Understanding Your Garden Soil

Loamy SoilIf you're really serious about growing a food garden that's sustainable and productive, it's vital that you have a basic understanding of your garden soil. In fact, the structure, texture and mineral makeup of the soil in your garden is just as important to your plants and vegetables as the amount of sun they get.

Garden vegetables have soil preferences, just like they have preferred amounts of sun exposure. So, try to grow a vegetable in an inappropriate soil type and you're bound to be left frustrated (and hungry). Don't know dirt about dirt? Here's a little soil primer to help you out.

The Dirt on Soil

A good way to think of your garden soil may be to think of it as having two key aspects: elements and composition. Soil elements are the "parts" of your soil: they're the bits and pieces of minerals (the actual particles) that make the earth (the sand, silt, clay, and organic matter). Soil composition encompasses the characteristics of your soil: it's how those parts affect different traits of your dirt (like texture, structure and fertility). Because soil elements are heavily influenced by geography, this means that where you live can (and will) have a huge impact on the natural characteristics of your soil.

What Elements Make Up Garden Soil?

Most garden soil is basically made of four main elements (not including soil amendments like manure and fertilizers). It's the ratio of these elements in your dirt that determines your soil composition.

  1. Sand. Yep, just like sand at the beach, these are the tiny, loose grains of rock that water just seeps through. Sand is an essential element of soil because its irregular surfaces and particle sizes create air pockets that allow water drainage.
     
  2. Good garden soilSilt. Silt is that sand-like sedimentary material found near streams, rivers and lakes. Silt particles are are smaller than sand but larger than clay.
     
  3. Clay. Clay is the soil element that gardeners fear most because it's made of extremely small particles that compress and lock out air and water. When clay soil (also called heavy soil) is too wet, it's gummy, thick and hard to work with. When it's too dry, it bakes and basically becomes brick. (Have a garden nemesis? Slowly and surreptitiously replace all of her soil with clay, then sit back and watch her slow and inevitable descent into foul-mouthed madness.)
     
  4. Organic matter. Organic matter (which includes humus and compost) is plant or animal residue in various stages of decay. Humus refers to well-decomposed plant matter, whereas compost can really refer to organic matter at any stage of decay. In healthy soils, microorganisms associated with this organic matter help to clump together mineral and organic particles, which promotes internal drainage and air circulation (which is good for root development and growth).

Garden Soil Composition (Soil Structure and Texture)

Not sure what elements your garden soil is made of? Examining your soil composition is the key.

  • Clay soilClay soils. Think you might have clay soil? Wet clay soil feels greasy when rubbed between your fingers and will readily clump into a ball when wet. The nice thing about clay is that it slows down drainage (so you don't have to water or fertilize as often). The flip side of that benefit, however, is that because it slows drainage, it can also promote root rot. Plus, heavy soil is just a beast to work with: it's gummy when wet and rock-hard when dry.
     
  • Sandy soilSandy soils. Also known as light soil, sandy soil is basically the opposite of clay soil: It's light, drains easily, and makes it easy for plant roots to establish themselves. To see if you have sandy (or silty soil), try pressing your garden soil (when damp) into a ball. If it feels gritty, falls apart, and will not hold shape at all, it's sandy. The nice thing about light soil is that because it drains water so well, plants are less likely to suffer from root root. Unfortunately, this also means more frequent watering, which leaches away nutrients.
     
  • Silty soils. Less common than but similar to sandy soil is silty soil. Detecting silty soil can be hard because 1) it looks a lot like sand and b) it's a bit subjective: it's not quite as gritty as sandy soil but it also tends to dry hard and resist water penetration like clay. If, when rubbed between your fingers, your garden soil feels silky (as opposed to gritty), you probably have silty soil.
     
  • Loamy SoilLoamy soils. Often just called loam, loamy soil is the soil you dream about. It's that blissful mix of sand, silt, clay and organic matter that's fertile, retains moisture and nutrients, and is loose enough to allow roots to establish themselves. While not all vegetables grow best in loamy soil, many do, so it's usually considered the best to have.To see if you have loamy soil, take a handful of garden soil and press it into a ball. If it crumbles slightly but still retains some of its shape, it's loamy.

Looking for other in-depth information on growing a healthy, productive garden (like preferred soil pH, planting depths and germination rates for different vegetables)? Check out the Gardening Guides page for a full list of gardening resources.

Images thanks to Axonite, asifthebes, ajmac, mzacha and rams_on.