Many garden articles describe a fertile soil as “loamy,” but what does that mean? If you look at the diagram on the right, you’ll see that loam and clay loam are found in the middle, which means they have less than 50 percent clay and roughly equal percentages of sand and silt. This is a good thing (as Martha would say). To understand why, we have to understand the three mineral components of soil – known as sand, silt and clay. All three were once rock that has been broken down.
The soil-texture triangle is a graphic representation of the three mineral soil types.
Photo Credit: Courtesy of the University of Minnesota Cooperative Extension Service
Sand is the coarsest of the three and feels the roughest. Its individual particles are large and can’t fit closely together, so there are lots of large spaces between sand particles. These spaces, called macropores, allow water to enter quickly and drain away quickly, which is why sand is used for plants that need fast drainage, such as cacti.
The major problem with sand is fertilizer retention. Fertilizer can only be taken up by plant roots when it’s in liquid form, and when water containing fertilizer drains quickly, this doesn’t allow plants much time to “grab” the fertilizer. Ironically, sand is also the particle type most in need of fertilizer, since it consists of low-nutrition minerals like quartz.
Silt particles are intermediate in size and feel smooth like flour. It’s mechanically weathered rock. In other words, wind, rain and other elements once acted upon the rock to break it down into smaller pieces. Because water is often the medium that breaks up rocks, silt ends up in rivers and streams. (The term “silting up” means that large deposits of silt have collected to stop the flow of water, usually in a river or other body of water.)
Clay has very small particles that fit together very closely. The spaces between these particles are called micropores, which hold onto water for a long time. When it comes to fertility, clay is the opposite of sand; it’s richer to begin with and it also holds onto nutrients. Clay is sticky to the touch.
Most soils contain some sand, silt and clay. To determine what kind of soil you have in your garden, try this experiment:
Take a handful of soil and drizzle water onto it. Then make a fist. When you open your fist, are you looking at something that holds together completely (clay) or falls apart immediately (sand)? Most people have something in between – that’s a loamy soil.
Another method is to take a soil sample to your nearest County Extension Service office, where professionals there can also judge organic matter and nutrient content. Either way, understanding your soil is the first step to solving any garden problems, as well as a step in the right direction for growing healthy, beautiful plants.