…“What’s in your soil?
In fact, half of the ideal loam consists of elements we don’t consider to be soil at all: water (25%) and air (25%). But the solid components determine how much air and water the soil can hold. Organic matter — humus (decaying plants) and soil organisms — may only account for about 5% of your garden soil. The balance is mineral particles of varying size, including sand (largest), silt (finer), and clay (finest). The more sand, the more air the soil will hold, but water will drain away too quickly if sand content is too high. Silt and clay hold water more effectively, but too much and there may be no room for the air which is essential for root respiration and nutrient exchange.
And so, when we asses soil for gardening, we’re looking for an ideal balance of elements.
When sand, silt, clay, and humus are each present in roughly equivalent quantities, you have a good loam to bring a smile to any gardener’s face. Once you discover what’s in a spade-full of your own dirt, you can choose to add various amendments to make conditions more hospitable for your garden’s intended occupants. Or to take another approach, you can choose your plantings based on your soil. Perennials and fruit trees like sandier (though still moist) soil, while many vegetables such as melons, squash, and brassicas including broccoli, cabbage, and brussels sprouts will do well in denser, wetter soil. Talk to other local gardeners who may have similar soil.
How to get a good soil sample
Choose a representative spot in a garden bed or planned planting site. You may wish to test a few different areas, as results can vary even within a small area. Remove any plants and debris from the surface. Use a shovel to remove a chunk of soil about 6-8 inches deep and set it aside. Now you are ready to scoop your testing material into a container. Insert your trowel vertically along the edges of the hole to obtain a cross-section of topsoil. This is the crucial layer for most garden plants, especially annuals. Mix up the resulting strips of soil until you have a fairly uniform substance.
Use your senses
Rub some dirt between your fingers and take a close look. Is it gritty, crumbly, sticky, fluffy, silky? You will begin to understand the texture and composition of your garden just by looking and touching. Next, bring a handful near your face and take a deep breath. How does it smell? If your soil is fertile with an abundance of healthy microorganisms, it will smell pleasant and “earthy”. Any offensive odor indicates your soil is putrefying with anaerobic bacteria and needs aerating — just like tender roots, the “good” bacteria need oxygen to thrive.
Test 1: Soil Composition
Trowel four inches of soil into a quart-sized glass mason jar. Fill the jar with water up to the neck, tightly screw on the lid, and shake vigorously. Now set the jar aside for at least 24 hours. When you return the next day, the sample will have settled into visible layers showing the proportions of your soil components. Sand goes quickly to the bottom, with silt just above, then clay, then organic matter. Bits of undecomposed plant matter will float on top. If the water is still opaque with dissolved clay, try leaving the jar in a dark place (to prevent algae growth) for a few more days. Measure each layer.