Answer: Asparagus beds are considered perennial in that the crowns do grow wider as the plants mature. Plan on spacing each crown 18" away from it's neighbor. You can plant other plants in the bed but I think it's easier to take care of an asparagus bed when it contains only asparagus.
Asparagus likes a nice, deep bed of rich soil, liberally amended with compost. Start by digging a foot-wide trench, 6"-8" deep and place a shovelful of compost every 15"-18". Set a crown on each heap of compost, and spread the roots evenly around. The crown (buds up) should be no more than 4" below the rim of the trench. Cover the crowns with a few inches of soil and compost mixed. Water the bed regularly while the plants get established. Weeds are a major problem for asparagus, so keep the area mulched and/or hoed to control them. Each spring, layer on more compost (8" is great) to feed the plants and keep them covered (they "climb" as the roots grow down into the soil).
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