San Francisco, CA

San Francisco gardening operates in a temperate maritime climate where the dominant constraint is not frost but marine layer fog and moderate temperatures. Winter lows recorded in NOAA data range from 35 to 40°F, so frost is possible on clear nights, but it rarely reaches intensity that damages established plants or prevents year-round growing. The real limitation is the fog belt that dominates May through August, bringing clouds, wind, and cool mornings that slow growth and ripening of heat-loving crops. This climate paradoxically favors cool-season vegetables: lettuce, kale, chard, brassicas, and peas produce vigorously in these months when most of the country is heat-stressed. Mediterranean crops like figs and rosemary thrive here precisely because San Francisco's maritime climate mirrors their native conditions. Heat-lovers like tomatoes, peppers, and eggplant require careful site selection and often succeed better when planted late (June or July) for fall harvest rather than early spring. The 365-day growing season is both asset and puzzle: something grows every month, but gardeners must match crops to seasonal light and temperature patterns rather than following the calendar triggers that work inland.

Marine layer fog from May through August reduces direct sunlight, slowing photosynthesis and ripening. Tomatoes and peppers often remain green or partially ripe by late fall if planted in marginal microclimates or exposed to persistent cloud cover. This forces precision in site selection and variety choice that gardeners new to San Francisco frequently underestimate. Frost, though rare and usually light, does occur on clear winter nights when temperatures approach the 35-40°F minimum. Tender crops like basil and young eggplant can be damaged if an unexpected cold snap strikes in late December or early January. Wind is a secondary stressor: the channeled winds through San Francisco's neighborhoods can desiccate young seedlings and break stakes on young tomato plants. Soil varies significantly by neighborhood; some areas have clay-heavy, poorly draining soil that requires amendment.

Site heat-loving crops deliberately. A south-facing wall or corner that reflects heat from the structure can warm soil and air enough to ripen peppers reliably by November, whereas an open, fog-exposed bed may not. Use mulch and windbreaks to moderate the temperature swings and wind stress. Second, reverse your seasonal mindset: instead of fighting the fog season, shift intensive production of cool-season crops to May through August. Plant lettuce, chard, kale, and beets in May or June for peak summer harvest when inland gardeners battle 95°F heat. Third, plant tender crops for fall harvest rather than spring. Late May or June planting of tomatoes and peppers into warming soil often outperforms early spring planting that battles cool, cloudy weather and damping-off disease; the crop matures into fall's more stable weather instead of pushing through fog season.