Category: Soil, Compost & Mulch Read time: 7 min read

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7 min read Easy Read Best read in Spring
Clay soilChalk soilSandy soilBuckinghamshireOxfordshireBerkshire

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Published

11 May 2026 · 7 min read

Last reviewed

19 July 2026

Reviewed by a senior CGM team member.

The short answer

Quick Answer

Use topsoil for levelling lawns, filling raised beds and creating new borders. Use compost for improving existing soil, mulching and feeding. For most garden jobs in the Chilterns, a mix of both is best. Cost: topsoil 30 to 60 pounds per tonne, compost 5 to 10 pounds per 100 litres.

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What Is Topsoil?

Topsoil is the upper layer of soil, typically the top 15 to 30cm. It contains mineral particles (sand, silt, clay) and some organic matter. Bagged topsoil is screened and graded. It is used for bulk: levelling lawns, filling raised beds, creating new borders. In the Chilterns, local topsoil is often chalky and alkaline, so imported topsoil may be needed for acid-loving plants.

What Is Compost?

Compost is decomposed organic matter. It is dark, crumbly and rich in nutrients. Garden compost is made from kitchen and garden waste. Bagged compost is commercially produced. It is used for improving soil structure, feeding plants and mulching.

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When to Use Topsoil

  • Levelling a lawn: spread topsoil over hollows and level
  • Filling raised beds: mix topsoil with compost for a balanced growing medium
  • Creating new borders: dig in topsoil to add depth on shallow chalky Chiltern soils
  • Building up soil level: raising the grade around a property
  • Repairing after building work: replacing soil removed during construction

When to Use Compost

  • Improving existing soil: dig in compost to add organic matter
  • Mulching: spread on the surface to suppress weeds and retain moisture
  • Feeding: compost releases nutrients slowly as it breaks down
  • Potting: mix with other ingredients for potting compost
  • Lawn top dressing: mix with sand for lawn top dressing

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When to Use Both

For most garden jobs, a mix of topsoil and compost is best:

  • Raised beds: 70% topsoil, 30% compost
  • New borders: dig in 5cm of compost, then top up with topsoil if needed
  • Lawn top dressing: 70% topsoil (sandy), 30% compost

Cost Comparison

  • Topsoil: 30 to 60 pounds per tonne (bulk), 3 to 5 pounds per 25kg bag
  • Compost: 5 to 10 pounds per 100 litres (bagged)
  • Farmyard manure: 6 to 12 pounds per 50 litres
  • Mushroom compost: 4 to 8 pounds per 50 litres

See our guide to compost types for detail on manure, mushroom compost and bark mulch.

What Not to Use

  • Subsoil: the layer beneath topsoil. Low in nutrients and organic matter.
  • Fresh manure: too strong, burns plants. Must be rotted for at least 6 months.
  • Peat: environmentally damaging. Use peat-free alternatives.

Get Help with Soil Improvement

If you need help choosing or sourcing soil improvers in Oxfordshire, Buckinghamshire, Berkshire or Bedfordshire, contact us on WhatsApp.

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Further Reading

Estate Note

In established gardens, soil structure takes decades to build. Avoid deep cultivation near mature trees and shrubs, as their fine feeder roots extend well beyond the canopy.

Useful next steps

Put this advice into practice

Use the relevant CGM tool or follow a related guide, then send us a few photos if you would like a tailored plan.

Open the plant planning toolOpen guide Low-maintenance plants for Chiltern gardensOpen guide Best plants for chalk soil in the ChilternsOpen guide
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Sources and citations

This article draws on the following sources. Specific claims are cited inline where relevant.

  1. CGM field records (2024-01. Site observations from gardens across Oxfordshire, Buckinghamshire, Berkshire and Bedfordshire.
  2. Royal Horticultural Society (2024). RHS Gardening Advice and Plant Finder. Available at rhs.org.uk.
  3. Met Office (2024). Regional climate averages, South East England. Available at metoffice.gov.uk.
  4. British Geological Survey (2024). Soil parent material data for the Chilterns and Thames Valley. Available at bgs.ac.uk.