Asparagus is a perennial vegetable. You eat the stalk that emerges before it grows very tall, similar to rhubarb. I think you let it grow without harvesting the first year to establish root system. Thereafter you harvest the stalks as they reach adequate height. You would not need to leave room for additional plantings in following years.
Your county extension office may have publications available to tell you more. WA Extension has a publication for commercial asparagus crop establishment at: http://farm-mgmt.wsu.edu/PDF-docs/irrigated/eb1779.pdf