Zone 4b Frost Dates & Planting Calendar

What zone 4b actually tells you

The 2023 USDA Plant Hardiness Zone Map puts a place in zone 4b when the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020. The zone says which perennials survive the winter, not when to plant in spring.

Across the 206 NOAA stations behind zone 4b ZIP pages, the median 50% last spring frost is May 8 and the median first fall frost October 1; the last frost alone ranges from April 22 to June 20 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 4b ZIP codes here lie in 17 states; pick your own ZIP code below, or look up the zone of any ZIP code.