Masterclass: Swiss Chard — Bay Area (Sunset + USDA)

Swiss Chard — Bay Area (Sunset 14–17; USDA 9–10)

Swiss chard thrives across the Bay Area, but the how depends on microclimate. We combine USDA 9–10 (cold‑hardiness) with Sunset 14–17 (our real day‑to‑day: fog, wind, length of season, summer highs). Sunset zones capture factors USDA doesn’t, so timing and variety choice track more precisely to coast vs. inland.

Here’s the plan: a Sunset+USDA timing matrix that shows when to sow/transplant and how to hedge against heat or fog; a weekly checklist to get from bed prep to steady harvests; IPM timing for leafminers and late‑season mildews; and five heirloom cultivars that perform in our region.

“GrowBot did some digging: quick, even growth beats most chard problems. Mulch + steady drip = fewer tough leaves, fewer miner scars.”

Sunset + USDA microclimate matrix (timing & tactics)

• Sunset 17 (fog belt; USDA ~10): Sow late summer–early fall; transplant Sep–Oct and late winter. Favor steady moisture, good airflow to limit mildew.

• Sunset 16 (thermal belts; USDA 9–10): Sow late summer–fall; spring is also reliable; provide light shade in early heat waves.

• Sunset 14–15 (inland with marine influence; USDA 9): Fall plantings excel; spring plantings end earlier in heat — mulch and harvest younger leaves.

Weekly checklist (example, fall start)

• Week 0: Clear bed; add 1–2” compost; set drip; pre‑irrigate; lay 2–3” mulch.

• Week 1: Direct‑sow ½” deep or transplant; install light shade cloth if warm inland.

• Week 2–3: Thin to 12–18” spacing; begin light harvests of baby leaves.

• Week 4+: Harvest outer leaves twice weekly; top‑dress with compost if growth slows.

Targeted IPM timing

• Leafminers: peak when nearby beets/spinach host; remove mined leaves promptly; row cover for seedlings; treatment seldom required in home beds.

• Powdery mildew (late season): water mornings, increase spacing/airflow; choose tolerant varieties; fungicides rarely needed in home settings.

Heirloom Varieties for the Bay Area

• ‘Lucullus’ — classic heirloom; broad leaves, steady fall–winter harvests; tolerates cool nights.

• ‘Fordhook Giant’ — vigorous, large leaves; dependable regrowth inland with mulch.

• ‘Rhubarb Chard’ — red ribs; strong performance in cool shoulder seasons.

• ‘Perpetual Spinach’ (leaf beet) — mild flavor; excels near coast with steady moisture.

• ‘Rainbow / Five‑Color Silverbeet’ — heirloom‑derived mix; diverse stems aid succession picking.

Sources & Further Reading

• Sunset Climate Zones explainer

• UC IPM — Vegetable leafminers; Powdery mildew on vegetables

• Masterclass: Tomato — Bay Area

• Premium Downloads