How to Build a Worm Farm with Polystyrene Foam Broccoli Boxes

If you would like to try worm farming without buying a commercial worm farm, a simple system can be built from two recycled polystyrene foam broccoli boxes. These boxes are light, reasonably well insulated and large enough to make a useful small worm farm.

The design is very simple. One box forms the upper worm chamber, which holds the bedding, worms and food scraps. A second box sits underneath and catches any excess liquid draining from the upper box. With the boxes collected beforehand, construction only takes a short time and requires very few tools.

What You Will Need

To build the worm farm, you will need:

1. Two matching polystyrene foam broccoli boxes with lids. Only one lid will be used.
2. A piece of plastic shade cloth larger than the inside base of one box, with enough extra material to extend partway up the sides.
3. Several sheets of newspaper to line the bottom of the upper box, plus additional newspaper to use as a damp worm blanket.
4. A short length of 12 mm (1/2″) black polyethylene irrigation pipe, or another narrow plastic tube of similar size, approximately 20 cm (8″) long.
5. No. 1 and No. 2 Phillips-head screwdrivers for making the ventilation and drainage holes.
6. Bricks, concrete blocks or other sturdy supports to raise the worm farm above the ground.
7. A small bucket or container to place beneath the drainage pipe.
8. Coconut coir or another suitable worm-bedding material.
9. Composting worms such as red wrigglers or tiger worms.

Basic Worm Farm Layout

The diagram below illustrates the basic design of the worm farm and how the two boxes work together.

The two-box design separates the worm chamber from the drainage chamber. The upper box contains the worms, bedding and food scraps, while the lower box remains empty and catches any excess moisture that passes through holes in the base of the upper box.

The upper box also needs ventilation because the worms and the microorganisms that break down the food scraps require oxygen. The bedding therefore needs to remain damp but loose and well aerated. If it becomes saturated with water, the spaces that normally contain air fill with water instead, which makes the bedding poorly aerated and unsuitable for the worms.

The lower box is not intended to hold bedding or worms. Its only job is to collect excess drainage and direct it through the outlet pipe into a container underneath.

Worm Farm Construction, Step by Step

Step 1 – Prepare the Two Boxes

Take two matching polystyrene foam broccoli boxes. One will become the upper worm chamber and the other the lower drainage chamber. Only one lid is required for the finished worm farm, so put the second lid aside.

Step 2 – Make Drainage Holes in the Upper Box

Turn the box that will become the upper worm chamber upside down. Using the No. 2 Phillips-head screwdriver, punch two rows of drainage holes through the bottom of the box and space them reasonably evenly across the base so that excess moisture can drain from different parts of the bedding.

Push the screwdriver from the outside of the box towards the inside. Polystyrene tends to break away slightly where the screwdriver emerges, so working in this direction leaves the visible outside surface of the box neater.

These holes are only there to allow excess moisture to escape. A correctly managed worm farm should remain damp without having water continually flowing through it.

Step 3 – Install the Shade-Cloth Liner

Cut a piece of plastic shade cloth larger than the inside base of the upper box. Lay it over the bottom so that it completely covers the drainage holes and extends partway up the sides.

The shade cloth allows water to pass through while preventing loose bedding from falling through the drainage holes into the lower box. It also makes it more difficult for the worms to move through the holes.

Step 4 – Add the Newspaper Liner

Lay several sheets of ordinary newspaper over the shade cloth and overlap or fold them as necessary so that they cover the bottom of the box.

The newspaper provides an additional temporary barrier beneath the bedding. It will eventually soften and decompose, but by that stage the bedding above it will have settled together and the shade cloth underneath will remain in place.

Step 5 – Make Ventilation Holes in the Lid

Take one of the polystyrene lids and use the smaller No. 1 Phillips-head screwdriver to make two rows of ventilation holes. Space the holes evenly across the lid so that air can enter over a broad area rather than through only one part of the box.

As with the drainage holes, push the screwdriver from the outside surface towards the inside. This keeps most of the rough broken polystyrene on the inside of the lid where it will not be visible.

The lid keeps the inside of the worm farm dark and sheltered while the holes allow fresh air to enter. Worms need moisture, but they also depend on oxygen reaching the moist bedding, so ventilation is an essential part of the design.

Step 6 – Prepare the Worm Bedding

If you are using a compressed coconut coir block, place it in a bucket and add water until it has absorbed enough moisture to expand fully. Break the softened coir apart by hand and fluff it up so that it remains loose rather than packed tightly together.

The bedding should be thoroughly damp but not waterlogged. When squeezed firmly in the hand, it should feel similar to a wrung-out sponge rather than releasing a stream of water. Loose, damp bedding holds the moisture the worms need while still leaving spaces between the particles for air.

Coconut coir works well because it absorbs water without collapsing into a dense mass. Shredded cardboard, shredded non-glossy paper, aged compost and other absorbent carbon-rich materials can also be used as worm bedding, either alone or mixed together.

Step 7 – Fit the Drainage Pipe to the Lower Box

Take the second polystyrene box, which will become the lower drainage chamber. Make a hole through one side of the box as close as practical to the level of the inside bottom.

Make the opening slightly smaller than the outside diameter of the 12 mm irrigation pipe so that the pipe fits tightly when pushed through the polystyrene. Insert approximately 5 cm (2″) of pipe into the box and leave the remainder projecting outside.

Positioning the pipe close to the bottom allows accumulated liquid to flow out rather than leaving a pool of water sitting in the lower box.

Step 8 – Raise the Lower Box

Place the lower box on bricks, concrete blocks or another stable support so that it is raised far enough above the ground to fit a small bucket or container beneath the drainage pipe. Make sure the supports are level and positioned securely because the completed worm farm will become much heavier once moist bedding and food scraps are added.

Place the collection container directly beneath the end of the pipe so that any excess drainage can be caught rather than spilling onto the ground.

Step 9 – Assemble the Worm Farm and Add the Bedding

Place the upper worm box directly on top of the lower drainage box, then add the prepared bedding to the upper box. Spread it evenly but do not press it down, because compacting the bedding squeezes out the air spaces that the worms need.

The bedding will gradually absorb moisture released from food scraps while providing a loose material through which the worms can move. Keeping it damp and open-textured is more important than making it perfectly level or tightly packed.

Step 10 – Add the Worms and Worm Blanket

Place the composting worms on top of the prepared bedding and allow them to move down into it. Cover the surface with several sheets of damp newspaper to form a simple worm blanket, then place the ventilated lid on the box.

The damp newspaper helps keep the surface beneath it moist and dark, while the lid protects the worm farm from light, drying winds and debris. The worm farm is now ready to begin receiving small amounts of food.

Where to Put the Worm Farm

Place the worm farm somewhere shaded and protected from direct sun, heavy rain and extreme temperatures. A shaded veranda, covered outdoor area, shed or garage can work well as long as the location has adequate airflow.

Polystyrene slows the movement of heat through the walls, but it cannot keep the contents cool if the box is left in strong summer sun. Because composting worms live close to the surface of decomposing organic matter, they cannot move deep into cool soil when the box overheats. A sheltered position therefore helps keep the temperature and moisture level much more stable.

Protection from heavy rain is also important. Rain entering through the ventilation holes can soak the bedding, fill the air spaces with water and cause large amounts of liquid to drain into the lower box.

What About the Liquid That Drains Out?

Most of the moisture entering a worm farm comes from the food itself. Fruit and vegetable scraps contain a high proportion of water, and some of that water is released as the scraps soften and decompose. When the bedding contains more moisture than it can hold while still remaining aerated, the excess moves downward through the drainage holes into the lower box.

The liquid that drains naturally from the bottom of a worm farm is called leachate. It is not the same thing as worm tea or vermicompost extract, which is deliberately made by mixing finished vermicompost with water.

A well-managed worm farm should remain damp rather than saturated and should not continually produce large quantities of leachate. If the collection container is filling quickly, the bedding is too wet. Stop adding extra water, reduce very wet food scraps for a while, and mix in some dry shredded cardboard or paper so that the excess moisture can be absorbed and the bedding becomes better aerated again.

Starting Your New Worm Farm

Begin feeding the worms with a small amount of chopped kitchen scraps rather than filling the box with food immediately. Bury the scraps beneath the bedding so that they remain in the moist zone where the worms are active and are less exposed to fruit flies and other insects.

Add more food as the previous material is broken down. If fresh scraps are added faster than the worms and decomposer microorganisms can process them, uneaten food accumulates, holds excess moisture and can begin to smell. Starting slowly allows the worm population and the biological activity in the bedding to build up together.

Continue to keep the bedding damp but not waterlogged, and replace the damp newspaper worm blanket when it becomes badly decomposed. For detailed information on feeding composting worms, maintaining the bedding, troubleshooting problems and harvesting worm castings, see The Complete Guide to Worm Farming, Vermicomposting Made Easy.

If you’d like to learn more about worm farming, please check out the following articles:

• The Complete Guide to Worm Farming, Vermicomposting Made Easy
• How To Build a Worm Tunnel In-ground Worm Farm
• Why You Shouldn’t Use Bleached or Glossy Paper in Your Compost or Worm Farm
• Why You Shouldn’t Use Sales Receipts in Your Compost or Worm Farm