Raised beds warm up quickly and can speed up maturity dates.
"Double digging" is a good way to recycle good topsoil. Dig down at least "6." Set the topsoil (about first 3"-4") aside and add any clumps of grass, or weeds if they are seed-free, upside down in the bottom of the trench before filling.
Fill trench with a mixture of dug soil and compost or manure. Toss out larger chunks of clay or rocks.
When refilling the trench, raise the top of the bed at least 3", ideally 6" above the soil line. It warms up the soil faster, improves drainage, and helps roots get better established.
Virginia Extension Service advises not to dig too far down when planting asparagus crowns. "Yields improve dramatically when crowns are set at a depth of 5 to 6 inches -- not the commonly advised 12 inches. Contrary to the standard practices of deep planting and not harvesting for up to three seasons, recent studies show that harvesting shallow- planted asparagus after the first year boosts yields 40 percent over three years." That is, if the rodents don't get to them first!