Yarrow in Zone 7A — Northeast

Yarrow is a fantastic addition to any Northeast garden. Its delicate, feathery foliage and clusters of colorful flowers add beauty, and it's a magnet for beneficial insects. Plus, the cool nights we often get in the Northeast seem to intensify the fragrance of the flowers, making it even more enjoyable.

Our short growing season and occasional late spring frosts can be a concern, but yarrow is quite hardy. With a little planning and early starts, you can easily make the most of our 198-day growing season and enjoy yarrow's blooms for months.

Starting yarrow indoors isn't strictly necessary, but it can give you a head start, especially if you want flowers in the first year. If you're itching to get growing during those long winter months, sow seeds indoors from late January through mid February, about 8 weeks before you plan to transplant.

Use seed trays with a good seed-starting mix. Keep the soil consistently moist (bottom watering works great to prevent damping off) and provide a warm location with plenty of light. A simple grow light will do the trick, as our late spring can mean less natural light early on.

Transplant your yarrow seedlings outdoors from late March through late April, once the danger of a hard freeze 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 cooler temperatures and stronger sunlight we often experience in early spring.

Space the plants 12-18 inches apart in a sunny spot. While late frosts are always a possibility in the Northeast, yarrow is quite tolerant. If you're particularly worried, cover the young plants with a frost blanket on cold nights. Buying starts ensures flowers the first year.

Direct sowing yarrow is a simple and effective method, especially if you're not looking for blooms in the first season. Sow seeds directly into the garden from early April through early August. This wide window gives you flexibility to work around our often unpredictable spring weather.

Choose a location with full sun and well-drained soil. Yarrow isn't picky, and it even thrives in our rocky New England soil. Simply scatter the seeds on the surface, lightly press them in, and keep the soil moist until they germinate. Thin seedlings to 12-18 inches apart.

Yarrow is incredibly drought-tolerant once established, which is a huge plus for busy Northeast gardeners. However, it's essential to provide adequate moisture during the initial establishment period.

In the spring, water regularly until the plants are well-rooted. After that, let the soil dry out between waterings. Stick your finger about 2 inches deep into the soil – if it's dry, it's time to water. During the moderate heat and moderate-to-humid summers here, you likely won't need to water more than once a week, giving the plants about an inch of water.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our humid climate. Signs of underwatering include wilting leaves and stunted growth. Overwatering, on the other hand, can lead to floppy growth and root rot. A light layer of mulch, like shredded bark, can help retain moisture and suppress weeds, but don't overdo it – yarrow prefers well-drained conditions.

Pruning yarrow is simple and keeps it looking its best. Deadhead spent flowers throughout the growing season to encourage a second flush of blooms. Simply snip off the flower heads just below the lowest set of petals.

In the fall, after the first frost around late October, cut the plants back to their basal foliage. This tidies up the garden and prepares the plants for winter dormancy. Yarrow can be aggressive, so divide the clumps every 2-3 years to prevent overcrowding.

You can expect your first yarrow harvest starting in mid June and continuing through early November. The flowers are ready to harvest for drying when they are fully open and the colors are vibrant.

To harvest, simply cut the stems at the base of the plant, leaving enough foliage for continued growth. Hang the stems upside down in a cool, dark, and dry place to dry. Regular harvesting encourages more blooms throughout our short growing season.

As the first frost approaches in late October, you can still harvest any remaining flowers. They may not be as perfect as the summer blooms, but they'll still add a touch of color and fragrance to your dried arrangements.

Here are three common problems you might encounter with yarrow in the Northeast:

Aggressive Spreading

• What it looks like: Yarrow spreads via rhizomes, and you might find it popping up in unwanted areas of your garden.
• What causes it: Yarrow thrives in our climate and can quickly fill in available space, especially in well-drained soil.
• How to fix/prevent it: Plant yarrow in a contained area, like a raised bed or surrounded by edging. Divide the plants every 2-3 years to keep them in check. Regularly remove any unwanted shoots that pop up.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems. Leaves curl, yellow, and die.
• What causes it: Powdery mildew thrives in our warm days, cool nights, and moderate humidity.
• How to fix/prevent it: Improve air circulation by spacing plants adequately and pruning. Remove affected leaves promptly. Neem oil or potassium bicarbonate sprays can help. A milk spray (1 part milk to 9 parts water) is also 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: Aphids reproduce rapidly and thrive in warm weather.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage ladybugs and lacewings. Insecticidal soap works for heavy infestations.

Northeast Specific Challenges: Our moderate heat, moderate-to-humid humidity, and even rainfall can create ideal conditions for powdery mildew. Be vigilant about air circulation and avoid overhead watering to minimize this risk.

Yarrow is a great companion plant for many vegetables and herbs in the Northeast garden. It attracts beneficial insects like ladybugs and lacewings, which prey on pests that can damage your tomatoes and peppers. Planting yarrow near these vegetables can help reduce pest pressure.

Yarrow also benefits herbs like rosemary and thyme by improving their growth and flavor. It's a good companion for strawberries, as it attracts pollinators and can help deter certain pests. Avoid planting yarrow near brassicas like cabbage and broccoli, as it can attract cabbage moths.