Yarrow in Zone 3A — Mountain West

Yarrow is a fantastic addition to any Zone 3A Mountain West garden. The bright, cheerful flowers add beauty, attract beneficial insects, and are excellent for drying. Plus, the cool nights even in summer seem to intensify their fragrance, making them a joy to have around.

Our high altitude gardening comes with challenges like intense sun and a short growing season, roughly 96 days. But don't worry, Yarrow is well-suited to our climate, and with the right timing, you'll have no problem growing it successfully.

Starting Yarrow indoors is an option, but not always necessary, especially with our short season. If you want a head start, particularly for blooms the first year, start seeds indoors from mid-March through early April, about 8 weeks before you plan to transplant.

Use seed trays with a good seed-starting mix. Keep the soil consistently moist, using bottom watering to avoid disturbing the tiny seeds. Provide warmth and plenty of light – a grow light is ideal, as our late spring can be unpredictable.

Transplanting Yarrow outdoors should be done from mid-May through mid-June, after the risk of hard frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Choose a sunny spot with well-drained soil and space plants 12-18 inches apart. Be prepared for possible late-season cold snaps or even hail. If you're impatient for blooms the first year, consider buying starts from a local nursery.

Direct sowing Yarrow is definitely possible in our climate, and can be a great option. Sow seeds directly into the garden from early to mid-June, once the soil has warmed up.

Prepare the soil by loosening it and removing any weeds. Gently press the seeds into the soil surface, but don't bury them too deeply, as they need light to germinate. Keep the soil consistently moist until seedlings emerge. Thin seedlings to 12-18 inches apart.

Yarrow thrives on neglect, which is perfect for our dry Mountain climate. Once established, it's very drought-tolerant and prefers drier conditions. Overwatering can lead to floppy growth and other problems.

During the first few weeks after transplanting or direct sowing, water regularly to help the plants establish. After that, water deeply but infrequently, only when the top 2 inches of soil feel dry to the touch – the "finger test". In our low-humidity environment, this might mean watering every 1-2 weeks, or even less frequently during cooler periods. Aim for about 1 inch of water per week when watering is needed.

Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases, even in our low-humidity conditions. Signs of underwatering include wilting or yellowing leaves. Overwatering can cause the stems to become weak and the leaves to turn pale green. A light mulch of gravel or pine needles can help conserve moisture and suppress weeds.

Pruning Yarrow is simple and helps encourage continued blooming. Throughout the growing season, deadhead spent flowers to encourage a second flush of blooms. Simply cut the flower stems back to the next set of leaves.

Toward the end of the season, after the first frost around early September, cut the plant back to its basal foliage. This helps tidy up the garden and prepares the plant for winter dormancy. Since Yarrow can be aggressive, divide the clumps every 2-3 years to keep it under control.

You can expect your first Yarrow harvest from early August through mid-September, about 65 days after planting. Harvest the flowers for drying when they are fully open and the petals are firm.

Cut the stems at the base of the plant, just above a set of leaves. To dry the flowers, bundle the stems together and hang them upside down in a cool, dark, and dry place. Regular harvesting will encourage continued production throughout the season. As the first frost approaches, harvest any remaining flowers before they are damaged by the cold.

Here are some common problems you might encounter growing Yarrow in the Mountain West:

Spreading Aggressively

• What it looks like: Yarrow plants spreading beyond their intended space, crowding out other plants.
• What causes it: Yarrow is a vigorous grower and can spread through rhizomes (underground stems). Our intense sun and well-drained soil can encourage rapid growth.
• 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. Be diligent about removing unwanted seedlings.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves may curl, yellow, and die.
• What causes it: Fungal disease that thrives in warm days, cool nights, and moderate humidity. Ironically, dry leaf surfaces favor it.
• How to fix/prevent it: Improve air circulation around plants by spacing them properly and pruning. Remove and dispose of affected leaves. Neem oil or potassium bicarbonate sprays can help. A milk spray (1 part milk to 9 parts water) can also be effective.

Aphids

• What it looks like: Clusters of tiny green, black, or white soft-bodied insects on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Sap-sucking insects that reproduce rapidly, especially in warm weather.
• How to fix/prevent it: Knock aphids off plants with a strong spray of water. Encourage natural predators like ladybugs and lacewings. Use insecticidal soap for heavy infestations. Neem oil also works.

Mountain West Specific Challenges: While our low humidity generally helps prevent fungal diseases, the intense UV radiation can stress plants, making them more susceptible to pests. Be sure to provide adequate water, especially during hot, dry spells, and consider using shade cloth during the hottest part of the day.

Yarrow is a great companion plant for many vegetables and herbs in the Mountain West garden. It attracts beneficial insects like ladybugs and lacewings, which prey on pests that can damage other plants.

Good companions include tomatoes and peppers, as Yarrow can help repel common pests like tomato hornworms and aphids. It also works well with herbs like rosemary and thyme, enhancing their growth and flavor. Strawberries also benefit from Yarrow's presence, as it can help deter pests and improve pollination. Avoid planting Yarrow near plants in the cabbage family, like broccoli or kale, as it can attract cabbage moths.