Here are a few tips from Guthrie County ISU Extension and Outreach when harvesting asparagus:

Asparagus plants should be allowed to become well established before any spears are harvested. No spears should be harvested during the first growing season and they can be harvested over a 3-4 week period during its second growing season. Asparagus plantings can be harvested until early to mid-June and should be removed by cutting or snapping the spears at ground level when they reach a height of 6-8 inches.