When to Plant Onions in Washington (2026 Guide)
Onions are a vital vegetable for every gardener in Washington, offering the promise of delicious flavor and long-term storage. Planting onions can be a rewarding endeavor, but knowing when to plant is crucial to ensure their success. Understanding the frost dates in your area is key, as onions thrive in a long growing season and need specific conditions to develop properly.
In Washington, the growing conditions vary by region, with the last spring frost date ranging from April 9 in Zone 6b to May 6 in Zone 5b. For gardeners in cities like Arlington and Bellevue, a frost-free season of approximately 200 days means onions can be sown early in the year. Those in Olympia, with a shorter growing season, should plan their planting times accordingly to maximize their onion yields.
Selecting the right onion variety based on day length is critical for success in Washington. Long-day onions, like 'Walla Walla,' flourish in the northern parts of the state, where longer daylight hours are available. Conversely, short-day varieties may struggle if planted in the incorrect latitude, leading to disappointing results. By following the recommended planting schedules, you can cultivate a bountiful onion harvest that lasts for months.
Planting Schedule by USDA Zone in Washington
| Zone | Indoor start | Transplant out | Direct sow | Harvest |
|---|---|---|---|---|
| Zone 6b | Start February 15 – March 1, ~6–8 weeks before April 10 | Transplant outdoors April 10 – April 25, after last frost | Direct sow April 15 – May 1, after last frost | Harvest late August – early September, before October 26 |
| Zone 6a | Start February 25 – March 10, ~6–8 weeks before April 20 | Transplant outdoors April 20 – May 5, after last frost | Direct sow April 25 – May 10, after last frost | Harvest late August – early September, before October 19 |
| Zone 5b | Start March 10 – March 25, ~6–8 weeks before May 6 | Transplant outdoors May 6 – May 20, after last frost | Direct sow May 1 – May 15, after last frost | Harvest late August, before October 3 |
Onions Planting Windows in Washington
- Indoor start: For Washington growers, start onion seeds indoors between February 15 and March 25, depending on your local frost dates.
- Transplant outdoors: Transplant your onion seedlings outdoors between April 10 and May 20 for optimal growth and harvest timing.
- Harvest: Harvest occurs between late August and early September, ensuring you pull your onions before the first fall frost on October 3.
Common Mistakes Growing Onions in Washington
- One common mistake in Washington is planting onions too late in the season, especially in areas with shorter growing seasons like Zone 5b. If you miss your window, you risk having small or bolted bulbs come harvest time.
- Gardeners in Washington often underestimate the importance of selecting the right onion variety based on day length. Planting short-day onions in northern areas can lead to poor yield and disappointing results, making proper variety selection critical.
- Ignoring soil conditions is another mistake. Onions prefer well-draining soil rich in organic matter. It’s essential to consider the clay or alkaline soils common in certain parts of Washington, as they can negatively affect growth and bulb size.
- Late spring frosts can wreak havoc on young onion plants in Washington, especially in areas near the mountains. Failing to cover your young plants or giving them enough space can lead to frost damage, stunting their growth significantly.
- Some Washington gardeners may overwater their onions, especially during the cooler, misty months. Excessive moisture can lead to root rot and disease; understanding the local climate can help tailor your watering schedule to keep onions healthy.
Frequently Asked Questions
What if I'm in a cold pocket of Washington?
If you're in a colder area, consider starting onions indoors earlier in February. Pay careful attention to local frost dates to avoid planting seedlings too early outdoors. You might also want to choose hardy onion varieties that can withstand cooler temperatures.
Can I still plant onions in May?
In most parts of Washington, planting onions in early May may limit your harvest success, especially in Zone 5b due to the shorter growing season. However, if you choose fast-maturing, short-day varieties, you will likely still obtain a modest yield before the summer heat.
How do I know when to water my onions?
Water your onions when the soil dries out a few inches below the surface but avoid overwatering. Signs that they may need water include wilting tops and dry soil conditions. Monitor the weather; if rainfall is abundant, you may need to reduce your watering frequency.
What are some signs that my onions are ready to harvest?
Your onions are ready to harvest when the tops fall over and start turning yellow. Leave them in the ground for an additional 2–3 weeks to cure before pulling them completely. This ensures they have a longer storage potential.
Can I plant multiple onion varieties together?
Yes, you can plant multiple onion varieties together as long as they share similar growing preferences. Be cautious of spacing them adequately to prevent competition for nutrients, and always be aware of their day-length requirements.