Plant Zucchini in Zone 9a

Zone 9a averages 274 frost-free days, running from a last spring frost around March 1 to a first fall frost around November 30. Zucchini needs roughly 55 days from planting out to first harvest, so it uses about 20 percent of that window. Zucchini is a tender crop, which is what decides where in the window it belongs.

Because zucchini needs a head start, sow seed indoors around Feb 8, about 3 weeks ahead of the Zone 9a last frost. Transplants go out around Mar 15. Starting earlier than that in Zone 9a usually backfires: plants outgrow their cells and stall when they finally hit cold soil. At 55 days to harvest, a 274-day Zone 9a season has room for about 3 sowings, so stagger them rather than planting everything at once.

Yes. Sow zucchini by September 8 in Zone 9a. That is 83 days before the average first frost, which covers the 55 days to maturity plus about two weeks for the slower growth that comes with shortening days, plus a two week margin because frost kills zucchini outright.

One midsummer sowing of zucchini replaces the spring plants right as squash vine borer takes them out.