Getting and keeping good soil is the most important ingredient in a successful garden and will do more to make plants grow and thrive than any other gardening technique. Whether soil is defined as ‘good’ or not depends mainly on its composition, texture and the nutrients it contains.
Soil type is determined by particle size and how soil particles interact. This is determined by the proportion of sand, organic matter and clay particles that make up the soil’s composition. The ideal garden soil is crumbly, easy to dig and is roughly equal parts sand, silt and clay (the basic mineral components of soil) and organic matter.
- Clay soil has particles with tiny spaces between them causing the particles to stick together creating a heavy and compacted consistency. Clay packs down so there is poor aeration and drainage.
- Sandy soils have large particles with large spaces between the particles, thus allowing air and water to move easily.
- Silt has some of the qualities of both sand and clay.
- Loam soils are a mixture of sand, organic matter and clay in roughly equal proportions and are well drained. Loam soils generally contain more nutrients and humus than clay or sandy soils.
The texture or tilth of soil relates to how easy it is to dig, how easily seedlings can emerge and whether the plants’ roots can penetrate deeply into the soil. A soil that has a crumbly texture, drains well, yet has the capacity to hold water is said to have good tilth. Most plants prefer a ‘loamy’ soil that is rich in organic material and that doesn’t drain too quickly. There are exceptions of course. Cacti, for example, prefer a quickly draining, sandy soil
Know Your Soil
Knowing what kind of soil you are dealing with is the first step to improving it. Finding out is easy. I call it the ‘squeeze test’. Here’s how:
- Add a little water to a small amount of dry soil and try to squeeze it into a ball.
- Knead the soil between your fingers to form a flat ribbon.
- To determine the texture of your soil, measure the ribbon.
If you can’t create a ribbon and the soil falls apart you have sandy soil. If the ribbon measures less than 2.5 cm (1 inch) long before breaking up, you have loam. If the ribbon sticks together and measures more than two inches long before breaking up, then you have clay.
Improving on Mother Nature
Most of us are not blessed with perfect soil for our gardens. Amending any type of soil with organic matter helps to improve its texture, aeration and drainage and adds nutrients too. Organic matter such as kitchen compost, peat moss, leaves (gathered in the fall), needles from conifers and sawdust are examples. Manure can be used as an amendment, but it must be well rotted to avoid burning the plants’ roots. Be aware that manure may contain weed seeds. Adding coarse builder’s sand to heavy clay soils improves drainage and allows more oxygen to reach the plants’ roots.
For new gardens spread soil amendments evenly over the area and work it into the soil to a depth of about 25 cm (10 inches). For existing beds, the soil can be improved every time you plant.
Avoid working the soil when it is wet. Wet soil compacts into hard clods. To check the soil for dampness, squeeze a handful of soil into a ball, and then push your thumb into the ball. If it crumbles, go ahead and work it, if not wait until it dries out more.
Building Soil Fertility
Homemade garden compost and composted manures are good sources of plant foods that won’t burn roots and can be used throughout the season. Leaves, shredded or whole, incorporated into garden soil or used as surface mulch, encourages worms to establish colonies and distribute their nutrient-rich castings throughout the soil.
Since organic matter is not a balanced fertilizer, many gardeners like to apply a commercial fertilizer to encourage plant growth. Be sure to carefully follow the directions on the label.