Yarrow in Zone 3B — Mountain West

Yarrow is a fantastic addition to any Mountain West garden. Its vibrant flowers bring color and attract beneficial insects to your garden. Plus, the cool nights we get here enhance its fragrance, making it a joy to grow and use in bouquets, dried arrangements, or even herbal remedies.

Our short growing season and alkaline soil can be a challenge, but Yarrow is surprisingly resilient. With a little planning, you can easily fit its 65-day maturity into our 108-day window, and its drought tolerance is perfect for our dry climate.

Starting Yarrow indoors is an option, but honestly, it's often easier to direct sow or transplant starts. If you want a head start, begin in early to late March, roughly 8 weeks before you'd like to transplant. Use seed trays with a good seed-starting mix and provide warmth and light.

Bottom watering is your friend – set the trays in a shallow pan of water until the surface soil is moist. Remember, spring in the Mountain West can be unpredictable, so keep an eye on the weather before you move seedlings outdoors.

Transplant your Yarrow seedlings outdoors in mid May through early June, after the risk of 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 intense sun and cooler nights we experience.

Space your plants 12-18 inches apart. Given that Yarrow is a perennial, buying starts can get you flowers in that first year. Be mindful of late-season snow or hail, which can still happen even in late spring.

Direct sowing Yarrow is straightforward. Wait until late May through late June, when the soil has warmed up a bit. Prepare the soil by loosening it and removing any rocks or debris. Yarrow isn't too picky, but well-drained soil is a must.

Scatter the seeds lightly over the surface and gently press them into the soil. Keep the area moist until the seedlings emerge. Thin them to 12-18 inches apart once they're a few inches tall. Direct sowing means waiting longer for blooms, but it's a low-effort way to get started.

Yarrow thrives on neglect, which is great for our dry Mountain West climate! Once established, it's very drought-tolerant. You'll mainly need to water during its first year to help it get settled.

During the peak of summer (typically July and August), give your Yarrow about ½ inch of water per week if there hasn't been any rainfall. Use the "finger test" – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Water at the base of the plant to avoid wetting the foliage, which helps prevent fungal issues in our low-humidity environment.

Signs of underwatering include wilting or yellowing leaves, while overwatering can lead to floppy growth and root rot. A light layer of gravel mulch around the base of the plant can help conserve moisture and prevent soil splash.

Pruning Yarrow is simple and keeps it looking its best. Regularly deadhead spent flowers throughout the growing season to encourage a second flush of blooms. Just snip off the flower heads below the lowest set of petals.

In late fall, after the first frost around early September, cut the plant back to its basal foliage. This helps it conserve energy over the winter. Yarrow can be a bit aggressive, so divide the clumps every 2-3 years to keep it in check.

You can expect your first harvest of Yarrow flowers in late July through mid September, depending on when you planted. The best time to harvest is when the flowers are fully open and at their peak color. This is when they have the most fragrance and beneficial properties.

To harvest, simply cut the stems just above a leaf node. You can then bundle the stems together and hang them upside down in a cool, dark, and dry place to dry for later use in teas, crafts, or dried flower arrangements. Continued harvesting encourages more blooms.

As the first frost approaches in early September, harvest any remaining flowers before they get damaged. Even if they aren't fully open, they will still dry nicely.

Here are the most common problems you might encounter with Yarrow in the Mountain West:

Aggressive Spreading

• What it looks like: Yarrow starts popping up in areas where you didn't plant it, quickly forming dense colonies.
• What causes it: Yarrow spreads via rhizomes (underground stems), and it's quite vigorous. Our intense sun and well-drained soil encourage its growth.
• How to fix/prevent it: Plant Yarrow in a contained area or use edging to prevent it from spreading. Regularly divide the plant every few years to keep it in check. Be diligent about removing unwanted seedlings.

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 by spacing plants properly and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays can help. A 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: A strong water spray knocks them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap can be used for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer, as it attracts them.

Mountain West Specific Challenges: Our moderate-at-altitude summer heat and low humidity generally benefit Yarrow, making it less susceptible to fungal diseases compared to more humid climates. However, our dry rainfall means you'll need to be mindful of providing adequate moisture, especially during the establishment phase. Alkaline soil is generally fine for Yarrow.

Yarrow is a great companion plant for several vegetables and herbs in your Mountain West garden.

• Tomato & Pepper: Yarrow attracts beneficial insects like ladybugs and hoverflies, which prey on aphids and other pests that can damage tomatoes and peppers.
• Herbs: Planting Yarrow near herbs like rosemary, thyme, and oregano can enhance their essential oil production, making them more flavorful and fragrant.
• Strawberry: Yarrow is believed to improve the overall health and vigor of strawberry plants.

Avoid planting Yarrow near plants that prefer very rich, moist soil, as Yarrow thrives in drier conditions.