San Francisco is effectively frost-free — here's how the garden calendar works when cold isn't the constraint.
Medians from 1991–2020 climate normals for the area. "Safe" means frost past that date happens only about one year in ten. Your exact garden can still run days either way with elevation and terrain — check your own ZIP with the frost date lookup.
In zone 10b, the limiting factor is summer heat, not winter cold. The most productive stretch for classic vegetables runs fall through spring: sow cool-season crops (lettuce, broccoli, carrots, greens) from October into February, and plant warm-season crops in late winter so they fruit before peak heat, with a second round in late summer. Crop-by-crop guidance for frost-free zones lives in our zone 10 growing guides.
Rarely to never — San Francisco sits in USDA zone 10b, where the average winter minimum stays above freezing damage thresholds. Gardening here is scheduled around heat and rainfall instead of frost.
Flip the standard calendar: warm-season crops (tomatoes, peppers, squash) grow nearly year-round but struggle in peak summer heat, so plant them in late winter and again in late summer. Cool-season crops (lettuce, broccoli, carrots) belong in the mildest stretch, typically October through March.
USDA zone 10b on the 2023 Plant Hardiness Zone Map. Zone ratings describe average winter minimum temperature, which is why frost planning barely applies here.