Seattle in September: what to plant
Over the last 5 years, September in Seattle has run 13.0–21.1°C with about 50 mm of rain across the month. Here is what weather like that will carry to harvest.
Everything above is a five-year average. In the game it is this — the weather Seattle is actually having, today.
Grow one in Seattle's weather right now →❄️ No sub-zero nights in September in the last 5 years — frost is not the limiting factor here.
🗓️ This month sits inside the frost-free window. Average last spring frost around Mar 1, first autumn frost around Dec 9 — roughly 283 frost-free days. Sow tender crops after the last frost date and make sure they finish before the first.
☀️ About 9.2 h of sunshine a day this month. Within the month it cools by about 3.3°C from the first ten days to the last — the window for autumn sowings is opening.
Sow this month — when would you harvest?
Assuming you sow in mid-September, then adding up the warmth Seattle usually gets, one day at a time — which is why some of these run past the end of the month.
| Crop | Days | Harvest around |
|---|---|---|
| 🌿 Garlic chives | 238 | May 10 |
| 🥬 Napa cabbage | 229 | May 1 |
| 🥕 Parsnip | 244 | May 16 |
| 🧅 Onion | 260 | Jun 1 |
⏳ Too late this month: Zucchini, Green Beans, Amaranth greens, Sunflower, Marigold, Potato, Cauliflower, Strawberry would still be in the ground when the first frost arrives (around Dec 9). Sow them earlier in the year, or grow them under cover.
🌡️ Chili Pepper, Yardlong bean, Bitter melon, Luffa, Winter melon, Aubergine, Okra never accumulate enough heat outdoors in Seattle — not in any month. Locally these need a greenhouse or a warm windowsill.
Best crops to sow now
They are all ideal for this month — the only real difference is how long each one takes, so pick whatever you want to eat.
- 🥒 Zucchini about 93 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🥢 Green Beans about 86 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🌿 Amaranth greens about 79 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🌻 Sunflower about 111 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🏵️ Marigold about 60 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🥔 Potato about 90 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🌿 Garlic chives about 71 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🥬 Cauliflower about 73 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🥬 Napa cabbage about 65 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🍓 Strawberry about 58 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🥕 Parsnip about 99 days to harvest Recent mean 17.0°C — right in the sweet spot
- 🧅 Onion about 88 days to harvest Recent mean 17.0°C — right in the sweet spot
Leave these for another month
- 🌶️ Okra — Recent mean 17.0°C is too cold (ideal 20–33°C)
- 🍆 Aubergine — Recent mean 17.0°C is too cold (ideal 18–32°C)
- 🍈 Winter melon — Recent mean 17.0°C is too cold (ideal 18–32°C)
Other months in Seattle
📍 Somewhere else? Look up your own city →
Temperature and rainfall come from Open-Meteo's historical observations for Seattle, averaged day by day over the last 5 years. Whether a crop finishes in time is worked out from its own starting temperature and heat requirement — those numbers are listed on each crop page if you want to check them.