All leaves and conifer needles will eventually break down into leafmould. Some leaves, such as oak, beech or hornbeam, break down with little assistance and produce an excellent quality product.
Thick leaves like sycamore, walnut, horse chestnut and sweet chestnut need to be shredded before adding to the leafmould pile, as they are much slower to break down. Alternatively, they can be added to the compost heap after shredding.
Evergreens such as holly, Aucuba and cherry laurel, are better shredded and added to the compost heap, where they will break down faster than if added to the leafmould pile.
Conifer needles will eventually break down, but may take two to three years to decay. Conifer hedge clippings are better added to the compost heap than used for making leafmould.
Pine needles are worth gathering and placing in a separate leafmould pile as they produce acidic leafmould, which is ideal for mulching ericaceous plants, such as rhododendrons, azaleas, camellias, Pieris and blueberries.