USDA Hardiness Zone 4B includes parts of Iowa, Michigan, southern Wisconsin, and upstate New York, with average annual minimum temperatures between -25°F and -20°F. The growing season stretches approximately 153 days from a last spring frost around May 1 to a first fall frost near Oct 1. This extra two weeks compared to Zone 4A opens the door to longer-season crops like winter squash and sweet corn. A late-spring cold snap is still common, so hardening off transplants and watching short-term forecasts remains essential. For a personalized forecast based on your specific zip code, use our free planting calendar. Browse individual plant guides for detailed growing instructions, or explore how USDA zones work to better understand your growing conditions.