How to make your own worm composter

There are plenty of worm composter models on the market, but you can easily make one yourself, at low cost, with a few plastic bins and a little DIY. Here's how to do it, step by step.

What you'll need

The project starts with a set of stackable or nesting bins — plastic, wood, or polystyrene — which are easy to find at hardware stores. You'll need at least four: two bins to serve as composting trays, one bin to collect the worm tea, and a final one to raise the whole unit off the ground. You'll also need a lid to close the top.

As for size, bins measuring about 11 x 8.7 in (28 x 22 cm) and 6.3 in (16 cm) deep are right for a household of 2 to 3 people — the same guideline as for a store-bought model, as we explain in our guide The tray worm composter. For a larger volume of food scraps, add more bins or choose a larger surface area, keeping to a maximum depth of 7.9 in (20 cm) per bin. Also make sure the gap between the stacked bins stays small, to limit fruit flies getting in.

Building steps

STEP 1

Passage holes

STEP 2

Ventilation holes

STEP 3

Cover the handles

STEP 4

Install the spigot

STEP 5

Riser bin

Step 1 — Drill the passage holes. Draw lines 0.6–0.8 in (1.5–2 cm) apart on the bottom of the two composting bins. Use the points where the lines cross as guides for drilling 0.2 in (5 mm) holes: these let the worms move from one bin to the next, just like in a store-bought tray model.

Step 2 — Drill the ventilation holes. Drill small holes about 0.04 in (1 mm) wide along the sides of the composting bins and in the lid. They let air circulate inside the worm composter while staying small enough to keep fruit flies out.

Step 3 — Cover the open handles. If the bins you've chosen have open handles, you'll need to seal them — with non-biodegradable fabric and wire, a piece of aluminum angle, or any other material that suits your type of bin. Just make sure the bins still nest properly inside one another.

Step 4 — Install the leachate spigot. Drill a hole in the bin meant for collecting the worm tea and install a spigot — easy to find at garden centers or hardware stores, or for sale right here ;) — to control the flow of liquid into a container placed underneath. Don't forget to add a rubber gasket to prevent leaks.

Step 5 — Prepare the riser bin. Cut an opening in the bin used to raise the unit so the container collecting the worm tea can slide in easily. Don't cut the plastic all the way to the bottom: that way, any leak stays contained inside the bin instead of running onto the floor.

Key takeaways

Once these five steps are done, your homemade worm composter is ready to use: all that's left is to add the bedding and your first worms.

A wooden version, just as effective

Wood is a great alternative to plastic for building your worm bin. It breathes better and naturally absorbs some of the moisture, which makes it easier to manage moisture levels day to day. On the other hand, it breaks down faster than a plastic bin — expect two to three years of continuous use from an untreated wooden box, longer if you let it dry out for a few days between bedding changes, or if you apply a non-toxic waterproof finish (polyurethane varnish, for example) to the edges. Avoid pressure-treated lumber, though: the preservatives it contains (based on copper, chromium, or arsenic) are toxic to worms and to the environment alike.

A simple box made from boards or exterior plywood is all you need: drill two rows of holes about 1 in (25 mm) wide in the sides, one near the bottom (2–3.1 in, or 5–8 cm, above the base) and another near the top to let warm air escape. You can staple fine mesh over these holes to keep the contents from spilling out. For two people, a base of about 23.6 x 23.6 in (60 x 60 cm) and 7.9 in (20 cm) high is enough; for a larger household, a roomier box of around 11.8 x 23.6 x 35.4 in (30 x 60 x 90 cm) works better. Budget between €30 and €45 for materials, screws included.

What's next?

A homemade worm composter works exactly like a store-bought model: worms move between the bins the same way, and you collect worm tea through the spigot just the same. Head over to our guides Which type of worms should you use in your worm composter? and How to start your worm composter for the next steps.

Build or buy: which is right for you?

Building your own worm composter lowers the upfront cost and lets you reuse bins you already have at home. On the other hand, it takes a bit of time and DIY, plus extra care with watertightness and hole size — two things a store-bought model has already calibrated and tested. If you'd rather have a ready-to-use solution, browse our full range of worm composters.

Did you know?

Building your own worm composter is by no means a must: it's an affordable and rewarding option for anyone who enjoys DIY, but a store-bought model is just as effective and saves you time.

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