Yarrow in Zone 6A — Mountain West

Yarrow is a fantastic addition to any high-altitude garden. Its cheerful blooms bring long-lasting color, attract beneficial insects, and are perfect for drying. Plus, the cool nights even in summer here in the Mountain West really intensify the fragrance and color.

Our short growing season and alkaline soil present unique challenges, but Yarrow thrives with the right approach. With a 153-day growing season, you'll find that timing your planting and providing the right conditions will lead to a rewarding harvest.

Starting Yarrow indoors is an option, but not always necessary given its hardiness. If you're after blooms in the very first year, starting indoors gives you a head start. You have about a 3-week window from mid-February through early March to sow seeds indoors, about eight weeks before the last expected frost.

Use seed trays with a good seed-starting mix and provide warmth and plenty of light – a grow light is ideal. Be sure to water from the bottom to avoid damping off. Keep in mind that our late springs can sometimes be deceptive, so don't rush to put seedlings out too early!

Transplanting Yarrow seedlings outdoors happens mid-April through mid-May, once the danger of hard frost has passed. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense sun and cooler temperatures common in the Mountain West.

Space plants 12-18 inches apart in well-drained soil. Keep an eye on the weather forecast – a late cold snap or even hail can damage young transplants, so be ready to cover them if needed. Buying starts from a local nursery can guarantee flowers in the first year, as it gives you a more mature plant.

Direct sowing Yarrow is a simple and effective method, especially if you're not in a rush for first-year blooms. Sow seeds from early May through mid-July, after the soil has warmed up a bit. A soil temperature around 60-70°F is ideal for germination.

Prepare the soil by loosening it and removing any large rocks or debris. Scatter 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 once they are a few inches tall. Direct sowing means you're at the mercy of the weather, but Yarrow is fairly forgiving!

Yarrow is remarkably drought-tolerant once established, making it well-suited to our dry Mountain West climate. However, proper watering is key, especially during the first few weeks after planting.

During the initial establishment period, water deeply about once 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 plants are established, you can reduce watering frequency significantly. In our region, with its moderate summer heat and low humidity, you might only need to water every two to three weeks, or even less if we get decent rainfall. Water at the base of the plant to avoid wetting the foliage, further preventing fungal issues.

Signs of underwatering include wilting or drooping leaves. Overwatering, on the other hand, can lead to floppy growth and root rot. A light layer of mulch, such as pea gravel or shredded bark, can help retain moisture in the soil and regulate soil temperature, but avoid piling it up against the base of the plant.

Deadheading is crucial for encouraging continuous blooms throughout the season. As flowers fade, snip them off just below the flower head. This prevents the plant from putting energy into seed production and encourages new growth.

You can deadhead from early July through early October, whenever you see spent flowers. In the fall, after the first frost around early October, cut the plant back to its basal foliage (the leaves at the base of the plant). Yarrow can be a bit aggressive, so divide the plants every 2-3 years to keep them in check and prevent overcrowding.

You can expect your first harvest of Yarrow flowers from early July through early October, about 65 days after planting. The best time to harvest is when the flowers are fully open and at their peak color. This is when they have the highest concentration of essential oils and are most attractive to beneficial insects.

To harvest, simply cut the stems with sharp scissors or pruning shears, leaving a few inches of stem on the plant. For drying, hang the stems upside down in a cool, dark, and dry place until they are completely dry. Regular harvesting encourages the plant to produce more flowers, so don't be shy about cutting them! Even as the first frost approaches, you can still harvest any remaining blooms for drying.

Yarrow is generally a low-maintenance plant, but here are a few potential problems you might encounter in the Mountain West:

Spreading Aggressively

• What it looks like: Yarrow rapidly expands its territory, crowding out other plants.
• What causes it: Yarrow spreads via rhizomes (underground stems) and seeds. Our intense sun helps it grow vigorously, and our alkaline soil doesn't deter it.
• How to fix/prevent it: Plant Yarrow in a contained area, such as a raised bed or surrounded by edging. Divide the plants every 2-3 years to control their spread. 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.
• What causes it: Various fungi 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.

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.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity generally benefit Yarrow, reducing the risk of many fungal diseases. However, the intense UV radiation can sometimes stress the plants, making them more susceptible to pests. Ensuring adequate watering and providing some afternoon shade during the hottest part of the day can help mitigate this issue.

Yarrow is a great companion plant for many vegetables and herbs in our Mountain West gardens. It attracts beneficial insects like ladybugs and lacewings, which help control pests.

Good companions:

• Tomato and Pepper: Yarrow attracts beneficial insects that prey on common tomato and pepper pests like aphids and whiteflies.
• Herbs: Yarrow enhances the essential oils and overall health of many herbs, especially those in the mint family.
• Strawberry: Yarrow repels some strawberry pests and attracts pollinators, leading to increased fruit production.

Bad companions:

• Avoid planting Yarrow near plants that prefer acidic soil, as Yarrow thrives in alkaline conditions.