Guide to Garden Soil

Determine the type and quality of your garden soil to ensure healthy plant growth.

Dig Test Holes to Evaluate Quality of Soil

Dig Test Holes to Evaluate Quality of Soil

Dig test holes to assess the quality of garden soil. Also look out for other potential soil problems.

©2011, Dorling Kindersley Limited

2011, Dorling Kindersley Limited

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Before you decide what to plant in your garden, take a look at the soil. The acidity or alkalinity of the soil and its composition determine what will grow, and an understanding of its properties helps you keep plants in good health.

Types of Soil

Soil comprises two elements: a mineral portion (tiny particles of weathered rock, larger gravel, and stones) and an organic portion (plant and animal remains, and living organisms). The most important part of the soil is found in the top 12 inches (30 cm). Below this lies less fertile subsoil. Soil particle size, the amount of organic matter, and available water determine soil characteristics. The smallest soil particles will form clay, those a little larger create silt, and even bigger particles form sandy soil. Soil with a mix of different particle sizes is known as loam. 

The descriptions below will help determine your soil type:

  • Chalk soil: Soil that is pale and contains chunks of white limestone (usually the underlying rock), and often flint, is chalk soil. It is free-draining and fertile, often rather thin, and almost always alkaline.
  • Peat soil: Distinctively dark, peat soil is rich in organic matter that helps it retain soil moisture. Peat forms where wet, acidic conditions stop plant and animal remains from decomposing fully. Peat soil is usually acidic.
  • Clay soil: Composed of more than 25 percent moisture-retaining clay particles, clay is heavy to dig and may be waterlogged in winter (it dries out in summer). Organic matter is easily trapped, resulting in good fertility.
  • Silty soil: With particles not as fine as those of clay soil, silt is also fairly moisture-retentive and fertile. Silty soil tends to be dark in color, which is the result of the accumulated organic matter that it often contains.
  • Sandy soil: Sandy soil is easy to spot, being light and free-draining. It is composed of relatively large individual soil particles that allow water to drain quickly.

Testing the Soil’s Acidity or Alkalinity

Use a soil-testing kit to assess the acidity or alkalinity (pH) of your soil—the results will indicate what plants will grow well. Carry out several tests across the garden, using soil from just below the surface. Soil pH is measured on a scale of 1–14. Above neutral (7) is alkaline, below is acidic; pH 6.5 is usually considered the optimum.

Following the kit’s instructions, add garden soil and water to the test tube provided and shake the contents well. Compare results from around the garden with the chart provided: a red/yellow color shows an acidic soil; dark green an alkaline one.

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