Yarrow in Zone 6B — Northeast

Yarrow is a fantastic addition to any Northeast garden. Its delicate, feathery foliage and clusters of colorful flowers bring beauty and attract beneficial insects. Plus, the cool nights we often get here in the Northeast seem to deepen the colors and fragrance, making it even more rewarding to grow.

Our short growing season and occasional late frosts can be a challenge, but Yarrow is quite hardy. If you plan accordingly and take advantage of our 183-day growing season, you can easily enjoy a bountiful harvest of blooms.

Starting Yarrow indoors in the Northeast is possible, but not always necessary. If you're aiming for earlier blooms, or want a head start on our short growing season, it can be helpful. Start seeds indoors from late January through mid February, about 8 weeks before you plan to transplant them outside.

Use seed trays with a good seed-starting mix. Keep them warm (around 70°F) and provide plenty of light – a grow light works wonders, especially with our late-arriving spring sunshine. Remember to water from the bottom to avoid damping off. This is especially helpful considering our often-damp spring weather.

Transplant your Yarrow seedlings outdoors in early to late April, once the danger of a hard frost has passed. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and stronger sunlight.

Space the plants 12-18 inches apart to allow for their clumping growth habit. Keep in mind that Yarrow is a perennial, so buying starts might give you flowers in the first year. Be prepared for some chilly nights still – a frost blanket can be helpful if a late cold snap threatens.

Direct sowing Yarrow is a perfectly viable option in the Northeast, especially if you're not in a rush for early blooms. Sow seeds directly into the garden from mid April through late July. This wide window allows for flexibility, especially since our springs can be unpredictable.

Prepare the soil by loosening it and removing any rocks – we all know about our rocky New England soil! Yarrow prefers well-drained soil, so avoid heavy clay. Keep the soil consistently moist until the seedlings emerge. Space the seeds 12-18 inches apart, and thin the seedlings as needed.

Yarrow is incredibly drought-tolerant once established, making it a great choice for the Northeast garden. However, young plants do need regular watering to get them going. The key is to avoid overwatering, which can lead to floppy growth and other problems.

During the first few weeks after planting, water deeply once or twice a week, providing about 1 inch of water. Use the "finger test" – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. After the initial establishment period, you can reduce watering significantly. Established Yarrow can usually get by with rainfall alone, given our even rainfall pattern in the Northeast.

Water at the base of the plants to avoid wetting the foliage, since our moderate-to-humid summers can increase the risk of fungal diseases. Signs of underwatering include wilting leaves and stunted growth. Overwatering, on the other hand, can cause yellowing leaves and root rot. A light layer of mulch around the base of the plants can help retain moisture and suppress weeds, especially during our sometimes-dry spells in midsummer.

Pruning Yarrow is simple and helps to encourage continued blooming. The main task is deadheading, which means removing spent flowers. Do this regularly throughout the growing season, from mid June through late October.

Simply snip off the flower heads just below the lowest set of leaves. This will encourage the plant to produce more flowers, giving you a longer bloom period. Toward the end of the season, after the first frost around mid- October, cut the plant back to its basal foliage. This helps keep the plant tidy over the winter. Since Yarrow can be aggressive, divide the clumps every 2-3 years to prevent overcrowding.

You can expect your first Yarrow harvest around mid June, about 65 days after planting. The flowers are ready to harvest when they are fully open and displaying their vibrant colors. The harvest window extends through late October, so you can enjoy fresh or dried blooms for much of our growing season.

To harvest, simply cut the stems at the base of the flower head. For drying, hang the stems upside down in a cool, dark, and dry place. Regular harvesting encourages the plant to produce more flowers, so keep at it! As our first frost approaches around mid- October, harvest any remaining flowers to dry and enjoy indoors.

Here are a few common problems to watch out for with Yarrow in the Northeast:

Aggressive Spreading

• What it looks like: Yarrow can spread beyond its intended area, popping up in unwanted places in your garden.
• What causes it: Yarrow spreads through rhizomes (underground stems), and it's quite vigorous. Our even rainfall and moderate temperatures can encourage its growth.
• How to fix/prevent it: Plant Yarrow in a contained area or use edging to prevent it from spreading. Divide the plant every 2-3 years to keep it in check. Remove unwanted shoots as soon as you see them.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems. Leaves curl, yellow, and die.
• What causes it: Various fungi thrive in warm days, cool nights, and moderate humidity. Dry leaf surfaces actually favor it.
• 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.

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).

Northeast Specific Challenges: Our moderate heat, moderate-to-humid humidity, and even rainfall can create ideal conditions for both powdery mildew and aphid infestations. Regular monitoring and preventative measures are key to keeping your Yarrow healthy in our Northeast climate.

Yarrow makes a great companion plant for many vegetables and herbs in the Northeast garden. It attracts beneficial insects like ladybugs and lacewings, which help control pests.

• Tomatoes and Peppers: Yarrow attracts beneficial insects that prey on tomato hornworms and aphids, common pests in our Northeast gardens.
• Herbs: Planting Yarrow near herbs like rosemary and thyme can enhance their flavor and growth.
• Strawberries: Yarrow can help deter pests that attack strawberries.

Avoid planting Yarrow near plants in the Brassica family (cabbage, broccoli, kale) as it can attract cabbage moths.