Plant Kale 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. Kale needs roughly 60 days from planting out to first harvest, so it uses about 41 percent of that window. Kale is a hardy crop, which is what decides where in the window it belongs.

Because kale needs a head start, sow seed indoors around Mar 24, about 6 weeks ahead of the Zone 4b last frost. Transplants go out around Apr 21. Starting earlier than that in Zone 4b usually backfires: plants outgrow their cells and stall when they finally hit cold soil.

Yes. Sow kale by August 13 in Zone 4b. That is 46 days before the average first frost, which covers the 60 days to maturity plus about two weeks for the slower growth that comes with shortening days, minus the roughly 28 days kale keeps going once light frost arrives.

Kale is usually the last thing standing in the garden. Frost converts its starch to sugar, so the flavour improves after the first freeze.