Sweet corn (warm-season grain vegetable) is classed tender 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
Direct-sow outdoors
2–4 weeks after the median last spring freeze
UGA: wait until at least two weeks after the last average killing frost. Purdue lists corn as tender (after last frost) and UNH keys sowing to 60°F soil; the later UGA rule is used.
No start seeds indoors window: The cited guides time sweet corn by direct seeding only.
Variety assumption: Assumes a mid-season hybrid (about 70–85 days; Penn State lists 80).
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.