Yarrow in Zone 10A — Desert Southwest

Yarrow is a fantastic addition to any Desert Southwest garden. It's beautiful, drought-tolerant, and attracts beneficial insects to your garden. Plus, it's a great dried flower, adding a touch of desert charm to your home.

We know the extreme heat and alkaline soil can be tough on plants, but with proper timing and care, yarrow thrives here. Our long growing season, stretching over 330 days, gives you plenty of opportunity for success with this hardy perennial.

Starting yarrow indoors isn't essential, but it gives you a head start, especially if you want blooms in the first year. Begin in early to late November, about eight weeks before you plan to transplant. Use seed trays with a well-draining seed-starting mix and provide warmth and bright light.

Bottom watering is key to avoid damping off. Set the tray in a shallow container of water, allowing the soil to absorb moisture from the bottom. Remember, with our very-early spring character, getting a head start indoors can pay off.

Transplant your yarrow seedlings outdoors in early January through early February. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intensity of the desert sun.

Space plants 12-18 inches apart in well-draining soil. Even though we have mild winters, keep an eye out for unexpected dips in temperature. You can buy starts for flowers the first year.

Direct sowing yarrow is an easy option in our climate, thanks to our two growing seasons. Sow seeds mid-January through early October. The monsoon moisture can really help with germination.

Prepare the soil by loosening it and removing any large clumps. Scatter seeds thinly over the surface and lightly press them into the soil. Keep the soil consistently moist until seedlings emerge, but be careful not to overwater. Thin seedlings to 12-18 inches apart.

Yarrow is incredibly drought-tolerant once established, making it perfect for desert gardening. However, it does need consistent watering, especially during its first year. A good rule of thumb is to water deeply but infrequently.

During the hotter months, from late spring through summer, water about once a week, providing about ½ inch of water. Use the finger test: if the top two inches of soil are dry, it's time to water. During the cooler fall and winter months, you can reduce watering to every two to three weeks. Water at the base of the plant to avoid wetting the foliage, which can lead to problems even in our arid climate.

Signs of underwatering include wilting or yellowing leaves. Overwatering, on the other hand, can cause floppy growth and root rot. A layer of gravel mulch around the base of the plant helps retain moisture and prevents soil from splashing onto the foliage.

Deadheading is essential for keeping your yarrow looking its best and encouraging more blooms. Throughout the growing season, snip off spent flowers just below the flower head. This directs the plant's energy into producing new flowers instead of seeds.

In late fall, after the first frost around late December, cut the plant back to its basal foliage. This helps tidy up the plant for winter and encourages fresh growth in the spring. Yarrow can be aggressive, so divide it every 2-3 years to keep it in check.

You can expect your first yarrow harvest about 65 days after planting, from late March through early January, depending on when you planted. Harvest flowers for drying when they are fully open and their color is at its peak. These make excellent dried flowers.

To harvest, simply cut the stems just above a leaf node. This encourages the plant to produce more flowers. For continuous production, harvest regularly throughout the growing season. As the first frost approaches in late December, harvest any remaining flowers to dry them for winter enjoyment.

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

Aggressive Spreading:

• What it looks like: Yarrow quickly expands beyond its intended area, crowding out other plants.
• What causes it: Yarrow spreads via rhizomes (underground stems), and in our long growing season, it has ample time to spread.
• How to fix/prevent it: Plant yarrow in a contained area or use edging to prevent rhizomes from spreading. Dig up and divide the plant every 2-3 years to control its size.

Powdery Mildew:

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves may curl, yellow, and eventually die.
• What causes it: While our climate is arid, powdery mildew can still occur, especially during periods of moderate humidity and cool nights.
• How to fix/prevent it: Improve air circulation by spacing plants adequately and pruning as needed. Remove affected leaves promptly. Apply neem oil or potassium bicarbonate sprays. 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 insects on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Aphids thrive in warm weather and can multiply rapidly.
• How to fix/prevent it: Knock aphids off plants with a strong spray of water. Encourage beneficial insects like ladybugs and lacewings. Use insecticidal soap or neem oil for heavy infestations.

Desert Southwest Specific Challenges: The extreme heat and intense sun can stress yarrow, making it more susceptible to problems. While yarrow is drought-tolerant, prolonged periods without water can also weaken the plant. The monsoon moisture can create conditions favorable for powdery mildew. Regular monitoring and preventative measures are key to success.

Yarrow makes a great companion plant in the Desert Southwest garden. It attracts beneficial insects like ladybugs and hoverflies, which prey on pests like aphids.

Good companions include tomatoes and peppers, as the beneficial insects yarrow attracts will help keep these plants pest-free. Herbs like rosemary and thyme also benefit from yarrow's presence. Strawberries also enjoy the company of yarrow, as it can help deter certain pests. Avoid planting near plants that prefer very rich, moist soil, as yarrow thrives in drier conditions and can compete for resources.