Plant Spinach in Zone 4b

Zone 4b averages 146 frost-free days, running from a last spring frost around May 5 to a first fall frost around September 28. Spinach needs roughly 45 days from planting out to first harvest, so it uses about 31 percent of that window. Spinach is a hardy crop, which is what decides where in the window it belongs.

Spinach handles cold soil, so there is no reason to wait for the frost date. Direct sow around Mar 31, roughly 5 weeks before the Zone 4b last frost, as soon as the ground is workable. Sowing at the last frost instead costs you the coolest and best part of the season. At 45 days to harvest, a 146-day Zone 4b season has room for about 2 sowings, so stagger them rather than planting everything at once.

Yes. Plant spinach between August 17 and August 31 in Zone 4b, roughly 6 to 4 weeks before the average first frost, so it roots before the ground freezes.

Spinach sown 4 to 6 weeks before the first frost sizes up, stalls through winter under a row cover, and restarts weeks before anything can be sown in spring.