Rosemary in Zone 6B — Pacific Northwest

Rosemary is a fantastic addition to any Pacific Northwest garden. Its distinct flavor elevates roasted vegetables and grilled meats, and the fragrant foliage is a joy to brush against. Plus, it's a perennial, so you'll have fresh rosemary year after year, and its evergreen foliage adds winter interest.

While our mild summers and wet springs present some challenges, Rosemary is surprisingly well-suited to our climate. Our 162-day growing season gives it plenty of time to mature. With a little attention to timing and well-draining soil, you can enjoy a thriving rosemary plant.

Starting rosemary from seed indoors is possible, but it's not the easiest route. Rosemary germination can be erratic, and the seedlings grow slowly. If you're up for a challenge, or want a specific variety not available locally, give it a try!

Start your seeds indoors from mid February through early March, about 12 weeks before you plan to transplant. Use seed trays with a good seed-starting mix, provide consistent bottom watering to avoid damping off, and ensure they have plenty of light (a grow light is ideal, given our overcast spring days). Keep the soil warm, around 70-75°F, to encourage germination.

Honestly, for most PNW gardeners, buying an established Rosemary plant from a local nursery is the way to go. It'll save you time and frustration and give you a head start on enjoying fresh rosemary.

Transplant your rosemary outdoors from mid May through early June, after the last expected frost. 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-draining soil. Rosemary needs at least 6-8 hours of sun each day. Space your plants 24-36 inches apart to allow for good air circulation. Keep an eye on the weather forecast, as late frosts can still occur in early May.

Given our cool soil in spring, consider amending your soil with compost or planting in raised beds to improve drainage and warm the soil faster. Remember, rosemary hates wet feet!

Rosemary is drought-tolerant once established, which is a huge plus during our dry summer months. Overwatering is a much bigger threat than underwatering in the Pacific Northwest, especially with our wet springs.

During the first year, water regularly to help your rosemary establish a strong root system. After that, let the soil dry out almost completely between waterings. Stick your finger about 2 inches deep into the soil – if it's still moist, hold off on watering. You'll likely only need to water established rosemary about once a week, or even less, during our mild summer months.

Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases. A layer of gravel mulch around the base of the plant can help improve drainage and prevent soil from splashing onto the leaves. If the leaves turn yellow and start to drop, you're likely overwatering. If the leaves look wilted and dry, it's time to water.

Rosemary requires minimal pruning, which is great for low-maintenance gardens. The main goal is to maintain its shape and remove any dead or damaged branches.

Prune lightly after flowering, which usually occurs in spring or early summer. Avoid cutting into old wood, as it may not regrow. Shape your rosemary plant in spring, removing any unruly growth to encourage a bushier habit.

As the first frost approaches in early October, you can give your rosemary a light trim to tidy it up for winter. Avoid heavy pruning in the fall, as this can stress the plant before the cold weather arrives.

You can start harvesting rosemary from mid August through late September, once the plant is well-established. Rosemary is ready to harvest when the stems are at least 4-6 inches long.

To harvest, simply snip off the stem tips with clean shears or scissors. Avoid taking more than 1/3 of the plant at any one time, as this can weaken it. The younger, more tender stem tips have the best flavor. Woody stems are generally too tough to eat.

Continue harvesting throughout the growing season to encourage new growth. As the first frost approaches in early October, harvest any remaining rosemary you want to dry or freeze for winter use. You can also bring potted rosemary indoors to overwinter in a sunny location.

Here are some common problems you might encounter with Rosemary in the Pacific Northwest:

Root Rot from Overwatering

• What it looks like: Yellowing leaves, wilting even when the soil is moist, and eventually, the plant may die. The roots will be brown and mushy instead of white and firm.
• What causes it: Overwatering and poor drainage. Rosemary prefers dry conditions, and our wet springs can easily lead to root rot if the soil doesn't drain well.
• How to fix/prevent it: Plant rosemary in well-draining soil or raised beds. Avoid overwatering, especially during wet periods. Make sure your pot has drainage holes. Use the finger test to check soil moisture before watering.

Powdery Mildew

• What it looks like: A white or grayish powdery coating on the 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, which can happen even in our generally dry-summer climate if you have dense plantings.
• How to fix/prevent it: Improve air circulation by spacing plants properly and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays can help. Milk spray (1 part milk to 9 parts water) is also 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 can explode during drought stress, even in our mild summers.
• 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 late blight isn't a direct threat to rosemary, the conditions that favor it (wet, humid weather) can also create problems for rosemary by promoting fungal diseases. Our cool soil in spring can slow growth, making rosemary more susceptible to problems. The dry-summer humidity can sometimes be deceptive, as even a little humidity can be enough to trigger powdery mildew.

Rosemary thrives alongside other Mediterranean herbs in the Pacific Northwest garden. Sage, thyme, and lavender make excellent companions, as they share similar growing requirements (full sun, well-draining soil, low water). Plant rosemary near green beans and carrots, as it is believed to repel certain pests that can damage these crops.

Avoid planting rosemary near mint. Mint is very aggressive and can quickly take over a garden bed, crowding out other plants. Also, mint prefers moist soil, which is the opposite of what rosemary needs.