What's Your Soil Type

Soil is more than just something to hold your plants upright and in place.

Sometimes we think of it that way, though. Fact is, it’s that and more. It provides the elements that plants need to grow.

Unless you’re growing hydroponically (artificially in soil-less, nutrient-rich solutions), you need to know what type of soil you have, if you’re going to garden successfully. It’s true even if you’re growing in containers.

As noted in a previous article, soil consists of solids, liquids and gases. Let’s consider the solids. They include:

• Minerals – Inorganic solids with definite chemical compositions in crystal forms formed by geologic processes. Examples include magnesium, sodium, iron, copper, and zinc.
• Organic matter – These are left-overs of dead plants and animals. Examples include shells, bones, hair, feathers, leaves, grass, wood, and such cell structures in various stages of decomposition.
• All of those help to nourish and support your plants.

These are the basic soil types.

I did a web search for soil types to see what answers would turn up. Some returned as few as four types. One search returned twelve! While it might not be as precise, I prefer the fewer.

With the exception of one type, the difference between the other three amounts to the size of the soil particles. Those would be:

• Sand – This includes the largest of the particles. Each one is usually visible to the naked eye. Liquids and gases can easily flow between them, maybe too fast. Dry particles typically do not cohere.
• Silt – Silt particles are somewhere between the size of sand and clay. They are produced by the action of water, becoming sediment. When wet, silt coheres, but remains somewhat crumbly.
• Clay – Clay includes the finest of all soil particles. Many are flat in shape. When wet, clay is plastic. When dry it becomes brick-hard.
• Loam – It’s a combination of the other three soil types. Here the combinations are many. They are named according to the particle sizes, their predominance, and, often, the location where they are found.

A good example is Tifton soil – a soil of Georgia. A Wikipedia article describes it like this:

A typical Tifton soil profile consists of an 11 inches (280 mm) topsoil of dark grayish brown loamy sand. The subsoil extends to about 65 inches, strong brown fine sandy loam to 22 inches; yellowish brown sandy clay loam to 40 inches; yellowish brown mottled, sandy clay loam to 60 inches, and strong brown, mottled sandy clay to 65 inches. Two distinctive features of the Tifton soil profile are the presence of more than 5 percent ironstone nodules in the upper part of the soil and more than 5 percent plinthite in the lower part of the soil.

Tifton soils are on nearly level to gently sloping uplands of the Southern Coastal Plain. They formed in loamy sediments of marine origin. Tifton soils are among the most agriculturally important soils in the state.

Learn more by observation or the official soil maps.

It’s important to know your soil type because it informs you about the possible success or failure of your plant choices and landscaping plans. You can learn your soil type by simple observation, but if you want to be more sophisticated about it, go to the interactive USDA Web Soil Survey web site. According to the site, “NRCS has soil maps and data available online for more than 95 percent of the nation’s counties and anticipates having 100 percent in the near future.” Thanks to your tax dollars at work, you can probably drill down to your own location, and get the official nitty-gritty about the dirt under your feet.

What about organic matter?

Well, that’s called humus. Humus is the organic component of soil. (It is not to be confused with hummus, which is organic matter of an edible sort.) Humus is made up of decomposed plants and animals. It helps with water retention in the soil, and also provides many nutrients to your plants in readily available form.

What you should do about your soil.

If you have sandy loam, loamy clay, or any of the other combinations, there’s not a lot you can do about it. If you have perfect garden soil, consider yourself lucky. But, what if  your soil is much less than ideal? Short of a major excavation project, you’ll always have it under your feet. Even then, you can only excavate so deep. I think you ought to just learn to live with it, but living with it still means you can improve it to some degree with the addition of soil amendments.

The helpful folks at your local Cooperative Extension Office can advise you about that. They should know what measures have been successful, and what have not.

For example, Iowa State Hort News states, “Advertisements for gypsum sometimes claim that gypsum will help loosen heavy, clay soils and improve soil drainage. However, the addition of gypsum to Iowa soils is of little benefit.”

Experts at Washington State University concur. “With the exception of arid and coastal regions (where soil salts are high) and the southeastern United States (where heavy clay soils are common), gypsum amendment is just not necessary in non-agricultural areas.”

Cooperative Extension agents in other states might advise differently.

Adding organic matter (humus) to your soil is always a good idea, and composting is one of the best ways to achieve it. My article, The Not-So-Magical Experience of Composting, gives a basic idea of the process.

Soil improvement is an ongoing project.

Keep in mind that soil improvement – especially adding organic humus – is an ongoing process. About 30 years ago, when I was intent on improving the organic matter of my Tifton loamy-sand, a farmer friend told me I could add it ‘til the cows came home, but it wouldn’t do any good. The reason being that the heat and humidity here breaks down organic matter so quickly it won’t build up on the soil. He was right. After three decades of growing and mowing clover and rye grass, there’s less than 1 inch of organic matter on top of my acres of loamy sand. I’m not saying it hasn’t done some good. I’m simply saying you have to keep on keeping on.

Building a thick layer of humus in a few flower beds or vegetable garden should be easier because you have less area to work. This would be especially true in raised bed gardening. Even so, dig down a foot or so; you’ll probably find your native soil just as it was before.

My last word on the subject…maybe.

Choose your plants to match your soil type, not the other way around. You have arid, sandy soil? Plant something that thrives in it – cactus, perhaps. (By the way, check the GoGardenNow – The Gardening Blog articles on xeriscaping.) You have heavy, clay soil? Select plants that love it. Same goes for any other soil type.

The bottom line is that knowing and understanding your soil type will help you make better decisions about how to manage it, and to select plants that will improve your chances of gardening success.