When to Plant Rosemary in Washington (2026 Guide)
Growing rosemary in Washington can be highly rewarding, provided you understand the local climate dynamics. Depending on your specific location, your planting strategy will hinge on the average frost dates. For example, those in Zone 6b will enjoy a relatively early last frost date of April 9, while gardeners in Zone 5b must wait until May 6 before the danger of frost passes.
Washington's climate can present unique challenges for rosemary cultivation. Areas like Spokane may have unpredictable late frosts, while regions near the coast may experience humidity that affects the plant's growth. Regardless, rosemary is an adaptable herb that thrives in full sun and well-drained soil, making it a great choice for savvy gardeners across the state.
To ensure a successful harvest, understanding the best planting and harvest windows is crucial. In many of Washington's temperate regions, you can expect a growing season of at least 150 days. With the right strategies, you can have a bounty of fresh rosemary to enhance your culinary creations from mid-summer into fall.
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 9 | Transplant outdoors after April 9, post last frost | Direct sow outdoors after April 9 | Harvest from July 1 – September 30 |
| Zone 6a | Start February 15 – March 1, ~6–8 weeks before April 20 | Transplant outdoors after April 20, post last frost | Direct sow outdoors after April 20 | Harvest from July 1 – September 30 |
| Zone 5b | Start March 1 – March 15, ~6–8 weeks before May 6 | Transplant outdoors after May 6, post last frost | Direct sow outdoors after May 6 | Harvest from July 15 – September 30 |
Rosemary Planting Windows in Washington
- Indoor start: Start rosemary seeds indoors from February 15 to March 15, depending on your zone.
- Transplant outdoors: Transplant rosemary outdoors once the last frost has passed, which varies from April 9 to May 6 depending on your zone.
- Harvest: You can begin harvesting rosemary from July 1 and continue until the end of September, ensuring the best flavor.
Common Mistakes Growing Rosemary in Washington
- One common mistake in Washington is planting rosemary too early. The late frosts, especially in April for Zone 6b or May for Zone 5b, can severely damage young plants. Always adhere to the last frost dates based on your specific zone.
- Overwatering is another frequent error amongst novice gardeners in Washington. Rosemary thrives in well-drained soil and can suffer from root rot when subjected to excess moisture, particularly when planted in heavy clay soils common across the state.
- Many gardeners underestimate the need for full sun. In Washington, areas that are shaded by trees or structures can impede rosemary growth, resulting in leggy plants that do not thrive. Aim for at least six hours of direct sunlight each day.
- Ignoring humidity levels in certain Washington regions can also be detrimental. Coastal areas may experience higher humidity, which can lead to fungal issues, especially if rosemary is kept too wet or not pruned adequately.
- Lastly, not protecting rosemary from winter temperatures below 10°F can be disastrous. Particularly for those in areas with colder winters, it's crucial to take measures such as bringing container plants indoors or providing adequate winter protection.
Frequently Asked Questions
What if I'm in a cold pocket of Washington?
If you're in a colder microclimate, consider starting your rosemary indoors earlier. Use heat mats to encourage soil warmth and aim to transplant outside once all frost threats have passed beyond May 6.
Can I still plant rosemary in May?
Yes, you can plant rosemary in May, but be aware that waiting until after May 6 is crucial in areas with colder zones. Always confirm that there is no risk of frost before transplanting.
What type of soil is best for rosemary?
Rosemary prefers sandy, well-drained soil types. If your Washington soil is heavy clay, amend it with sand or plant it in raised beds to improve drainage and avoid root rot.
Is it too late to start rosemary now?
If you're contemplating starting rosemary after May 6, it's not too late, but choose to use container plants that can be brought indoors during any unexpected late frosts. This gives you flexibility and protection if needed.
How do I know when to harvest rosemary?
You should harvest rosemary when it develops strong scents and numerous new growths, typically from July 1 through September 30. Regular harvesting encourages bushy growth and prevents legginess.