Asparagus (perennial vegetable) is classed hardy perennial in the cited extension guidance. The timing rules below are relative to your local freeze dates — enter a location to turn them into calendar dates.
The rules this site applies
Method
Frost-relative window
Rule & reconciliation
Transplant outdoors
(plant crowns)
6–4 weeks before the median last spring freeze
Purdue: hardy — plant crowns 4–6 weeks before the last spring frost.
No direct-sow outdoors window: Home plantings start from 1-year crowns; seed-started asparagus adds a year and is not timed by the cited guide.
Variety assumption: A long-lived perennial; do not harvest the planting year, lightly the second year, fully from the third.
Hardiness classes: hardy = plant 4-6 wk before last spring frost; semi-hardy = 2-4 wk before; tender = after average last frost; very tender = at least 2 wk after. Table 2: fall planting at least 4-8 wk before first fall frost.