It’s not particularly difficult to compost a bicycle, but there are certain special compost heap designs that favour the process. Obviously this can be a very slow form of composting and so it’s important not to rush the process since partially composted bicycles can make the formation of a fine tilth for seed sowing very difficult. The easy ingress of air and rainwater is known to favour rusting, and of course the addition of iron to the soil is of some benefit to maintaining colour in hydrangeas. The impact of aluminium and rubber is less well, known but leather saddles are favoured by some species of worm.
Fortunately most dedicated allotmeteers have innumerable old wooden pallets lying around awaiting a purpose and so I have photographed a number of suitable designs below. Please note in the above illustration that the bicycle tyres have been deflated for safety reasons.
Bicycles also make excellent supports for summer displays of bindweed.