Yarrow in Zone 7A — Pacific Northwest

Yarrow is a fantastic addition to any Pacific Northwest garden. Its feathery foliage and clusters of colorful flowers not only add beauty but also attract beneficial insects, making it a valuable companion plant. Plus, the cool nights here seem to intensify the colors and fragrance, and it makes a great dried flower.

Our mild summers and wet springs can present some unique challenges, but Yarrow is well-suited to our climate. With a 183-day growing season, you have ample time to establish this hardy perennial and enjoy its benefits. Careful timing is key to success.

Starting Yarrow indoors isn't essential, as it direct sows easily, but it can give you a jump start, especially if you want flowers the first year. Begin in early to late February, about eight weeks before the typical transplant window. Use seed trays with a good seed-starting mix, and provide warmth (a heat mat helps) and plenty of light, especially given our overcast spring days.

Be sure to water from the bottom to avoid damping off. Set the tray in a shallow pan of water and let the soil soak it up. This encourages strong root growth and prevents the soil surface from staying too damp, which can be a problem in our wet springs.

Transplant your Yarrow seedlings outdoors in early April through early May, once the danger of hard frost has passed. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. Place them in a sheltered spot, increasing the amount of sunlight and wind exposure each day.

Space your Yarrow plants 12-18 inches apart to allow for their clumping growth habit. Be mindful of late-season cold snaps when transplanting. If a frost threatens, cover your young plants with row covers or blankets. Remember that Yarrow is a perennial, so investing in starts can get you flowering plants the first year.

Direct sowing Yarrow is a simple and effective method, especially if you're patient. Sow seeds mid-April through early August, after the soil has warmed up a bit. Yarrow isn't too picky about soil, but it does prefer well-drained conditions.

Lightly rake the seeds into the soil surface and keep them consistently moist until germination. Thin seedlings to 12-18 inches apart as they grow. Direct sowing is convenient, but you might not get flowers until the second year.

Yarrow is incredibly drought-tolerant once established, making it a perfect fit for our dry summer months in the Pacific Northwest. During the wet springs, you likely won't need to water at all unless you're experiencing an unusually dry spell. Let nature do its thing!

During our mild summer heat, check the soil moisture using the finger test. Stick your finger about two inches deep into the soil near the base of the plant. If it feels dry, it's time to water. Aim for about an inch of water per week during dry periods, but err on the side of less rather than more.

Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases, especially if we have a spell of unusually humid weather. Mulching around your Yarrow plants with gravel or bark chips can help retain soil moisture and suppress weeds, which reduces the need for watering.

Signs of underwatering include wilting leaves and stunted growth, while overwatering can lead to floppy, weak stems and potentially root rot. Remember, Yarrow prefers well-drained soil, so avoid planting it in areas that tend to stay soggy.

Pruning Yarrow is straightforward and helps to encourage continued blooming and maintain a tidy appearance. Deadhead spent flowers regularly throughout the growing season to promote a second flush of blooms. Simply snip off the flower heads just below the point where they connect to the stem.

In the fall, after the first frost around mid-October, cut the plant back to its basal foliage (the leaves at the base of the plant). This helps to tidy up the garden for winter and allows new growth to emerge in the spring. Yarrow can be aggressive, so divide it every 2-3 years to keep it in check.

In the Pacific Northwest, you can expect your first Yarrow harvest from late June through late October. The flowers are ready to harvest when they are fully open and displaying their vibrant colors. Harvesting flowers encourages more to form, so it's a win-win.

To harvest, simply cut the stems just above a leaf node using sharp scissors or pruners. For drying, hang the flower stems upside down in a cool, dark, and dry place until they are completely dry. Yarrow is an excellent dried flower, retaining its color and fragrance for months.

Yarrow doesn't ripen off the vine, so it's best to harvest when the flowers are at their peak. Even as the first frost approaches in mid-October, you can continue to harvest any remaining flowers. The mild fall we often experience allows for an extended harvest period.

Yarrow is generally a low-maintenance plant, but here are a few common problems to watch out for in the Pacific Northwest:

Spreading Aggressively

• What it looks like: Yarrow can spread quickly via rhizomes (underground stems), popping up in unwanted areas of your garden.
• What causes it: Its vigorous growth habit and adaptability to various soil conditions contribute to its spreading nature.
• How to fix/prevent it: Plant Yarrow in a contained area or use edging to prevent it from spreading. Regularly divide the plant every 2-3 years to control its size. Remove unwanted shoots as they appear.

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: While Yarrow is relatively problem-free, our dry summer months can sometimes exacerbate powdery mildew issues if plants are crowded and air circulation is poor. Ensure good spacing and consider a preventative milk spray if you've had problems in the past. Late blight isn't a direct concern for Yarrow, but maintaining good garden hygiene helps prevent its spread to other susceptible plants.

Yarrow is a great companion plant for several reasons. It attracts beneficial insects like ladybugs and hoverflies, which prey on pests that can harm other plants.

Good companions for Yarrow include:

• Tomatoes and Peppers: Yarrow attracts beneficial insects that help pollinate and protect these crops from pests.
• Herbs: Yarrow enhances the essential oil production of many herbs, making them more fragrant and flavorful.
• Strawberries: Yarrow can help repel pests that attack strawberries.

Avoid planting Yarrow near plants that prefer very rich, moist soil, as Yarrow thrives in drier, less fertile conditions.