What is double-digging? Loosening the soil more than 12 inches down to create conditions under which plants' roots thrive.
How to double-dig: Begin at one end of the bed and dig a 1-foot-wide by 1-foot-deep trench across the bed's width, placing the excavated dirt in a wheelbarrow. Next, work a garden fork into the floor of the trench and slowly rock it back and forth to loosen the soil. Continue until the soil in the excavated area is loosened. Dig a second, similar-size trench next to the first, this time placing the excavated soil in the first trench. Loosen the soil at the bottom of the second trench with the garden fork. Dig another trench and backfill the second trench, loosen the bottom of the third trench, and continue this process until you reach the end of the bed. Fill the last trench with the soil excavated from the first.
Why you should double-dig: Carrots, potatoes, beets, and other root crops need deep, loose soil to grow well. More important, double-digging is the first step in creating the most productive garden bed possible, insists John Jeavons, author of How to Grow More Vegetables (Ten Speed Press, revised 2002). "Double-digging adds air deep into the soil and enables roots to grow and the microbes to create good soil structure," Jeavons says. This is, no two ways about it, a labor-intensive approach. But if the soil where you want your garden is very dense or hard-packed, making the effort to do this will pay you back handsomely as your garden grows.