How to Build Your Own Compost Shredder

Composting is a very important to the gardening process.

Not only does composting promote ecological sustainability and reduce organic weight, but it also produces great fertilizer. By shredding the materials you want to compost, you can expedite a process that can take months and reduce it to a few days. Modifying a used lawn mower into a compost shredder is a great way to promote quick composting without breaking your budget.

Create a 4½ by 8½-inch opening in the deck of the mower, taking care that it is centered in front of the power plant.

Make a tapered hopper out of the sheet metal. It should measure 16 inches tall with a mouth that is 11½ by 13 inches and a 3-inch shield at the top. This part is also called the chute.

Bolt the chute over the deck opening using the two conduit braces by flattening and bending the ends of the braces, followed by bolting the supports so they are between the back of the hopper and the rear of the platform.

Fasten the small sprocket onto the shaft of the engine.

Place the old bike chain over the cogged wheels.

Mark a spot for the feed paddle shaft. This should be between the hopper's walls. Make sure that the marked area will leave enough room for a large sprocket to fit through it.

Securely bolt the floor flanges over the shaft marks.

Drill half-inch holes in the floor flanges for the paddle axle.

Fasten the chain wheel to the shaft, then slip the shaft into place.

Mark the shaft for drilling so it will securely stay in place.

Size the sheet metal to create feed paddles that can rotate without obstruction in the chute. Allow at least a half-inch clearance for all areas.

Measure and link the chain in place so that the guard is between the deck and the hopper.

Things You Will Need

  • Self-propelled rotary mower with a PTO shaft
  • Sheet metal
  • Old bike chain wheel
  • Old bike chain
  • Old bike guard
  • Small sprocket
  • 15-Inch piece of a ½-inch rod
  • 2 pipe floor flanges
  • 2 lengths of electrical metallic tubing, ½ inch by 25 inches
  • Assorted fastening hardware
  • Power drill
  • Marker
  • Welding tools
  • Safety goggles


  • Modifying a mower can be very dangerous if you don't have experience working with hardware or machinery. Consult your local hardware store for assistance or purchase a ready-made compost shredder if you are unsure of your abilities.
  • Do not take on this project if you don't have prior experience with modifying machinery. This is a very advanced project; if you do not know what you are doing you could get seriously injured.