Yarrow in Zone 7B — Pacific Northwest

Yarrow is a fantastic addition to any Pacific Northwest garden. Its feathery foliage and clusters of blooms add beauty, and it attracts beneficial insects like crazy. Plus, its drought tolerance means you won't be chained to the hose during our dry summer months.

While our wet springs and mild summers can present unique challenges, Yarrow is well-suited to our 193-day growing season. With a little attention to timing, you'll have no problem enjoying its beauty and benefits.

Starting Yarrow indoors isn't strictly necessary, but it can give you a head start, especially if you want blooms the first year. Sow seeds indoors from late January through mid February, about eight weeks before you plan to transplant. Use seed trays with a good seed-starting mix and provide bottom watering to keep the soil consistently moist without soaking the delicate seedlings.

Keep the trays in a warm spot with plenty of light – a sunny windowsill or under grow lights works well. Remember, our overcast spring days can be deceiving; supplemental light is often beneficial.

Transplant your Yarrow seedlings outdoors in early to late April, once the soil has warmed up a bit. Be sure to harden them off for about a week beforehand by gradually exposing them to outdoor conditions. This prevents shock from our sometimes unpredictable spring weather.

Space your plants 12-18 inches apart in a sunny spot with well-drained soil. Yarrow is a perennial, so if you want flowers in the first year, buying starts from your local nursery is a good option.

Direct sowing Yarrow is a simple and effective method, especially if you're not in a rush for first-year blooms. Sow seeds from mid April through early August, once the soil has warmed up and the risk of frost has passed. Prepare the soil by loosening it and removing any weeds.

Sprinkle the seeds lightly over the surface and gently press them into the soil. Keep the soil consistently moist until the seedlings emerge. Thin the seedlings to 12-18 inches apart as they grow.

Yarrow thrives on neglect, making it perfect for our dry summer months in the PNW. Once established, it's very drought-tolerant. The key is to avoid overwatering, which can lead to floppy growth and other problems.

During our wet springs, you likely won't need to water at all unless we have an unseasonably dry spell. Once summer arrives, check the soil moisture with the finger test – if the top two inches are dry, it's time to water. Aim for about an inch of water per week, watering at the base of the plant to avoid wetting the foliage.

In our dry-summer climate, overhead watering isn't usually a problem, but if you notice signs of powdery mildew, switch to watering at the base. Yellowing leaves can indicate overwatering, while wilting signals underwatering. A light layer of gravel mulch around the base of the plant can improve drainage and reduce moisture retention.

Regular deadheading is essential for keeping your Yarrow looking its best and encouraging a second flush of blooms. Throughout the growing season, remove spent flowers by cutting the stem back to a healthy leaf node. This prevents the plant from putting energy into seed production and encourages more flowers.

In late fall, after the first frost around late October, cut the plant back to its basal foliage. Yarrow can be aggressive, so divide the clumps every 2-3 years to keep it in check.

You can expect your first harvest of Yarrow blooms starting in mid June and continuing through early November. Harvest the flowers for drying when they are fully open and the color is vibrant. Cut the stems close to the base of the plant, leaving plenty of foliage for continued growth.

Hang the stems upside down in a cool, dry place to dry. Regular harvesting encourages continued production throughout the season. Even as our first frost approaches in late October, you can often still harvest a few blooms, extending the season a bit longer.

Here are the top 3 problems to watch out for with Yarrow in the Pacific Northwest:

Spreading Aggressively

• What it looks like: Yarrow quickly expands beyond its designated area, crowding out other plants.
• What causes it: Yarrow spreads through rhizomes (underground stems) and seeds, and it's very good at it. Our mild climate allows it to thrive.
• How to fix/prevent it: Plant Yarrow in a contained area or use edging to prevent spread. Divide the plant every 2-3 years to control its size. Remove seed heads before they mature to prevent self-seeding.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems, and sometimes fruit. Leaves curl, yellow, and die. Reduces plant vigor.
• What causes it: Various fungi that thrive in warm days, cool nights, and moderate humidity. Dry leaf surfaces actually favor it (unlike most fungi).
• How to fix/prevent it: Improve air circulation through spacing and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays help. Milk spray (1 part milk to 9 parts water) is surprisingly effective. Plant resistant varieties.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects. Populations explode in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Strong water spray knocks them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer (it attracts them).

Pacific Northwest Specific Challenges: Our mild summers and dry-summer rainfall pattern actually benefit Yarrow. Late blight is less of a concern for Yarrow than for tomatoes. The key is to provide well-drained soil to prevent root rot, which can be exacerbated by our wet springs.

Yarrow is a great companion plant for many vegetables and herbs in the Pacific Northwest garden. It attracts beneficial insects like ladybugs and hoverflies, which prey on aphids and other pests.

Good companions include tomatoes and peppers, as Yarrow helps to repel pests that can damage these crops. Herbs like rosemary and thyme also benefit from Yarrow's pest-repelling properties. Strawberries benefit from the increased pollination provided by the beneficial insects that Yarrow attracts. Avoid planting Yarrow near plants that prefer very rich soil, as Yarrow thrives in poor soil.