Spring is the ideal time to check for earthworm activity. Wait until the soil temperature is at least 50F and soil moisture content at the surface is 20 percent or more. Using a shovel or spade, dig a cube of soil measuring roughly a foot on each side, and lay it next to the hole on the ground’s surface. Break it apart and look for earth worms. You’ll find at least ten earthworms per cubic foot in healthy soil. Repeat the procedure at several locations in your garden or schoolyard. If your soil’s average is fewer than ten worms per cubic foot, it’s time to add more organic matter like compost to your soil.