Determining Your Garden's Soil and Light

Clay or sand, sun or shade: those factors determine which plants will grow well and which may fail, so spend a little time getting to know your garden's conditions.

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©2011, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

©2008, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

©2011, Dorling Kindersley Limited

Testing Your Soil

There are two main types of soil particles: sand and clay. Sand particles are relatively large and water drains freely through the spaces between them, while clay particles are tiny and trap moisture in the minuscule gaps. This explains why sandy soils are dry and clay soils are moisture-retentive. Most soils are a mixture of both—tending to lean toward one or the other—but the ideal is loam, which contains almost equal measures of sand and clay. Loam retains enough water for plant roots to use, but also drains away excess moisture to prevent waterlogging. Test your soil type by digging some up and rolling it between your fingers.

Sandy Soil

When rolled between the fingers, sandy soil feels gritty, and when you try to mold it into a ball or sausage shape, it falls apart. It is also generally pale in color. The benefits of sandy soils are that they are light, well drained and easy to work. Mediterranean plants are happiest in sandy soil, because they never suffer from soggy roots. However, their poor water-holding capacity makes sandy soils prone to drought and lacking nutrients because nutrients are dissolved in water.

Clay Soil

Sticky and impossible to dig when wet and solid, cracked and impenetrable when dry, clay soils are hard to work. But in return, when looked after correctly, they have excellent water-retaining properties, and are rich in nutrients. Greedy rose bushes and fruit trees love to sink their roots into them.

Smooth and Sticky

Roll clay between your fingers and it feels smooth and dense, and retains its shape when molded into a ball. Soils very rich in clay will not crack even when rolled into a horseshoe shape. 

Top Tip: Testing Acidity

A simple pH test, available from the garden center, will tell you how acidic (lime-free) or alkaline (lime-rich) your soil is, and this will determine the range of plants you can grow. Add the supplied solution to a small sample of your soil in the tube provided. Wait until the solution changes color, then match the color to the chart.

Improving Your Soil

Whether you have a dry sandy soil or a sticky clay, the prescription is the same: lots and lots of organic matter, such as well-rotted manure, spent mushroom compost and garden compost. These bind together sandy soils and loosen dense clay soils, so ladle them on.

Sun or Shade?

Some plants like a hot spot, and enjoy basking in the sun all day long, while others prefer cool shade. Find out what your garden has to offer before you buy or start planting. Stand with your back to each of your boundaries and use a compass to figure out the direction that they face. If there's no canopy overhead, those facing south will be in the sun all day and hot, while those pointing north will be in shade most of the time and cooler. East-facing areas offer morning sun and evening shade, while the opposite applies to those facing west.

Check Your Plot

Patterns of sun and shade change throughout the day, and a garden that's in full sun at midday may have dark pools of shade by late afternoon, so spend some time watching your garden on a sunny day and make a note of the way shadows move around the plot. You can then plan what to plant where and identify areas for seating. Remember, too, that the patterns change depending on the season. A garden can look very different in low-light winter conditions, and areas that are in full sun for half the day in summer may not get any at this time of the year.