might find a few slow pokes, so give the dawdlers another 10 minutes.
	After a half hour, carefully scoop up the compost from the screen and start collecting it. Add another layer of compost from your original pile and repeat the process until you've harvested all your compost.
	In a mere two hours, all the worms are in the bin with the newspaper and new batch of food scraps, ready to work for another year. And you have a big pile of compost ready to use with your tomato plants.
	You will observe that your tomato plants grow like crazy with the compost from your worm bin. They love it!