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Add a Mulch of Organic Matter (and Worms!) to Improve Clay Soils

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If you have heavy clay soil in your garden, you may find it hard to dig, slow to drain and quick to compact. But rather than seeing it as a problem, you can turn it into a productive, workable garden bed by improving its structure — by adding organic matter, mulch and encouraging worms and other soil life.

Why organic matter & mulch help
Clay soils are rich in nutrients but the fine particles make them heavy, slow to warm, and easily compacted. BBC Gardeners World Magazine+1
Adding well-rotted compost, leaf mould, farmyard manure or other organic matter helps bind the clay particles into more crumb‐like structure, improving drainage and aeration. Ideal Home+1
Mulching with organic matter helps retain moisture, moderate soil temperature and suppress weeds — and over time that mulch breaks down and adds deeper into the soil. GardenAdvice.co.uk+1

Encouraging worms & biology
Worms are nature’s soil engineers. They tunnel through heavy soil, bringing air and drainage, and their castings improve soil structure. By adding organic matter and keeping the surface covered with mulch, you encourage worm return and activity. (No-dig gardening practice emphasises this) Wikipedia
As the mulch breaks down, it becomes part of the soil, increasing organic matter percentage and making the clay easier to work. RHS

What you can do

  • In autumn or early spring, dig or loosen the top 15-20 cm of soil and incorporate several bucketfuls of well-rotted compost or leaf mould per square metre. Our site’s soil-preparation guide for clay suggests spent mushroom compost is one good material. GardenAdvice.co.uk
  • After incorporating, apply a surface mulch of organic matter (say 5-8 cm deep) over the area to keep feeding the soil biology.
  • Avoid walking heavily on the soil when wet — heavy clay compacts easily and undoing compaction takes time.
  • Over successive seasons you’ll find the soil becomes easier to dig, drains more freely, yet still holds moisture in dry spells.

Link for further reading
See our article: How to Deal With Heavy Clay Soil in the Garden which covers the long term approach including organic matter and drainage. GardenAdvice.co.uk