Double Digging is a labor-intensive but very thorough method of digging a bed deeply. Dig a 9-inch trench across the bed, stockpiling soil on a tarp. With a pitch-fork, loosen the trench bottom to 9-inches deep, then top with compost of some sort. Dig a second trench, tossing its soil into the first. Loosen, add compost, and continue to the end of the bed. Fill the last trench with the original soil you set aside. Then rake to the level of the soil. The soil will be higher than before, but it will eventually settle.