What Should I Do with Autumn Leaves — Compost or Leaf Mould?

Autumn leaves are one of the most abundant garden composting materials, but they are better processed separately from the main compost heap rather than added to it in quantity. Leaves are very high in carbon and low in nitrogen, which means they decompose very slowly in a standard compost heap — they can take years to break down fully and may slow the decomposition of everything else. The better solution is to make leaf mould: a simple, separate process that produces one of the most useful soil amendments in the garden.

How to make leaf mould

Collect fallen leaves in autumn and pile them in a simple enclosure made from chicken wire fixed to four posts — or simply stuff them into large bin bags with a few holes pierced for ventilation. Pack them loosely, moisten if very dry, and leave them undisturbed. The leaves will break down slowly over one to two years into a dark, crumbly, earthy-smelling material — leaf mould. Shredding the leaves first (run a lawnmower over a pile of them) accelerates the process to six to twelve months. Oak, beech, and hornbeam leaves make the best leaf mould; avoid large quantities of walnut leaves which contain compounds inhibiting to plant growth.

Adding leaves to the compost heap

Small quantities of autumn leaves can go into the regular compost heap as "brown" (carbon) material — use them to layer between nitrogen-rich "greens" like kitchen scraps or grass clippings. Shredded leaves are better for this than whole ones. Keep the proportion of leaves in the main heap below about a third of the total volume for best results. If you have large quantities, leaf mould is a more efficient use of them.

Uses for finished leaf mould

One-year-old leaf mould is still relatively coarse and is best used as a mulch — spread 5–8 cm around perennials, shrubs, and fruit trees. Two-year-old leaf mould is finer and can be used as a soil conditioner, dug into beds to improve structure, or included in homemade potting mixes (up to 20–30%). It improves drainage in clay soils and moisture retention in sandy soils, and is particularly valued for seed starting where its fine, low-nutrient structure is ideal.