Yarrow in Zone 5A — Mountain West

Yarrow is a fantastic addition to any Zone 5A Mountain West garden. Its vibrant flowers bring welcome color to our landscapes, and its herbal properties make it a versatile plant for teas and salves. Plus, yarrow attracts beneficial insects, supporting a healthy garden ecosystem. The intense sunlight and cool nights of our high-altitude climate actually enhance the flavor and potency of herbs like yarrow.

High altitude gardening in the Mountain West presents unique challenges, including a short growing season and intense UV. But with yarrow's relatively quick maturity and frost tolerance, timing your planting is straightforward. You have a solid 138-day growing season to work with, so even if you start seeds indoors, you'll still have plenty of time to enjoy its blooms.

Starting yarrow indoors in our region is an option, especially if you want a head start on blooms the first year. Begin in late February through mid March, giving the seedlings about 8 weeks to develop before transplanting. This helps ensure you get flowers in the first year.

Use seed trays with a good seed-starting mix, providing warmth (around 70°F) and plenty of light – a grow light works wonders in our climate, especially with our late spring starts. Bottom watering is a good idea to keep the soil consistently moist without damping off. Keep in mind that our late spring can bring unexpected temperature swings, so keep an eye on your seedlings and adjust as needed.

Transplanting yarrow outdoors should happen in late April through late May, after the last expected frost. Before moving your seedlings outside permanently, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to our intense sun and cooler nights.

Space your yarrow plants 12-18 inches apart to allow for their clumping growth habit. While you can grow yarrow from seed, buying starts from a local nursery may give you blooms in the first year. Keep an eye on the weather forecast – late spring snow or hail isn't uncommon in the mountains, so be ready to protect your transplants if necessary.

Direct sowing yarrow is a simple method for our region, and the timing is quite forgiving. Sow seeds directly into your garden beds from early May through early July. The soil needs to be workable and ideally around 60-70°F for best germination.

Prepare the soil by loosening it and removing any rocks or debris. Scatter the seeds lightly over the surface and gently press them into the soil. Thin seedlings to 12-18 inches apart once they emerge. Direct sowing might delay flowering until the second year, but it's a low-effort way to establish a healthy yarrow patch.

Yarrow thrives on neglect, which is perfect for our dry Mountain West climate. Once established, it's very drought-tolerant, so avoid overwatering. In our region, with typical summer highs around 85°F and low humidity, less is definitely more when it comes to watering yarrow.

During the first few weeks after planting (whether transplant or direct sow), water regularly to help establish a strong root system. After that, let the soil dry out between waterings. Use the "finger test" – stick your finger about 2 inches into the soil; if it's dry, it's time to water. As a general guideline, aim for about 1 inch of water per week, especially during the hottest stretches of summer.

Water at the base of the plant rather than overhead to minimize the risk of fungal diseases in our dry climate. Signs of underwatering include wilting leaves and stunted growth. Overwatering, on the other hand, can lead to floppy growth and root rot. Mulching around your yarrow plants with gravel or shredded bark can help retain moisture in the soil and suppress weeds.

Pruning yarrow is straightforward and helps keep 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 spent flowers.

This not only improves the plant's appearance but also prevents it from self-seeding too aggressively. In late fall, after the first frost around late September, cut the plant back to its basal foliage. This prepares it for winter dormancy. Yarrow can be aggressive, so divide the plant every 2-3 years to keep it in check.

You can expect your first yarrow harvest from mid July through early October in our region, about 65 days after planting. Harvest the flowers for drying when they are fully open and at their peak color. These are excellent dried flowers.

Cut the stems just below the flower heads, ideally in the morning after the dew has dried. Hang the stems upside down in a cool, dark, and dry place to dry completely. Regular harvesting encourages continued flower production throughout the season. Even as the first frost approaches in late September, you can still harvest any remaining flowers for drying.

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

Spreads Aggressively

• What it looks like: Yarrow quickly expands beyond its intended space, sending out runners and crowding out other plants.
• What causes it: Yarrow is a vigorous grower and can spread easily, especially in well-drained soil.
• How to fix/prevent it: Plant yarrow in a contained area or regularly divide the plant to control its spread. Deadheading spent flowers also helps prevent self-seeding.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems. Leaves curl, yellow, and die. Reduces plant vigor.
• 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. 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).

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry rainfall can actually be beneficial for yarrow, reducing the risk of many fungal diseases. However, the intense UV radiation can stress the plants, so providing some afternoon shade during the hottest part of the day can be helpful, especially for young plants. Be sure to monitor for aphids, as they can thrive even in our dry climate.

Yarrow makes a great companion plant in the Mountain West garden. Its aromatic foliage repels some pests and attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other garden pests.

Good companions include tomatoes and peppers, as yarrow can help protect them from pests. Herbs like rosemary and thyme also benefit from yarrow's presence. Strawberries enjoy yarrow as a neighbor, because it attracts pollinators. Avoid planting yarrow near brassicas (cabbage, broccoli, cauliflower), as it can sometimes inhibit their growth.