Yarrow in Zone 6A — Northeast

Yarrow is a fantastic addition to any Northeast garden. Its feathery foliage and clusters of blooms provide beauty, attract beneficial insects, and are excellent for drying. Plus, the cool nights we often get here in the summer seem to deepen the flower colors.

Our short growing season and occasional late spring frosts can be a challenge, but Yarrow is quite hardy. With a little planning, you can easily enjoy its beauty for years to come within our 178-day growing season.

Starting Yarrow indoors is an option, especially if you want to get a head start on blooms. Start your seeds indoors in early to late February, about eight weeks before you plan to transplant them. This gives them a good head start before our late spring.

Use seed trays with a good seed-starting mix. Provide warmth (a heat mat is helpful) and plenty of light, either from a sunny window or grow lights. Bottom watering is a great way to keep the soil consistently moist without disturbing the tiny seeds.

Transplant your Yarrow seedlings outdoors in early April through early May, after the threat of a hard frost has passed. Be sure to harden them off first by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Space your plants 12-18 inches apart to allow for good air circulation. Even though we usually have even rainfall, be mindful of late frosts that can still hit in April. If you're eager for flowers the first year, consider purchasing established starts.

Direct sowing Yarrow is a simple and effective method, especially since we often have cool springs. Sow your seeds directly into the garden in mid April through late July. The soil temperature needs to be consistently above 60°F for good germination.

Prepare the soil by loosening it and removing any rocks (we know all about those in New England!). Scatter the seeds lightly over the surface and gently press them into the soil. Space them 12-18 inches apart or thin seedlings later. Direct sowing can be a bit slower than starting indoors, but it's a low-fuss option.

Yarrow is very drought-tolerant once established, which is great for our Northeast summers with moderate heat and humidity. However, getting it established requires some attention to watering.

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 feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or supplemental watering.

Water at the base of the plant rather than overhead to minimize the risk of fungal diseases in our moderate-to-humid climate. Overwatering can lead to floppy growth and root rot. Yellowing leaves are a sign of overwatering, while wilting leaves indicate underwatering. A light layer of mulch can help retain moisture and suppress weeds, but don't overdo it, as Yarrow prefers well-drained soil.

Deadheading is key to keeping your Yarrow blooming throughout the growing season. Remove spent flowers as soon as they fade 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 mid- October, cut back the foliage to the basal leaves. This will help the plant conserve energy over the winter. Divide the plants every 2-3 years to prevent them from becoming too aggressive.

You can expect your first harvest of Yarrow flowers in late June through late October, about 65 days after planting. Harvest the flowers when they are fully open and at their peak color, which is when they're best for drying.

Cut the stems just above a set of leaves, using sharp scissors or pruning shears. To encourage continued production, harvest regularly. As the first frost approaches in mid- October, harvest any remaining flowers before they are damaged by the cold.

Here are three common problems you might encounter with Yarrow in Zone 6A:

Spreading Aggressively

• What it looks like: Yarrow can quickly spread beyond its intended area, taking over garden beds.
• What causes it: Underground rhizomes allow it to spread rapidly, especially in fertile soil.
• How to fix/prevent it: Plant Yarrow in a contained area or use edging to prevent its spread. Regularly divide the plant to keep it in check. Remove unwanted shoots as soon 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.
• What causes it: Various fungi that thrive in warm days, cool nights, and moderate humidity, which we often experience in the Northeast. 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. 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).

Northeast Specific Challenges: The moderate heat, moderate-to-humid humidity, and even rainfall we experience in the Northeast can contribute to powdery mildew issues with Yarrow. Be sure to provide good air circulation and avoid overwatering to minimize these problems.

Yarrow makes a great companion plant for several vegetables and herbs in your Northeast garden. It attracts beneficial insects like ladybugs and hoverflies, which prey on aphids and other pests.

Yarrow is a good companion for tomatoes and peppers, as it attracts beneficial insects that help to pollinate the vegetables. It is also beneficial to herbs like rosemary and thyme, as it can improve their growth and flavor. Strawberries also benefit from being planted near yarrow, as it can help to deter pests. Avoid planting Yarrow near brassicas like cabbage and broccoli, as it can attract cabbage moths.