We too easily fall into the habit of thinking of soil as a mere container that provides our plants with physical support. Beyond this, healthy soil is a vibrant community made up of a multitude of organisms ranging in size from earthworms and ground beetles to microscopic bacteria and fungi.
Tiny particles of rocks and minerals make up about 90 percent of most soils. The sizes of these particles determine the physical characteristics of the soil.
Sand (large particles) drains quickly and may be low in nutrients.
Silt (medium particles) has a good balance between moisture-holding capacity and air spaces.
Clay (small particles) tends to drain slowly and may be too wet and lacking in air spaces for successful plant growth.
* Living and dead organisms, roots, and plant wastes make up most of the remaining 10 percent of soil. This is the part that you can manage and adjust for your garden’s benefit. A single cup of healthy garden soil may contain more than 6 billion microorganisms, most of which work for the good of your garden.
Get to Know Your Soil
Feel the texture
* Knowing your soil’s texture will help you to decide how to manage it effectively. Clay soil, for example, holds moisture and can keep roots too wet for healthy growth. You can amend clay soil with coarse organic matter, such as bark chips, while avoiding mulches that also hold moisture.
Take a handful of moist soil and squeeze it in your fist. What happens when you open your hand? If the soil falls apart, chances are that it has a significant percentage of sand. If it remains in a ball, attempt to squeeze it into a ribbon shape between your thumb and forefinger. If you can’t make a ribbon from the ball, your soil is sandy loam; if you can form a ribbon, see how long you can make it. The longer the ribbon, the more clay is in the soil.
Add some water to the soil in your hand and make a muddy paste. Use the forefinger of your other hand to rub the mud. Does it feel gritty? (Sand.) Does it feel smooth? (Silt or silty clay.) Or both gritty and smooth? (Loam, clay loam, or clay.)
* The classic “earthy” aroma of healthy soil comes from humus, the product of decomposing organic material. A handful of moist soil should smell earthy. Sour odors may indicate poor drainage; chemical smells may be the result of contaminants or residues from fertilizers or pesticides.
Count the earthworms
* Earthworms contribute to soil health by feeding on decomposing organic matter and excreting it as castings, which improve the availability of nutrients in the soil and promote the formation of soil aggregates. Worm tunnels in the soil create passages for air and water, as well as for growing roots. To take a snapshot of your garden’s earthworm quotient, mark out a 1-foot-square area and remove the soil to a depth of about 6 inches. Put everything from the hole into a bucket. Gently sort through the contents of the bucket and count the earthworms. The presence of at least 10 worms indicates good, healthy soil. To get accurate results, do this test in the early summer when the soil is still moist and at least 55[degrees]F.
Why pH Matters
Soil pH determines what nutrients in the soil are available for plants to use. Iron, for example, is most soluble in acidic soil. Iron may be plentiful in soil with a pH of 7, but some plants will display symptoms of iron deficiency because the iron is in an insoluble form that’s unavailable for their roots to absorb.
Similarly, plants can miss out on other nutrients that become insoluble when the soil pH is low.
In either situation, your plants’ symptoms (or the results of a soil test) may reveal what nutrients are lacking. Consult your local Cooperative Extension office or a knowledgeable garden center to positively identify deficiency symptoms; then apply fertilizers to remedy the imbalance.
Correcting the problem in this way is a short-term fix, however. For the long term, you may want to modify the pH of the soil to better suit the plants that you wish to grow at a particular site.
To Fix It, Mix It
Complement your soil’s native properties with amendments that enhance its overall qualities. Remember: Soil amendments take time to have the desired effects and are best applied in the fall to allow for gradual incorporation over the winter months. It’s easier, too, to amend garden beds when they’re empty.
Bark chips: Add these to any soil that needs a boost of organic matter; they also improve drainage in heavy soil. Bark chips break down slowly, providing a long-term source of organic material for microorganisms, but they may need to be balanced with an additional nitrogen source, such as alfalfa meal, so that they do not rob nitrogen from your plants.
Compost: The perfect conditioner for practically any soil type, compost acts as a mild fertilizer by introducing beneficial microorganisms that enhance overall nutrient availability. It also improves drainage in clay soil and increases the moisture-holding capacity of sandy soil. If you do just one thing to improve your soil, choose compost.
Gypsum: A powdery amendment that supplies calcium and sulfur, gypsum loosens and helps to improve soil structure in clay soil that has a neutral to alkaline (above 7.0) pH.
Leaf mold: Decomposed leaves add nutrients and valuable organic matter to the soil. To make your own leaf mold, chop up leaves in the fall, moisten them, and then store them in a pile or pen over the winter. In the spring, stir and moisten, adding a few shovels full of compost or soil. It may take a year or more to go from dry leaves to leaf mold, but it’s worth the wait.
Limestone: This ground rock powder raises the pH of acidic soils and is also a calcium source. Lime is most effective when tilled into the soil. It also improves the texture of clay soil.
Manure: Animal manures add nutrients and organic matter and are most beneficial when composted prior to soil application. Fresh manure will “burn” plants with excess nutrients and salts, as well as introduce weed seeds into the garden.
Sand, coarse: This improves the drainage and texture of clay soil but must be added in substantial amounts to have the desired effect. Coarse sand usually is combined with compost or other organic matter to condition heavy clay; a typical recommendation is 3 to 4 inches of organic matter and 1 to 2 inches of coarse sand spread over the garden surface and dug into the top 8 to 10 inches of the soil.
Topsoil: Because of the expense, purchased topsoil is usually a replacement for existing soil rather than an amendment. Use it to create raised beds on top of poor soil sites.
In the long run, “feeding” your soil a regular diet of organic amendments such as compost will repay your efforts with healthier, more bountiful, more beautiful plants. As the health of your soil improves, you’ll find that your plants need less fertilizer and suffer from fewer pest and disease problems. Even if you never achieve soil perfection, you can create soil conditions that are perfect for your plants.
If You Need Help
* To learn about the characteristics of soils in your area, refer to the Natural Resources Conservation Service (NRCS). Your local NRCS office can give you information about common soil types and their features.
To get specific information about your soil, including recommendations for amending it, have the soil tested by your state’s Cooperative Extension office (Almanac.com/CoopExt). Request a soil-testing kit. Plan ahead–whether you mail it to the university for testing or drop it off at your county office, it may take a few weeks to get results.
Your test results typically will include a wealth of information: soil pH, the percentage of organic matter, levels of nutrients important to plants, and more. Be sure to ask for recommended organic products to use in improving your soil.
Amendments vs. Fertilizers
* Soil amendments may contribute nutrients to the soil; their main purpose is to improve the soil’s physical characteristics.
* Fertilizers add nutrients that benefit plant growth and typically have little effect on soil properties such as drainage and organic matter content.