Yet frost dates are widely misunderstood.
The average last spring frost, after which frost becomes increasingly unlikely as spring turns to summer.
This is the most important thing to understand about frost dates.
It is designed to tell you which perennial plants will survive your winters, not when to plant vegetables.
Most publish frost dates or planting calendars by county or region, tuned to local conditions.
On clear, still nights, it flows downhill and pools in low spots, much like water.
Beans, corn and squash need warm soil to germinate, and seeds can rot in cold, wet ground even after the frost date has passed.
Step-by-step advice, charts and free garden calculators at Garden Voila.