GreenlyWhat to plant in September in the Pacific Northwest
Worked out for 11 cities from their own weather and frost dates, by zone.
What to sow and plant in September in the Pacific Northwest, by zone: frost-free, highs of 72–82 °F (Portland, Boise and 8 more): garlic, broad bean, peas, onion, spinach and 15 more; frost-free, highs of 61–72 °F (Seattle): broad bean, peas, onion, spinach, lettuce and 16 more.
In the Pacific Northwest, September is fall.
Frost-free, highs of 72–82 °F: Portland, Boise, Spokane, Salem and 6 more
In September, on average, these cities have highs of 72 to 82 °F and lows of 49 to 56 °F, 0.4 to 2.8 in of rain on 3 to 9 days; the day lasts 12 h 32 min to 12 h 38 min (on the 15th).
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 |
|---|---|---|
| plant cloves | Garlic | Boise, Spokane, Idaho Falls and 3 more |
| sow direct | Broad bean, peas, cabbage, beet, parsley, cilantro, arugula, chamomile, dill, mustard greens | Portland, Spokane, Salem and 5 more |
| plant sets | Onion | Portland, Spokane, Salem and 5 more |
| start indoors, plant out in October | Spinach | Portland, Spokane, Salem and 5 more |
| start indoors, plant out in October or sow direct | Lettuce, kohlrabi | Portland, Spokane, Salem and 5 more |
| sow direct | Carrot, kale, parsnip | Olympia and Tacoma |
| start indoors, plant out in November or sow direct | Broccoli | Portland, Salem, Olympia and 3 more |
| start indoors, plant out in October or sow direct | Swiss Chard | Portland, Salem, Olympia and 3 more |
| sow direct | Chickpea | Portland, Salem, Olympia and 3 more |
| plant sets | Shallot | Portland, Salem, Olympia and 3 more |
| plant bulbs | Crocus, daffodil, hyacinth, tulip | Boise, Spokane, Idaho Falls and 3 more |
Compared with August: new — garlic, broad bean, peas, onion, spinach, lettuce, carrot, cabbage and 18 more; no longer sown — zucchini, green beans, watermelon, pumpkin, sweet corn, basil, bok choy, borage and 10 more.
Not starting in September: tomato (March, started indoors), bell pepper (March, started indoors), zucchini (April, started indoors) and green beans (June, sown direct) — dates for Eugene.
Ready to harvest in September in Eugene, if sown in the right month: zucchini (July), green beans (July), sweet corn (June), basil (July), bok choy (July), borage (July), corn (June) and Florence fennel (June).
Frost-free, highs of 61–72 °F: Seattle
In September, on average, Seattle has highs of 71 °F and lows of 54 °F, 3.1 in of rain on 10 days; the day lasts 12 h 38 min (on the 15th).
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, lettuce, carrot, cabbage, broccoli, Swiss chard, beet, parsley, cilantro, arugula, chamomile, chickpea, dill, kale, kohlrabi, mustard greens, parsnip | Seattle |
| plant sets | Onion, shallot | Seattle |
| start indoors, plant out in October | Spinach | Seattle |
Compared with August: new — spinach, carrot and parsnip; no longer sown — cauliflower, zucchini, green beans, sweet corn, basil, bok choy, borage and corn.
Not starting in September: tomato (March, started indoors), bell pepper (March, started indoors), zucchini (April, started indoors) and green beans (June, sown direct) — dates for Seattle.
Ready to harvest in September in Seattle, if sown in the right month: broad bean (June), peas (July), cabbage (May), beet (July), zucchini (July), green beans (July), sweet corn (June) and parsley (July).
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.
- Moon planting calendar for September 2027
- What to plant in September: all climates
- Gardening in the United States: guide by region
