Gardening glossary
Leaf mould
Leaf mould is autumn turned into soil. Unlike compost, which is dominated by bacteria and runs hot, leaf mould is a slow, cool, fungal decomposition of fallen tree leaves. The result after one to three years is a fine, dark, crumbly material with a mild earthy smell and the texture of damp tea leaves.
What makes leaf mould different from compost:
- **Lower in nutrients.** Leaf mould is not a fertiliser. NPK values typically run 0.5-0.2-0.3 — a fraction of compost. Its value is in structure and water-holding capacity. - **Higher in fungal biomass.** Garden compost is bacterially dominant; leaf mould is fungally dominant. This matters because most perennials, trees, and shrubs prefer a fungally-dominant soil. - **Excellent moisture retention.** Well-rotted leaf mould holds 200–300% of its dry weight in water, making it brilliant for woodland plants, hostas, ferns, and as a seed-starting medium.
How to make it. Rake fallen leaves in autumn, pile them in a wire mesh cage or stuff them (slightly damp) into black bin bags with a few air holes punched in the sides. Leave alone for one year for rough leaf mould (good as a mulch) or two to three years for fine, sieveable leaf mould (good in potting mixes). Beech, oak, hornbeam, and birch leaves break down fastest; sycamore, plane, and conifer needles are slower.
Uses in the garden:
- **Mulch** around shrubs, roses, and perennials at 5 cm thick. - **Soil conditioner** mixed at 25% into vegetable beds. - **Seed-starting medium** — sieved leaf mould mixed 1:1 with garden soil or peat-free compost makes a near-perfect medium for fine seed. - **Substitute for peat** in containers — well-rotted leaf mould has similar water-holding properties without the carbon-release cost of peat extraction.
A free, almost-zero-effort amendment that improves any soil it touches. The only cost is patience.