Soil Organic Matter
Soil Health
Soil organic matter is the living and once-living material that gives garden soil resilience. It feeds soil organisms, improves structure and helps roots manage water and nutrients. Garden compost, well-rotted manure, leaf mould and green manure all contribute, making organic matter the foundation of long-term soil care in most UK gardens.
What it is
Organic matter includes decomposing leaves, roots, compost, manure and the organisms that process them. In mineral soil it helps particles form stable crumbs, improving both drainage and moisture retention. It provides a slow release of nutrients, though it is not a complete substitute for testing or balanced feeding. Sandy soils gain water-holding capacity; clay and silt soils become easier to work; loams retain their structure. Organic matter also supports worms, fungi and microbes that recycle nutrients. Its level declines where soil is left bare, intensively cultivated or repeatedly cropped without replenishment.
What to do
Add organic matter regularly as a 3 to 8 cm surface mulch, choosing garden compost, well-rotted manure or leaf mould according to what is available. Let worms incorporate it in a no-dig system, or mix it gently into the topsoil only where establishing a new bed. Sow green manure on vacant ground and return healthy crop residues to the compost heap. Do not use fresh manure around growing crops. Match additions to the soil: sandy ground benefits from frequent compost, while heavy soil needs mulch and protection from compaction. Use peat-free compost for containers and avoid disturbing carbon-rich peat soils unnecessarily.
Tips
Aim for steady annual improvement rather than one huge application. Keep a compost heap, leaf store or both so materials are available when beds are cleared. Organic matter improves nearly every soil, but it does not correct unsuitable pH by itself. Mulch after weeding, leaving a small gap around stems.
Soil Organic Matter: frequently asked questions
What is soil organic matter?
Organic matter includes decomposing leaves, roots, compost, manure and the organisms that process them.
How do I improve soil organic matter?
Add organic matter regularly as a 3 to 8 cm surface mulch, choosing garden compost, well-rotted manure or leaf mould according to what is available.
What are some tips for soil organic matter?
Aim for steady annual improvement rather than one huge application.
General guidance for UK gardens and allotments. Page updated 18 Sep 2026.