Rosemary in Zone 7A — Pacific Northwest

Rosemary is a fantastic addition to any Pacific Northwest garden. Its distinctive aroma and flavor elevate everything from roasted vegetables to grilled meats, and it's a beautiful, evergreen shrub that adds year-round interest to your garden. Plus, the cool nights we often have here in the summer seem to intensify its flavor, making it even more rewarding to grow.

While our wet springs and mild summers can present some challenges, growing rosemary in Zone 7A is definitely achievable. With a bit of planning and attention to its specific needs, you can enjoy fresh rosemary from your garden for many months of our 183-day growing season.

Starting rosemary from seed indoors is possible, but it's honestly a slow and somewhat frustrating process. Rosemary germination can be erratic, and the seedlings grow very slowly. If you're up for a challenge, go for it, but most PNW gardeners find it easier to buy established plants.

If you decide to start from seed, sow indoors in early to late February, about 12 weeks before you intend to transplant. Use seed trays with good drainage and provide consistent warmth (around 70-75°F) and bright light. Bottom watering helps prevent damping-off, which can be a problem with slow-growing seedlings, especially with our overcast spring days.

Transplant your rosemary outdoors in early to late May, once the danger of frost has passed and the soil has warmed up a bit. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Choose a sunny spot with well-drained soil and space plants 24-36 inches apart. Keep an eye on the weather forecast, as we can still get cool snaps and late frosts even in May. If frost is predicted, cover your young plants to protect them. Rosemary is very slow and difficult from seed, so consider buying established plants from a local nursery.

Rosemary thrives on neglect, especially here in the Pacific Northwest. Once established, it's very drought-tolerant and prefers dry conditions. Overwatering and poor drainage are the main reasons rosemary plants fail in our region.

During our wet springs, you likely won't need to water rosemary at all, unless we have an unusually dry spell. In the dry summer months, water deeply but infrequently, allowing the soil to dry out completely between waterings. Use the "finger test" – if the top 2 inches of soil are dry, it's time to water. Aim for about 1 inch of water per week during the hottest part of the summer, but only if we aren't getting regular rainfall. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our dry-summer humidity.

Signs of underwatering include wilting or drooping leaves. Overwatering can cause yellowing leaves, root rot, and a generally unhappy plant. A light layer of gravel mulch around the base of the plant can help improve drainage and prevent soil from splashing onto the foliage.

Rosemary requires minimal pruning. The best approach is to prune lightly after flowering to maintain its shape and encourage bushier growth. Avoid cutting into old wood, as it may not regrow.

Shape your rosemary plant in the spring, removing any dead or damaged branches. As the first frost approaches in mid- October, you can give it a light trim to tidy it up, but avoid heavy pruning at this time of year. Focus on harvesting stems for cooking or drying.

You can expect your first harvest of rosemary in early August through mid September, about 90 days after transplanting. Look for 4-6 inch stem tips that are green and pliable. These are the most flavorful and tender parts of the plant.

To harvest, simply snip off the stem tips with clean pruners. Never take more than 1/3 of the plant at any one time, as this can weaken it. Avoid harvesting woody stems, as they can be tough and less flavorful. Regular harvesting encourages continued production throughout the season.

As the first frost approaches in mid- October, harvest any remaining rosemary stems that you want to use for cooking or drying. You can dry rosemary by hanging the stems upside down in a cool, dark place, or by using a dehydrator.

Here are the top 3 problems you might encounter growing rosemary in the Pacific Northwest:

Root Rot from Overwatering

• What it looks like: Yellowing leaves, wilting, and a general decline in plant health. The roots may be brown and mushy.
• What causes it: Overwatering, especially in heavy clay soils with poor drainage. Our wet springs can exacerbate this issue.
• How to fix/prevent it: Plant rosemary in well-drained soil. Water deeply but infrequently, allowing the soil to dry out between waterings. Improve drainage by amending the soil with compost or gravel. Consider growing rosemary in a raised bed or container.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves may curl, yellow, and die.
• What causes it: Various fungi that thrive in warm days, cool nights, and moderate humidity. Dry leaf surfaces actually favor it.
• How to fix/prevent it: Improve air circulation by spacing plants properly and pruning to open up the plant. Remove affected leaves. Neem oil or potassium bicarbonate sprays can help. A milk spray (1 part milk to 9 parts water) is surprisingly effective.

Spider Mites

• What it looks like: Fine stippling on leaves (tiny white dots). Fine webbing on leaf undersides and between stems. Leaves turn bronze or yellow.
• What causes it: Tiny arachnids that thrive in hot, dry conditions. Populations explode in drought stress.
• How to fix/prevent it: A strong water spray (daily for a week) is the best treatment. Increase humidity around plants. Neem oil or insecticidal soap can also be used.

Pacific Northwest Specific Challenges: While rosemary generally prefers drier conditions, our cool, wet springs and mild, dry summers can create a tricky balance. Be especially vigilant about avoiding overwatering during the spring. Our dry-summer rainfall helps reduce the risk of fungal diseases, but powdery mildew can still be a problem if air circulation is poor.

Rosemary benefits from being planted near certain companions in the Pacific Northwest garden. Sage, thyme, and lavender are all excellent companions because they share similar growing requirements (full sun, well-drained soil, low water) and attract beneficial insects. Green beans are helpful because they fix nitrogen in the soil, which can benefit rosemary, and carrots are said to deter rosemary beetle.

Avoid planting rosemary near mint. Mint is invasive and can quickly take over, crowding out rosemary and competing for resources. Mint also prefers moist soil, which is the opposite of what rosemary needs.