Masterclass: September Planting — Bay Area (Sunset + USDA)

September Planting Masterclass (Bay Area)

September is the Bay Area hand-off from warm-season to cool-season crops. The trick is matching your microclimate. Sunset zones account for fog, summer highs, wind, and humidity — factors USDA zones ignore — so they’re a better steering wheel for us (we still include USDA as a cross-check). Coastal fog belts (Sunset 17) can transplant brassicas without heat stress; coastal thermal belts (16) enjoy a balanced cool; inland-marine zones (14–15) may still have warm afternoons that require seedling protection. Local Master Gardener calendars align: clear summer beds, refresh soil with compost, and plant cool-season vegetables through September; for broccoli transplants mid-September, start seeds roughly six weeks earlier.

Inside the Masterclass you’ll get precise sow/transplant windows for Sunset 17/16/14–15, a week-by-week checklist, and pest defenses (row cover + Bt for cabbageworms; slug control in fog belts). We also include a fridge-ready printable and heirloom varieties that shine in fall beds (‘Di Cicco’ broccoli, ‘Bloomsdale Long Standing’ spinach, ‘Chioggia’ beet). Consider this your September field manual—built for Bay Area nuance. Alameda, San Mateo/SF, and Santa Clara guidance underpins the timing below.

Microclimate timing (Sunset + USDA cross-reference)

• Sunset 17 (coastal/fog belt; USDA ~10): Direct-sow salads/roots all month (lettuce, spinach, radish, beet, carrot). Transplant broccoli/cauliflower now; expect high slug pressure after foggy mornings — use iron-phosphate baits and hand-picking. Start peas late month if beds are cool.

• Sunset 16 (coastal thermal belts; USDA 9–10): Transplant brassicas early September; steady direct-sowing of greens and roots all month. Peas from mid- to late month. Use light shade cloth on >80°F days to prevent lettuce tipburn.

• Sunset 14–15 (inland with marine influence; USDA 9): Transplant brassicas early; sow carrots/beets/radish through late month. Seed lettuce evenings during warm spells; provide afternoon shade for seedlings during heat.

Weekly checklist (September)

• Week 1: Pull spent tomatoes/cukes. Top-dress 1–2” compost; check irrigation.

• Week 2: Transplant broccoli/cauli/cabbage. Install row cover over brassicas to block moths.

• Week 3: Direct-sow carrots, beets, radishes; succession lettuce/spinach.

• Week 4: Sow peas (zone-appropriate). Refresh 2–3” mulch ahead of first fall rains.

Pests & diseases (what’s active now)

• Imported cabbageworm (white butterfly): exclude with floating row cover; spot-treat small caterpillars with Bt or spinosad.

• Flea beetles: keep soil evenly moist; use lightweight row cover on young brassicas.

• Slugs/snails (fog belts): hand-pick at dusk; use iron-phosphate baits.

Deeper growing guidance

• Soil: Aim for friable, organic-rich beds; maintain even moisture to prevent radish/lettuce bitterness.

• Succession: Sow small patches of lettuce/spinach/radish weekly for steady harvests.

• Companion notes: Interplant alliums with carrots/beets; tuck calendula to attract beneficials (optional).

Heirloom Varieties for the Bay Area (fall focus)

• Broccoli ‘Di Cicco’ — reliable, staggered side-shoots.

• Spinach ‘Bloomsdale Long Standing’ — handles cool shoulder seasons.

• Beet ‘Chioggia’ — fast, sweet roots for fall harvest.

Downloads

• [Printable PDF] September microclimate calendar + weekly checklist

“GrowBot did some digging… If cabbage butterflies are fluttering, it’s already egg-laying time. Row cover today saves you from caterpillar confetti later.”