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Understanding Your Soil              Bookmark and Share

Of course you want your plants to do well, so you stop and read the tag (or look up in a book) exactly what conditions the plant needs. Plant in rich, well-drained soil… Prefers soil with high organic content… Amend the soil with humus. That may be what the instructions say, but as most gardeners know, you rarely find soil that naturally meets these criteria. What exactly do they mean by all those terms? Most of us have to work with the soil we have, amending it to make it as close to the ideal soil as possible. Understanding what soil really is and how it all fits together makes that an easier job.

Soil is made up of two components. Soil is composed of minerals, in the form of sand, clay and silt and organic components such as plant material, manure, decomposing animal/insect parts, water, air and living organisms. The balance between the different parts is what makes your soil a joy to work with or a challenge.

Texture is determined by the relative amounts of sand, silt and clay your soil has. A soil’s texture greatly influences drainage and ability to hold nutrients.

Soil particles are classified according to size. Sand has the largest pieces and they are usually very irregular in shape, so they don’t pack. Clay has the smallest pieces and can pack so tightly water can’t easily get through. The in-between size pieces are called silt. Silt particles are irregular like sand, but they are usually coated with clay, making it act like both. At home you can take a handful of soil that is fairly dry and workable and squeeze it into a lump. Soils high in clay will form a clod that won’t easily crumble like soils with lots of sand and silt. Get some wet and rub it between your fingers. Clay feels slippery when wet and sand feels coarse and rough. Without sending a sample to be analyzed, you can do a test at home, that will tell you the approximate proportions of clay, silt, sand and organic matter. Take a representative sample of your soil and let it dry out a few days. Break up the soil and take out any rocks or sticks. Fill a clear jar 1/3 with soil and mark the level on the jar. Fill it with water and a few drops of dish soap and shake for a minute to get everything stirred up and floating. Set it aside. The soil will immediately begin to settle. After one minute, the sand will have settled out – mark that level on the jar with a grease pencil or marker. Make another mark after two hours to indicate how much silt settled out. After a day, most of the clay will have made up the next level. You may have a small layer of other stuff on top of the clay (or bits and pieces floating around). That is your organic matter (compost, leaves, etc.). Organic matter is essential to a healthy soil. The organic part of your soil is alive, always changing, building and breaking down. All the activity that goes on, in the organic part of the soil, provides the food for the billions of microorganisms that live there. In turn, the microorganisms convert nutrients into forms that plants can use.

How the different parts of the soil are grouped together determine its structure. Ideally, you would like it all to be soft and crumbly, staying loose and well drained. Since it’s hard for anything to stick to sand, sandy soils tend to be too loose and let too much water through. Clay soils can be worse, because they pack so tightly water can’t drain through and the air is squeezed out. Most of a soil’s structure is determined by nature, but we can have positive (through good gardening practices) or negative(compaction and erosion) effects with our management.

Everyone has probably noticed that the soil seems to vary as you dig. A cross section of the soil 2-3 feet deep will reveal its profile, showing different layers, colors and textures. Your topsoil is the richest, with the most organic matter and life, and easy to amend. Below your topsoil is the subsoil, which has almost no organic matter and is extremely hard to amend. Loam is a general term applied to soil that has relatively equal parts of sand, clay and silt. You might even see terms such as sandy loam or clay loam, indicating it has a little more of that component. Humus refers to organic material that comes from animals and plants (such as peat, manure and compost). Humus breaks down readily in the soil, releasing its nutrients. Soils with lots of humus are called rich soils… soils with very little humus are called lean.

When you are working with your soil, take a sample and have it tested for the nutritional levels and pH in your soil. We’d be glad to provide you with the form and sample bag to send to the University of Minnesota Soil Labs. Even though it costs a few dollars, having this done every year or two can save you lots of frustration and guess work. There are also a few home tests on the market that will give you a ball-park reading. Using distilled water with home tests will give you more accurate results.

If you are getting ready to plant an area, it is the best opportunity you will have to add to the soil without disturbing the plants. Organic matter breaks down over time and adding more each time you plant will pay off in the long run, no matter
how good your soil is to start.

Recommended Products
Baled Peat Moss
Bagged Soil Amendments
Pelleted Lime and Gypsum
Additional Bachman’s Information
Soil pH
Soil Tests
Working With Clay Soil

©Bachman’s 2010

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