Zone 4a Frost Dates & Planting Calendar

What zone 4a actually tells you

The 2023 USDA Plant Hardiness Zone Map puts a place in zone 4a when the coldest night of the year averaged -30 to -25°F (-34.4 to -31.7°C) over 1991–2020. The zone says which perennials survive the winter, not when to plant in spring.

Across the 111 NOAA stations behind zone 4a ZIP pages, the median 50% last spring frost is May 12 and the median first fall frost September 28; the last frost alone ranges from May 2 to June 9 from one station to another.

Frost dates answer the planting question, and they are read from the nearest NOAA station, not from the zone. The zone 4a ZIP codes here lie in 17 states; pick your own ZIP code below, or look up the zone of any ZIP code.