Understanding Your Soil
Getting to know your soil is an essential part of the garden design process. The type of soil you have in your garden determines how well it retains water and nutrients, how easy it is to dig and the type of plants that thrive in it.
The arrangement of particles in the soil is known as its ‘‘structure.” Sandy soils are made up of relatively large particles that leave big gaps, or pores, between them, while clay soils comprise tiny particles separated by minute spaces. It is not the size of the particles but the size of the spaces that determines how well or badly the soil retains water and nutrients. For example, sandy soils are free-draining because the large gaps between the particles allow water to flow through quickly. And because plant nutrients are dissolved in water, sandy soils can be less fertile.
The tiny pores between clay particles trap and hold water and nutrients. The downside is that clay soils become waterlogged very quickly, and the particles pack together in wet conditions when the soil is compressed, squeezing out the oxygen essential for plant growth. Walking on wet clay will further compact the soil.
Most garden soils are made up of not just one type of soil but a mixture. The best soil is moist but well-drained, fertile and easy to dig!
What type of soil do you have?
When rubbed between your fingers, sandy soil feels gritty and falls apart if you try to roll it into a ball. Coarse sand is free- draining, but very fine sand doesn’t drain well and can easily become compacted. Sandy soils are low in nutrients but easy to dig, which is why they are known as “light soils.”
This type of soil feels smooth and sticky, and can be rolled into a ball when wet. Clay is also porous and holds nutrients and water well, although plants cannot extract all of the moisture from clay, because an electrical charge on each of the particles holds it too tightly—rather like iron filings clinging to a magnet.
Acidity and alkalinity
Some plants, such as azaleas, only grow well on acidic soils, while others, such as acanthus, prefer alkaline conditions, so it is important to establish the pH (acidity or alkalinity) of your soil. Soil testing kits are available and easy to use. Take a few soil samples—the pH may differ throughout your yard.