Ontario · Growing Zone 4a
Gardeners in Thunder Bay, ON can expect the average last spring frost around May 28, and the first fall frost around September 25, based on historical Environment Canada frost data for the area. That gives Thunder Bay a frost-free growing season of roughly 120 days. Actual frost dates shift by a week or two year to year, so use this as a planning baseline rather than an exact guarantee, and always check your local forecast before moving tender plants outside.
Most warm-season crops (tomatoes, peppers, squash) need transplanting only after the last frost has passed, and are usually started indoors 6 to 8 weeks before that date. Cold-hardy crops (peas, lettuce, spinach) can often go in the ground a few weeks before the last frost. As Thunder Bay's first fall frost approaches in September, it's time to plan the last harvests for anything frost-sensitive still in the ground.
GrowBlock builds your whole season timeline around dates like these automatically, indoor seed starting, transplant windows, and harvest, tuned to Thunder Bay specifically.
Plan your Thunder Bay gardenAround May 28 on average, though it can vary by a week or two either way depending on the year.
Thunder Bay is in zone 4a, with a frost-free season of about 120 days.