Tidal marsh soil profile in the cutbank of a creek, the result of accretion and erosion, layers of clay with small fragments of shells

Georgia real estate sales have been doing very well these days so my Realtor friends say. With the influx of new homeowners, it’s a good time for a refresher course on the soil beneath our feet, for what lies below where one is standing is key to a successful landscape. Soil varies depending on location. The state of Georgia can be divided into three geographic regions: mountains, piedmont and coastal plain. There are six major soil provinces: Limestone Valley and Blue Ridge (mountains), Southern Piedmont (piedmont), and Sand Hills, Southern Coastal Plain and Atlantic Coast Flatwoods (coastal plain). As one goes from north to south, the changes in soil types is very evident – red clay to sand.

Basically, soil is clay, silt or sand. In various percent combinations of one another, they can make sandy clay and silty clay. When all three are combined, the soil is known as loam (mixture of sand, silt and clay). Based on the percent of sand, silt and clay, the loam soil can be silt loam, sandy loam, clay loam, sandy clay loam, silty clay loam and loamy sand. For instance, a soil made up of 50% sand, 30% clay and 20% silt is a sandy clay loam.

Clay soil is defined as having 25% or more clay particles. Clay particles are thin, flat and covered with tiny plates. They are the finest of all the soil particles. The spaces between clay particles allow clay to hold a high amount of water. In addition, the clay surface has the ability to hold nutrients due to its electrostatic surface charge (–) that attracts the positively charged nutrients (+) known as cations such as potassium, magnesium and calcium. This ability to attract, hold and exchange nutrients is called the cation exchange capacity or CEC and is a measurement of soil fertility. Clay expands with water and contracts as it dries. It is very sticky when wet. A soil high in clay makes planting a difficult chore. Silt is a sediment material that is very fine, with a particle size that falls between clay and sand. It can be easily formed into various shapes and when very wet, it will form fine, runny puddles of mud. Silt is easily carried by flood waters and deposited on valley floors. Silt retains water and nutrients. However, it can become easily compacted and poorly drained. When dried, it is easily eroded by wind and water. Sand consists of rock particles and hard minerals. Sand has the largest size of soil particles. Each particle can be seen by the naked eye. Depending on the size, you may actually be able to feel the grainy texture when you rub the soil between your fingers. The particles also make the soil crumbly. The benefit to the large size of sand particles is an increase in soil drainage and aeration. The disadvantage to sandy soil is that it dries quickly, is often low in nutrients and often has a low pH. Water and fertilizer are easily leached out before plant roots can utilize them. Loam exists as a combination of the three soil types, and benefits from having all the qualities of each soil type in one soil: water retention, fertility, air circulation and drainage.

Soil pH is a quality of soil that measures the degree of soil acidity or alkalinity. It alters the physical, chemical and biological properties of the soil thereby affecting plant nutrient availability and ultimately, plant growth. The range of pH is 0-14 with pH below 7 being acidic, pH of 7 being considered neutral and pH above 7 being basic. Plants grow best in a soil pH of 6.7 in which the most nutrients are available to the plant. One of my thickest academic books was about soil chemistry. I could delve deeper into this topic, but I might lose myself as a writer and maybe some of you readers. Suffice it to say that there is a whole lot of complex things going on underground than one may think.

Soil organic matter is also important. Organic matter is composed of the living (microbial mass that decomposes organic matter), the dying (decomposing plant and animal matter) and the dead (final decomposition, humus). The first two components contribute to soil fertility because the breakdown results in the release of nutrients needed by plants. The third component known as humus doesn’t add to the fertility but is the stable organic component that contributes to soil structure and the cation exchange capacity. Therefore, the characteristics of a good soil include enough organic matter to enhance the moisture holding capacity while remaining well-drained, a high CEC or nutrient holding capacity and a pH around 6.7. With experience one can actually feel, smell and even taste a good soil. Good soil is friable with just the right amounts of sand, silt, clay, loam and organic matter. When one takes a handful of it and makes a tight fist, the soil remains in a ball in the palm of the hand. When tapped lightly, the ball easily crumbles, a great quality for root growth. Too much clay results in a sticky, solid ball. Too much sand results in no formation of a ball and is easily blown away. Good soil has a clean smell. A lightly basic soil tastes somewhat sweet while an acid soil will be tart. Yes, I am serious!

So, what is the soil type below your feet? To find out, start with a soil sample which reveals the health and fertility, the pH and the CEC of the soil. All the information on how to do this can be found on the web or by stopping at the local county extension office. Also, a simple test can be done for drainage. Simply dig a hole about 12 inches deep and equally wide. Fill it with water. Let it drain, refill it 12 hours late and record the time it takes to drain the second time. If the soil is well drained, all the water should be gone in two to three hours. One can also wait for a significant rainfall to see where the poorly drained and well drained areas are located. Improving the soil takes time but it’s well worth the effort because successful gardening starts from the ground up.