Soil testing

More than any other factor, the quality of your soil will determine how successful you are in the garden. Understanding your soil’s texture, structure, drainage properties, and pH will help you make the most of your garden. Use these simple tests to gain an insight into the type of soil you’re working with.

Why test soil?

Soil is a living thing, with millions of micro-organisms and small creatures in a single handful. It is an unbelievably complex part of the natural system.

Unfortunately, gardening upsets the delicate balance between the various elements – a disturbing but inescapable fact. This means that your soil’s condition will either be better or worse at this time next year. Which one depends on what you do before then.

Before drawing up an improvement plan it’s important to know your soil’s texture, structure, drainage properties, and pH. These will determine what needs to be done.

Soil texture

Soil texture refers to the proportions of different-sized mineral particles which are present in the soil. When coarse (sand) particles predominate the texture is heavy. When minute (clay) particles are plentiful the soil is described as light. Use the steps below to test your soil’s texture.

How to test soil texture

• Using a garden spade dig a five-inch (13 cm) hole in four locations throughout your garden. Extract a vertical segment of soil from the side of each hole.
• Put all segments into a container and mix well. You should have at least 3 cups of mixed soil. Remove any sticks, pebbles and plant parts from the container of soil.
• Place 1 cup of mixed soil into a jar. Fill the jar nearly to the top with water. Add 1 teaspoon of dishwashing detergent, cover, then shake the jar well. Position the jar in a location where it won’t be disturbed for 48 hours.
• After 1 hour you will notice a distinct layer has settled to the bottom. This is the sand layer. Using a permanent marker, draw a line on the jar to mark the top of this layer.
• After 3 hours you should notice a second layer. This is the silt layer. Mark the top of this layer with a marker.
• After 48 hours, or when the water is clear, mark the top of the next, clay layer.
• Measure the height of each layer to establish the relative proportions of sand, silt, and clay. Classify your results – 55% clay = clay soil; 85% sand = sandy soil; 85% silt = silt soil.

Soil structure

Soil structure refers to the way mineral particles are joined together in the soil. They may be almost unconnected as in very light soil with little organic matter or they may be grouped in clods, plates or crumbs in a heavy soil. Use the hand test below to test your soil’s structure.

How to test soil structure

• Pick up a handful of soil – dig down a couple of inches (5 cm) if a mulch has been applied. If the soil is dry, moisten just enough to hold the soil together.
• Knead in the palm of your hand to break down lumps. Squeeze the sample.
• Determine your soil structure by considering the following:
• Heavy (clay) soil – The soil forms a strong ball – when pressed it changes shape but does not fall apart. The ball feels smooth and sticky when wet.
• Light (sandy) soil – The soil ball crumbles and sifts through your fingers. A small sample feels or sounds gritty when rubbed between finger and thumb. Does not stain the skin.
• Medium (loamy) soil – The soil forms a distinct ball – when pressed it loses its shape and crumbles. It may feel slightly gritty – usually stains the skin.
• Chalky soil – The soil forms a distinct ball – when pressed it loses its shape and crumbles. The color is black with white flecks.

Soil pH

Soil pH is a measure of the alkalinity or acidity of a soil and has a significant impact on plant growth and nutrient availability. Crops grown in extremely high or low pH soils produce lower yields and tend to suffer from nutrient deficiencies. Use the steps below to test your soil’s pH.

How to test soil pH

• Purchase a simple kit to discover the pH value of your soil. Your local gardening store should stock a range of testing kits.
• Following the instructions, place a teaspoon of soil on the test card, then add drops of the indicator liquid.
• Stir the soil sample and add more drops of the indicator liquid to make a thick paste.
• Sprinkle the testing kit powder onto the paste, then wait for 2 minutes until it changes color.
• Match the color of the soil sample with the nearest pH value on the color card. Purple is alkaline; yellow is acid; and green is neutral.

Soil drainage

How quickly water moves through your soil will impact plant growth. Poor drainage prevents plant roots from obtaining oxygen. Oxygen-starved soil not only suffocates plants, but earthworms, and other beneficial soil organisms. Use the steps below to test your soil’s drainage properties.

How to test soil drainage

• Dig four holes, each about a foot deep and a foot across, spaced several feet apart.
• Fill each hole to the top with tap water. Note the time and depth of the water in each hole.
• Return after an hour and note the time and depth for each hole.
• Repeat after two and three hours then calculate the average inches lost per hour.
• Water in well-drained soil should drain about an inch per hour. If your water disappeared much faster, your soil is poorly drained. If it took much longer, your soil is poorly drained.