Plant Potatoes in Zone 10a

Zone 10a averages 323 frost-free days, running from a last spring frost around January 31 to a first fall frost around December 20. Potatoes needs roughly 90 days from planting out to first harvest, so it uses about 28 percent of that window. Potatoes is a half-hardy crop, which is what decides where in the window it belongs.

Potatoes handles cold soil, so there is no reason to wait for the frost date. Direct sow around Jan 17, roughly 2 weeks before the Zone 10a 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 90 days to harvest, a 323-day Zone 10a season has room for about 3 sowings, so stagger them rather than planting everything at once.

Yes. Sow potatoes by September 17 in Zone 10a. That is 94 days before the average first frost, which covers the 90 days to maturity plus about two weeks for the slower growth that comes with shortening days, minus the roughly 10 days potatoes keeps going once light frost arrives.

A fall potato crop works in zone 8 and warmer, planted in late summer from certified seed pieces that have broken dormancy.