Rosemary in Zone 7B — Pacific Northwest

Rosemary is a fantastic addition to any Pacific Northwest garden. Its distinctive flavor elevates roasted vegetables, grilled meats, and even simple breads, all while thriving in our mild summers and cool nights. Plus, the fragrant foliage is a welcome bonus, attracting pollinators and adding beauty to your herb garden.

While the PNW isn't exactly known for its Mediterranean climate, Rosemary can flourish here with a little attention to timing. Our 193-day growing season gives you plenty of time to establish it, especially if you give it a head start. The key is to work *with* our climate.

Starting Rosemary from seed indoors in the PNW is possible, but it can be a bit of a patience game. Rosemary germination can be erratic, and the seedlings grow slowly, especially with our overcast spring days. Still, if you're feeling ambitious, starting seeds indoors from late January through mid February gives you a head start.

Use seed trays with a good seed-starting mix and provide consistent bottom watering to avoid damping off. Place the trays on a heat mat to encourage germination, and provide plenty of light with grow lights, since natural light is often limited in the PNW during this time. Be prepared for slow growth and consider buying established plants if you want a quicker harvest.

Transplant your Rosemary outdoors from late April through mid May, after the risk of hard frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Space plants 24-36 inches apart in a sunny spot with well-drained soil. Keep an eye on the weather forecast – a late cold snap can still happen, even in late spring. Rosemary is slow to get going, so be patient. Honestly, for most PNW gardeners, buying established Rosemary plants is the easiest and most reliable way to go.

Rosemary is very drought-tolerant once established, making it a great choice for the dry summer months we experience in the Pacific Northwest. Overwatering is a far bigger threat than underwatering. In fact, it's the most common reason Rosemary plants fail here.

During our wet springs, you likely won't need to water at all, unless the plant is in a very well-draining container. Once the dry summer arrives, check the soil moisture before watering. Use the finger test: stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week during the driest periods, but only if the soil is actually dry. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our sometimes humid conditions.

Signs of underwatering include wilting or drooping leaves. Overwatering can cause yellowing leaves and potentially root rot. A light layer of mulch, like pea gravel, can help conserve moisture and improve drainage, which is especially helpful for Rosemary in our climate.

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

Shape your Rosemary in the spring as new growth emerges. You can trim it back to encourage bushier growth and remove any dead or damaged branches. In late October, as the first frost approaches, you can give it a final light trim, but avoid heavy pruning at this time of year.

You can begin harvesting Rosemary from late July through early September, about 90 days after transplanting. Look for healthy, 4-6 inch stem tips. These are the most flavorful and tender parts of the plant.

Harvest by snipping off the stem tips with clean pruning shears. Never take more than 1/3 of the plant at a time, as this can weaken it. Avoid harvesting the woody stems, as they tend to be too tough to eat. Rosemary is a continuous harvest plant, so you can harvest throughout the growing season.

As the first frost approaches in late October, harvest any remaining stems that you want to use. You can dry them for later use. Even with a light frost, the flavor degrades.

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

Root Rot from Overwatering

• What it looks like: Yellowing leaves, wilting, and stunted growth. The roots will appear brown and mushy.
• What causes it: Overwatering and poor drainage. Our wet springs and tendency to overcompensate during the dry summer months can create ideal conditions for root rot.
• How to fix/prevent it: Ensure your Rosemary is planted in well-draining soil. Water only when the top 2 inches of soil are dry. Improve drainage by adding gravel to the planting hole or growing in raised beds or containers.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves may curl, yellow, and eventually die.
• What causes it: Fungi that thrive in warm days, cool nights, and moderate humidity. Dry leaf surfaces actually favor it (unlike most fungi). The PNW's summer conditions can be conducive to powdery mildew.
• How to fix/prevent it: Improve air circulation by spacing plants properly and pruning dense growth. Remove affected leaves. Neem oil or potassium bicarbonate sprays can help. 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 during periods of drought stress, which can occur during our dry summer months.
• How to fix/prevent it: 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: Late blight isn't generally a problem for Rosemary itself, but the conditions that favor blight (dampness) can create other fungal issues. The dry-summer humidity and dry-summer rainfall pattern means you need to be vigilant about proper watering and airflow to prevent root rot and powdery mildew. Our mild heat generally isn't a problem for Rosemary, which prefers full sun, but be sure to provide adequate water during extended dry periods to prevent spider mites.

Rosemary benefits from companion planting. Sage, thyme, and lavender all thrive in similar dry, sunny conditions, creating a harmonious and low-maintenance herb garden. Green beans are good companions because they help fix nitrogen in the soil, which can benefit Rosemary's growth. Carrots also make good companions, as their presence in the soil can deter some pests that might bother Rosemary.

Avoid planting Rosemary near mint. Mint is incredibly invasive and can quickly take over your garden, competing with Rosemary for resources. Mint also prefers moist conditions, which are the opposite of what Rosemary needs to thrive.