Plant Tomatoes 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. Tomatoes needs roughly 75 days from planting out to first harvest, so it uses about 27 percent of that window. Tomatoes is a tender crop, which is what decides where in the window it belongs.

Because tomatoes needs a head start, sow seed indoors around Jan 11, about 7 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 75 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 tomatoes by August 19 in Zone 9a. That is 103 days before the average first frost, which covers the 75 days to maturity plus about two weeks for the slower growth that comes with shortening days, plus a two week margin because frost kills tomatoes outright.

A second tomato crop only works where the first fall frost is late enough to finish it, which in practice means zone 9 and warmer.