An improved compost bin is disclosed and a ventilation channel is formed directly beneath the compost contained in the bin. A tunnel member having a perforated upper portion is contained in the channel to maintain a free passage for air to the base of the heap. The tunnel also prevents the walls of the channel from collapsing and the passage thereby becoming blocked either by the substrate on which the bin is mounted on by decomposing vegetable matter from the bin.In preferred embodiments, end caps are provided to further inhibit the encroachment of the substrate around the walls of and into the tunnel. Holes are provided in a central portion of each end caps to ensure free passage of air.The bin comprises a plurality of similar panels which interengage to form a plurality of vertical sliding joints. The dimensions of the panels and the tunnel are preferably such that, when not in use, the panels may be confined within the tunnel. The bin is normally sold in a kit taking this form. End caps, where used close the tunnel and auxiliary elements such as locking pins and a cover may thus be contained in the package.