How-To Project: Testing Soil Drainage and Texture
by National Gardening Association Editors
Your soil's texture and drainage determine the kinds of plants you can grow most successfully and influence how you care for your plants.
Texture describes the relative amounts of large, medium, and small particles called sand, silt, and clay in the soil. Water and nutrients move quickly through soil that has a sandy texture because more space exists between the larger soil particles. Small clay particles, on the other hand, pack together tightly so water does not drain as quickly through them.
Tools and Materials
- Water source
Squeeze a handful of soil. Grab a handful of moist soil and squeeze it. Clay soil is slippery and oozes between your fingers. It holds its shape when you release it. Sandy soil feels gritty and falls apart easily. Loam soil holds together, but falls apart when you poke it.
Make a ribbon in your hand. Soils that won't form a ribbon when rolled between your thumb and fingers contain at least 50 percent sand and only a little clay. Ribbons that break before reaching 2 inches long contain about 25 percent clay. If you can squeeze out a ribbon 2 to 3-1/2 inches long, your soil contains at least 40 percent clay.
Dig a hole. Another way to determine the texture of your soil is to check how fast water drains through it. Dig a hole 1 foot deep by 1 foot wide. Fill the hole with water and record how long it takes for the water to completely drain. The ideal time is between 10 and 30 minutes. If it drains in less than 10 minutes, the soil is drought-prone and most suitable for plants that need dry or well-drained soil. If it takes 3 to 4 hours, your soil is poorly drained, due either to a large percentage of clay or an impermeable layer of minerals below the surface that blocks water movement.
If you live where rainfall provides most of the water plants need, choose trees, shrubs, and perennial plants that thrive in your particular soil.
If you live where irrigation is a necessity, apply water to clay soils very slowly but long enough for the water to soak in deeply. Then withold water until you're sure it's needed again. Conversely, if your soil is sandy, water for less time but more frequently.
Add organic material, such as compost, manure, or shredded leaves to sandy soil to improve its ability to hold water and to clay soil to help it drain more quickly.
Photography by Suzanne DeJohn/National Gardening Association