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| Photo Credit: Courtesy of the University of Minnesota Cooperative Extension Service |
| The soil-texture triangle is a graphic representation of the three mineral soil types. |
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.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.)
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