Autumn leaves are mainly broken down by the slow action of fungi rather than by bacteria that decompose other compost bin ingredients quickly, so it’s best to compost them separately in a simple heap. To stop the leaves blowing away, it’s best to create a cage for them.
The leaves of all deciduous trees make good leaf mould. Small thin leaves such as birch break down fairly quickly, while large leathery ones such as chestnut benefit from being shredded first. Evergreen leaves and conifer needles take far longer to rot and should not be included in great quantities, and then only when chopped.
After a year, the leaves will have only half rotted, but will break up easily when handled. They can be used for soil improvement or for mulching around shrubs, where they will continue to rot down in situ. After two years most will have turned into fine, dark leaf mould. Use it as a seed-sowing medium or mixed with equal parts of fine garden compost, loam and sharp sand for potting.
Before you build your leaf heap, choose a position that’s out of sight but easy to access. It should be shaded in summer but not too sheltered from the rain.
Although no stirring or turning is strictly necessary, after a few months, it’s worth incorporating any still-dry leaves into the damper middle.