A soil sampling tube, also called a soil coring tool, is used to look at the soil under your plants. It consists of a metal tube sharpened at one end, with a handle at the other end forming a T. The tube is shoved into the soil. When withdrawn, a core of soil is trapped in the tube. The core is visible, and can be removed, through a wide slot cut in the side of the tube.
Sampling tubes have three primary uses.
They allow you to see how far water is penetrating into the soil and how wet the soil is. When water is applied, it wets the soil to saturation on the surface, then that saturated zone (called a wetting front) sinks deeper into the soil. The more water you apply, the deeper the zone goes.
An hour or so after watering dry soil, use a sampling tube to see how far the wetting front has penetrated. It should reach to the bottom of the root zone of the plants you are watering.
A sampling tube collects samples for soil tests quickly and easily. Take a sample, then remove the part of the core you want (usually from 6 inches deep almost to the surface) for testing.
Sampling tubes show you a soil profile. See what your subsoil looks like, how deep your topsoil is, and whether the soil is layered. If drainage is a problem in one part of your garden, check a core a foot or so deep to see if it has any dramatic changes in soil texture. Water doesn’t move easily from one texture to another—from sand to clay or clay to sand—so layers of soil impede drainage.
Maintain your sampling tube by cleaning it, then spraying or wiping it with oil after each use.