GreenlyWhat to plant in September in California
Worked out for 11 cities from their own weather and frost dates, by zone.
What to sow and plant in September in California, by zone: frost-free, highs above 82 °F (Los Angeles, San Jose and 6 more): zucchini, green beans, watermelon, pumpkin, sweet corn and 13 more; frost-free, highs of 72–82 °F (San Diego and Santa Barbara): broad bean, peas, onion, cabbage, broccoli and 32 more; frost-free, highs of 61–72 °F (San Francisco): broad bean, peas, onion, spinach, lettuce and 20 more.
In California, September is fall.
Frost-free, highs above 82 °F: Los Angeles, San Jose, Fresno, Sacramento and 4 more
In September, on average, these cities have highs of 84 to 96 °F and lows of 58 to 66 °F, 0.1 to 0.8 in of rain on 1 to 3 days; the day lasts 12 h 25 min to 12 h 30 min (on the 15th). A dry month: whatever is sown needs watering.
No frost in September in 10 years of data: frost-tender crops can go in too, if it is warm enough for them.
| How | What | Where |
|---|---|---|
| sow direct | Zucchini, green beans, watermelon, pumpkin, sweet corn, basil, bok choy, borage, chayote, corn, Florence fennel, kiwano, luffa, moringa, Napa cabbage, okra, peanut, soybean | Los Angeles, San Jose, Fresno and 4 more |
| start indoors, plant out in October | Cucumber | Los Angeles and Riverside |
| start indoors, plant out in October | Melon, achocha | Los Angeles |
Compared with August: no longer sown — tomato, bell pepper, eggplant and chili pepper.
Not starting in September: tomato (January, started indoors), bell pepper (January, started indoors), lettuce (November, sown direct), peas (November, sown direct) and spinach (November, sown direct) — dates for Sacramento.
Ready to harvest in September in Sacramento, if sown in the right month: chayote (April).
Frost-free, highs of 72–82 °F: San Diego and Santa Barbara
In September, on average, these cities have highs of 78 to 80 °F and lows of 59 to 65 °F, 0.4 to 0.6 in of rain on 2 days; the day lasts 12 h 24 min to 12 h 25 min (on the 15th). A dry month: whatever is sown needs watering.
No frost in September in 10 years of data: frost-tender crops can go in too, if it is warm enough for them.
| How | What | Where |
|---|---|---|
| sow direct | Broad bean, peas, cabbage, beet, parsley, cilantro, arugula, chamomile, chickpea, dill, mustard greens, okra | San Diego |
| plant sets | Onion, shallot | San Diego |
| start indoors, plant out in November | Broccoli, Brussels sprouts | San Diego |
| start indoors, plant out in October | Cauliflower, cucumber, melon, achocha | San Diego |
| sow direct | Zucchini, green beans, watermelon, pumpkin, sweet corn, basil, bok choy, borage, chayote, corn, Florence fennel, kiwano, luffa, moringa, Napa cabbage, peanut, soybean | all |
Compared with August: new — broccoli; no longer sown — tomato, bell pepper, eggplant and chili pepper.
Not starting in September: tomato (March, started indoors), bell pepper (March, started indoors), lettuce (October, started indoors) and spinach (November, started indoors) — dates for San Diego.
Ready to harvest in September in San Diego, if sown in the right month: broad bean (June), peas (July), cabbage (May), beet (July), zucchini (July), green beans (July), watermelon (June) and sweet corn (June).
Frost-free, highs of 61–72 °F: San Francisco
In September, on average, San Francisco has highs of 67 °F and lows of 57 °F, 0.1 in of rain on 1 days; the day lasts 12 h 28 min (on the 15th). A dry month: whatever is sown needs watering.
No frost in September in 10 years of data: frost-tender crops can go in too, if it is warm enough for them.
| How | What | Where |
|---|---|---|
| sow direct | Broad bean, peas, spinach, lettuce, radish, carrot, cabbage, broccoli, Swiss chard, beet, parsley, cilantro, arugula, chamomile, daikon, dill, kale, kohlrabi, mustard greens, parsnip | San Francisco |
| plant sets | Onion, shallot | San Francisco |
| start indoors, plant out in October | Cauliflower | San Francisco |
| start indoors, plant out in November | Leek, Brussels sprouts | San Francisco |
The same as in August.
Not starting in September: tomato (no month outdoors by these rules), bell pepper (no month outdoors by these rules), zucchini (no month outdoors by these rules) and green beans (no month outdoors by these rules) — dates for San Francisco.
Ready to harvest in September in San Francisco, if sown in the right month: broad bean (June), peas (July), spinach (July), lettuce (July), radish (August), carrot (July), cabbage (May) and broccoli (June).
How we work it out
For each city we use its average weather in September and the months after (highs, lows and rain for 2016–2025, ERA5 reanalysis via Open-Meteo) and its average frost dates. A crop starts in September if the month's mean temperature reaches the minimum soil temperature for germination on its card (we use the mean air temperature as a stand-in for the soil's) and if, over its first months (up to three), the average highs stay within its group's range, with no frost for crops that cannot take it. Crops started indoors count from the month they are planted out.
Temperature groups from Colorado State University Extension: cool-season crops prefer 60–80 °F and lose quality in heat; hardy ones grow in days as cool as 40 °F, semi-hardy ones from 40–50 °F (we use 50 °F); warm-season crops need days above 55 °F, and the most tender (tomato, pepper, eggplant, melon, watermelon, squash) above 60 °F, up to 95 °F. Crops the guide does not name go into the stricter group by their frost hardiness. Fava (broad) beans, which the guide does not name, count as hardy: hardy varieties are sown in fall and overwinter (RHS). Garlic and bulbs: a month before the first frost, and later only while the ground is not frozen (as on each city's page).
This is a general rule from averages: your garden can be a week or two earlier or later, and a greenhouse or a cold frame brings the season forward. Greenly works out the dates for your location.
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