The Dirt on Soil

Sometimes, it might feel like you need a degree in geology to understand the terminology used in gardening publications to describe soil. You may think to yourself, how complicated can soil be, isn’t it all just dirt? Well, there are a lot of different types of dirt and different components in each one. So here is the real “dirt” on soil.

Soil is made up of three basic mineral components: silt, sand and clay. Sand is coarse and rough to the touch (think sandpaper). Its individual particles are large and don’t fit closely together resulting in large spaces between the sand particles called macropores. These macropores allow water to enter and drain away quickly, which is why sand is used for plants that require excellent drainage, such as cacti. Macropores pose the problem of poor fertilizer retention. Fertilizer can only be utilized by plant roots when it’s in liquid form, and in sand it moves through too quickly to really do any good. Ironically, sand is most in need of fertilizer, since it consists of low-nutrition minerals like quartz.

Silt is just sand that has been further broken down by the erosive powers of nature: wind and water. We most often associate silt with the mineral rich soil on the banks and beds of rivers and streams. Silt particles are smooth and feel rather like baking flour to the touch.

Clay is extremely dense and has very small particles that fit very closely together. Just the opposite of macropores, the cramped spaces between these particles are called micropores. Micropores hold onto to water and nutrients. As any kindergartner can tell you, clay is sticky and thick to the touch.

Most soils contain some sand, silt and clay. So what really makes up the elusive and fertile “loamy” soil most gardeners strive for? What the pros consider “loamy” are soils that contain less than 50 percent clay and roughly equal percentages of sand and silt. So how do you know what type of soil of makes up your garden? Well there are a couple of ways.


The easiest way is to take a handful of your soil and drizzle water onto it. Make a fist and then open it, are you looking at something that holds together completely (clay) or falls apart immediately (sand)? This might not be the most accurate method but at least you’ll have an idea of what you’re working with. To really get down to the nitty gritty of what’s in your soil, take a soil sample to your nearest County or State Extension Service office, where professionals there can accurately judge organic matter and nutrient content. Either way, understanding your soil is the first step to making your garden grow.

If you do find that your soil is less than perfect for the garden you would like or are trying to grow, know that changing soil texture can be a difficult task. To improve gardening conditions, try adding organic matter or fertilizer first, rather than adding minerals to your soil. If this doesn’t work, consider adapting your garden by selecting plants that do well in the type of soil you have. No matter what type of soil is in your garden, always remember that even though soil is largely composed of non-organic minerals, it’s full of microscopic bacteria, fungi, actinomycetes and other soil organisms, so treat it well!

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