When to plant asparagus in zone 6a
In zone 6a, the average last spring frost is Apr 28 and the first fall frost is Oct 15. Here is asparagus's whole year, counted from those dates.
Choose a permanent bed with full sun, deep loose soil, and sharp drainage. Cornell prefers a pH near 7 and says to avoid frost pockets, because a late frost can kill emerged spears. Clemson prepares the bed with compost and aims for pH 6.0–6.5.
Plant disease-free 1-year-old crowns. Cornell's window is 4–6 weeks before the average last frost; the calendar uses the middle of that range. Set crowns 18–24 inches apart in a trench about 8 inches deep (5 inches for Jersey series), spread the roots, and cover with 1–2 inches of soil. Fill the trench in gradually as the ferns grow.
Clemson sets crowns 15–18 inches apart and 6–8 inches deep, a bit tighter and sometimes shallower than Cornell. Do not harvest the planting year. Let the ferns die back on their own before you cut them.
Clemson says to wait until the third or fourth year for a light harvest of 3–4 weeks, and to take spears at 6–8 inches before the tips open. Cut or snap at the soil surface. A Cornell Cooperative Extension summary counts about 2 years from planting crowns to a crop, so the two extensions do not agree on the first picking year.