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Understanding Your Soil
Soil Types
Soils can be divided into three classifications: sand, loam and clay. Great variation occurs within the basic groups, but these categories suffice to describe where a given plant will grow.
Sandy soils, referred to as “light” soils, contain large soil particles that are loose and easy to work. They allow water to drain readily and typically are low in nutrients. Sandy soils tend to be more acidic than more fertile loams and clays. If your soil has a pH lower than 5, consider adding lime or wood ash to bring it closer to a desired pH of 6 or 7.
Clay soils, known as “heavy” soils, consist of very small, tightly packed soil particles, and tend to be hard to work. They are generally rich in nutrients, have a high water-holding capacity and can be very productive.
Loamy soils are “intermediate” between sand and clay. Composed of many different sized soil particles, they combine fertility, moisture-holding capacity and good drainage. Easier to work than clay and better consolidated than sand, loamy soils make an excellent medium for growing most plants.
Determining Your Soil Type
The Feel Test can help you determine your soil type. Take just enough moist soil to rub between the thumb and fingers. Rub it back and forth several times and feel it very carefully. A clay soil will be slick and smooth, with little or no grittiness. A predominantly sandy soil will be gritty and will not stick together well. A loamy soil will stick together easily, but not tenaciously like a clay. Loams will feel moderately gritty. As the soil dries between your fingers, rub it into a dust and feel it carefully. A loamy soil will have a component to it that feels like flour. This is silt, a soil particle size between sand and clay. Clays may also have a floury feeling to them, indicating silt content, but clay soil lacks the gritty sand component found in loams.
If you have difficulty determining your soil type by this method, dig into your soil when it is dry. A sandy soil will seldom exhibit clods. Any clods that do form will crumble easily. Loamy soils will have clods that can be sliced cleanly with a shovel. Clay soils tend to form hard, persistent clods. Rather than slicing through them, a shovel will get stuck or will shatter the clod into many hard, little blocks of soil.
Improving Your Soil
Add large quantities of organic matter to improve sand or clay soil. Avoid un-composted manure. It contains weed seeds and can “burn” plants. Compost and dead leaves are excellent. Do not use sawdust, wood chips, or similar materials, as these require a long time to break down and rob the soil of nitrogen. Organic matter holds more water and nutrients than any other soil constituent. It breaks up heavy soils, improving water intake and air exchange to plant roots, and firms light soil, enhancing nutrients and drought resistance. Organic matter modifies any soil, making it behave more like loam.
For an ecologically sound way to build soil organic matter, plant “green manure.” Buckwheat or winter wheat, for example, improves top soil by bringing nutrients from the lower soil and incorporating them via organic matter. The crop is plowed under while actively growing to incorporate the roots and leaves into the soil.
Tips for Working with Clay Soil
Augment clay soil with organic matter regularly to make it easier to work. Many prairie plants can grow in clay soils. With good initial care, these wildflowers and grasses will flourish even on difficult sites. Their roots will gradually work their way down into the clay, opening and improving it, just as these plants have done for thousands of years.
After seeding, apply 1-2 inches of weed-free straw mulch to maintain soil moisture and improve germination.
Be careful not to over-water! Clay soils drain slowly. Check the soil surface regularly for the first two months after seeding. When dry, water lightly in the morning.
Soil Moisture Affects Planting Decisions
Moist soil has a generous amount of water in the subsoil throughout the growing season. There may be standing water in the spring or fall.
Dry soil can include sand and/or gravel that drains readily and never has standing water, even after a heavy rain. Medium, or “mesic” soil includes well-drained loam and clay. These soils may have standing water for short periods after a hard rain.
See our Wildflower & Grass Selection Guide on our website at www.prairienursery.com to choose plants for your soil type and moisture conditions.
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