Yarrow in Zone 8A — Desert Southwest

Yarrow is a fantastic addition to any Desert Southwest garden. Its feathery foliage and clusters of vibrant flowers bring beauty, attract beneficial insects, and offer a satisfying sense of accomplishment. Plus, Yarrow thrives in our arid climate, asking little in return for its striking display.

While the extreme heat and alkaline soil of the Desert Southwest can be challenging, Yarrow is well-suited to our conditions. With a little planning and attention to its needs, you can enjoy its beauty throughout our long 265-day growing season.

Starting Yarrow indoors is optional here in the Desert Southwest, given our extended growing seasons. However, if you're eager to get a head start, aim to sow seeds indoors from mid December through early January, about eight weeks before the ideal transplanting window.

Use seed trays with a well-draining seed-starting mix. Keep the soil consistently moist (bottom watering is great for this) and provide a warm location with ample light – a sunny windowsill or grow lights work well. Keep in mind that our very-early spring weather can be unpredictable, so starting indoors offers a buffer against any late cold snaps.

Transplant your Yarrow seedlings outdoors from mid February through mid March. This timing allows the plants to establish themselves before the extreme heat arrives. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Choose a sunny spot with well-draining soil, spacing plants 12-18 inches apart. While the weather is usually mild during this time, be prepared to protect young transplants from unexpected frosts. You might even consider buying starts from a local nursery. This is an easy way to get flowers the first year since Yarrow is a perennial.

Direct sowing Yarrow is certainly possible in the Desert Southwest and can be quite successful, thanks to our long growing season. Sow seeds directly into the garden from early March through early September.

Prepare the soil by loosening it and removing any rocks or debris. Yarrow prefers well-drained soil and doesn't need particularly rich conditions. Gently press the seeds into the soil, keeping them about 12-18 inches apart. Keep the soil consistently moist until germination, which usually takes about 10-14 days. Just be aware that direct sowing later in the season means the young plants will have to face the extreme heat earlier.

Yarrow is incredibly drought-tolerant once established, making it an ideal choice for water-wise desert gardening. However, proper watering is still essential, especially during the initial establishment phase.

During the spring and fall growing seasons, water deeply but infrequently, allowing the soil to dry out between waterings. Use the finger test: if the top two inches of soil are dry, it's time to water. Aim for about 1 inch of water per week, depending on rainfall. During the monsoon season, you may not need to water at all.

In the extreme heat of summer, Yarrow will appreciate supplemental watering, but be careful not to overdo it. Overwatering can lead to floppy growth and root rot. Water at the base of the plant rather than overhead to minimize fungal diseases in our arid climate. Signs of underwatering include wilting and dry, crispy leaves, while overwatering can manifest as yellowing leaves and mushy stems. A light layer of gravel mulch around the base of the plant can help conserve moisture and prevent soil splashing.

Pruning Yarrow is simple and helps to encourage continuous blooming. Throughout the growing season, deadhead spent flowers to promote new growth and prevent the plant from going to seed.

Simply snip off the faded flower heads just below the lowest flower. In the late fall, after the first frost around late November, cut the plant back to its basal foliage. This will help to tidy up the garden and prepare the plant for winter dormancy. Remember that Yarrow can be aggressive, so divide the clumps every 2-3 years to keep it in check.

You can expect your first Yarrow harvest about 65 days after planting, which translates to early May through early December in our Desert Southwest climate. The best time to harvest Yarrow flowers for drying is when they are fully open and at their peak color.

Cut the stems just above a leaf node, using sharp scissors or pruners. Bundle the stems together and hang them upside down in a cool, dark, and dry place to dry. To encourage continued production, harvest regularly throughout the season. As the first frost approaches in late November, harvest any remaining flowers to dry or use fresh.

Here are some common problems you might encounter with Yarrow in the Desert Southwest:

Aggressive Spreading

• What it looks like: Yarrow plants expanding rapidly beyond their intended space, crowding out other plants.
• What causes it: Yarrow spreads through rhizomes (underground stems), and in our long growing season, it has plenty of time to colonize new areas.
• How to fix/prevent it: Plant Yarrow in a contained area or raised bed. Divide the plants every 2-3 years to control their spread. Regularly remove unwanted shoots that pop up.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves may curl, yellow, and die.
• What causes it: Fungi that thrive in warm days, cool nights, and moderate humidity. While our humidity is generally low, monsoon season can create favorable conditions.
• How to fix/prevent it: Improve air circulation by spacing plants properly. Remove affected leaves promptly. Neem oil or potassium bicarbonate sprays can help. A milk spray (1 part milk to 9 parts water) is surprisingly effective.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects 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.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap can be used for heavy infestations.

Desert Southwest Specific Challenges: The extreme heat and arid humidity can stress Yarrow, making it more susceptible to pests and diseases. The monsoon rainfall, while welcome, can also create favorable conditions for powdery mildew. Monitor your plants closely, especially during periods of extreme weather, and take action promptly to address any issues.

Yarrow is a great companion plant for many vegetables and herbs in the Desert Southwest garden.

Good companions include tomatoes and peppers: Yarrow attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other pests that can damage these crops. It also helps to improve soil health. Herbs like rosemary, thyme, and oregano also benefit from Yarrow's presence. Its strong scent can deter pests, and it attracts pollinators that can improve yields. Strawberries enjoy Yarrow as a companion because it is believed to enhance their flavor and vigor.

Avoid planting Yarrow near plants that prefer very rich, moist soil, as Yarrow thrives in drier conditions and can compete for resources.