Yarrow in Zone 9B — Desert Southwest

Yarrow is a fantastic addition to any Desert Southwest garden. Its feathery foliage and clusters of colorful flowers add beauty, attract beneficial insects, and the blooms make excellent dried arrangements for year-round enjoyment. Plus, it's incredibly drought-tolerant once established, perfect for our arid climate.

Desert gardening has its challenges, of course. Extreme heat and alkaline soil can be tough on some plants, but Yarrow thrives with the right approach. With our long 313-day growing season, you have plenty of time to get it established and enjoy its benefits.

Starting Yarrow indoors isn't strictly necessary in our climate, but it can give you a head start, especially if you want blooms the first year. Begin sowing seeds indoors from mid November through mid December, about eight weeks before you plan to transplant.

Use seed trays with a well-draining seed-starting mix. Keep the soil consistently moist, but not waterlogged, using bottom watering to avoid damping off. Provide warmth and plenty of light, and remember that the early start takes advantage of our very-early spring.

Transplant your Yarrow seedlings outdoors from late January through mid February, after hardening them off for about a week. Gradually expose them to increasing amounts of sunlight and wind each day.

Space the plants 12-18 inches apart in a sunny location with well-drained soil. Even though this is typically our mildest time of year, watch out for any late frosts and protect your young plants if needed. You can also buy established Yarrow starts from your local nursery for flowers the first year.

Direct sowing Yarrow is a simple and effective method in the Desert Southwest. Sow seeds directly into the garden from early February through late September.

Prepare the soil by loosening it and removing any rocks or debris. Yarrow isn't picky about soil, but it does need good drainage. Lightly sprinkle the seeds on the surface and gently press them into the soil. Keep the soil consistently moist until the seedlings emerge. Thin seedlings to 12-18 inches apart.

Yarrow is exceptionally drought-tolerant once it's established, making it ideal for water-wise desert gardening. However, it does need regular watering during its first year to develop a strong root system.

During the cooler months (late fall, winter, early spring), water deeply every 2-3 weeks, or when the top two inches of soil feel dry to the touch (use the "finger test"). As temperatures rise in late spring and summer, increase watering to once a week, or more frequently during periods of extreme heat. During the monsoon season, keep an eye on the rainfall and adjust your watering schedule accordingly.

Water at the base of the plant to avoid wetting the foliage, which can increase the risk of fungal diseases in our arid environment. Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to root rot and floppy growth. Mulching around your plants with compost or gravel helps retain moisture and suppress weeds.

Regular pruning helps keep your Yarrow plants healthy and productive. Deadhead spent flowers throughout the growing season to encourage more blooms. Simply snip off the faded flower heads just below the next set of leaves.

In the late fall, after the first frost around mid- December, cut the plants back to their basal foliage. This helps tidy up the garden and prepares the plants for winter dormancy. Yarrow can be aggressive, so divide the clumps every 2-3 years to prevent overcrowding.

You can expect your first Yarrow harvest around mid April through late December, about 65 days after planting. Harvest the flowers for drying when they are fully open and their color is at its peak.

Cut the stems just above a set of leaves, using sharp scissors or pruners. Gather the stems into small bundles and hang them upside down in a cool, dark, and dry place to dry. To encourage continued production, harvest flowers regularly throughout the season. Even as the first frost approaches in mid- December, you can often still harvest some late-blooming flowers.

Yarrow is generally a low-maintenance plant, but here are a few common problems to watch out for in the Desert Southwest:

Spreads Aggressively

• What it looks like: Yarrow rapidly expands beyond its intended planting area, crowding out other plants.
• What causes it: Rhizomatous roots spread quickly, especially in well-drained soil. Our long growing season encourages rapid expansion.
• How to fix/prevent it: Plant Yarrow in a contained area or divide clumps every 2-3 years to control its spread. Remove unwanted plants promptly.

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. Dry leaf surfaces actually favor it.
• How to fix/prevent it: Improve air circulation by spacing plants adequately and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays can help. Plant resistant varieties.

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: Strong water spray knocks them off. Encourage ladybugs and lacewings. Insecticidal soap for heavy infestations. Avoid excess nitrogen fertilizer.

Desert Southwest Specific Challenges: Our extreme heat and intense sunlight can stress Yarrow, making it more susceptible to pests and diseases. Providing afternoon shade during the hottest months can help. Although Yarrow is drought-tolerant, consistent watering during establishment is crucial, especially given our alkaline soil. Monsoon moisture, while welcome, can also create conditions favorable for powdery mildew if air circulation is poor.

Yarrow makes a great companion plant in the Desert Southwest garden. It attracts beneficial insects that help control pests on other plants.

Good companions for Yarrow include:

• Tomatoes and Peppers: Yarrow attracts predatory insects like ladybugs and lacewings, which feed on aphids that can plague tomatoes and peppers.
• Herbs: Planting Yarrow near herbs like rosemary and thyme can enhance their flavor and growth.
• Strawberries: Yarrow can help deter pests that attack strawberries, such as spider mites.

Avoid planting Yarrow near plants that require consistently moist soil, as Yarrow prefers drier conditions.