Be patient. Asparagus plants can live fifteen to twenty years or longer. To increase your yield make sure that your asparagus plants receives eight hours of direct sunlight a day. The asparagus plants need to be fertilized with a general 10-10-10 fertilizer once a year. Also, apply bone meal to the asparagus bed after the first killing frost in the fall. The asparagus bed should receive an inch of water per week.

You mention you can see the crowns however the crown should be planted six to eight inches deep so they should not be visible.

The following article provides more information on growing asparagus: Growing asparagus in home gardens | UMN Extension

Thank you for your question and have a great gardening experience.