Yarrow in Zone 7B — Desert Southwest

Yarrow is a fantastic addition to any Desert Southwest garden. Its feathery foliage and clusters of colorful blooms not only add beauty, but also attract beneficial insects. Plus, you can dry the flowers for arrangements that bring a touch of your garden indoors.

While our extreme heat and alkaline soil can be tough on some plants, Yarrow is surprisingly resilient. With proper timing and a little attention, you can enjoy its beauty and benefits throughout our long, 245-day growing season.

Starting Yarrow indoors in the Desert Southwest is an option, especially if you want a head start on blooms the first year. Begin in late December through mid January, about eight weeks before you plan to transplant. Use seed trays with a good seed-starting mix and provide warmth, either with a heat mat or a warm location in your home.

Keep the soil consistently moist by bottom watering. This helps prevent damping off, which can be a problem with seedlings. Because our spring arrives very-early, starting indoors gives you a jump.

Transplant your Yarrow seedlings outdoors in early to late March. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents shock from our intense Desert Southwest sun.

Plant them 12-18 inches apart in well-draining soil. Keep an eye on the weather at this time of year; we can still get some unexpected temperature swings, so be ready to cover them if a late frost threatens. Buying starts lets you enjoy flowers the first year.

Direct sowing Yarrow is a simple and effective method in the Desert Southwest. Sow the seeds outdoors from mid March through late August. Prepare the soil by loosening it and removing any rocks or debris.

Yarrow prefers slightly cooler soil temperatures for germination, so aim for the earlier end of that window if possible. Lightly press the seeds into the soil, keeping them about 12-18 inches apart. Direct sowing is easy, but you'll wait longer for flowers.

Yarrow is very drought-tolerant once established, making it perfect for our arid Desert Southwest climate. During the extreme heat of summer, even drought-tolerant plants need supplemental watering. Newly planted Yarrow needs more frequent watering to get established.

Water deeply but infrequently. 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.

Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases even in our low humidity. Signs of underwatering include wilting or yellowing leaves, while overwatering can lead to floppy growth and root rot. Adding a layer of rock mulch will help retain moisture while reflecting the sun.

Pruning Yarrow is essential for maintaining its appearance and encouraging continued blooms. Deadhead spent flowers throughout the growing season to promote a second flush of blossoms. Simply snip off the flower heads just below the lowest petals.

In the fall, after the first frost around mid- November, 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 in check.

You can expect your first Yarrow harvest from mid May through late November in our Zone 7B Desert Southwest garden. Harvest the flowers for drying when they are fully open and at their peak color. This is usually about 65 days after planting.

Cut the stems in the morning after the dew has dried, leaving several inches of stem on the plant to encourage new growth. Hang the cut stems upside down in a cool, dark, and dry place to dry.

Continue harvesting throughout the season to encourage more blooms. As the first frost approaches in mid- November, harvest any remaining flowers before they are damaged by the cold.

Here are the top 3 problems you might encounter with Yarrow 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: Rhizomes spread underground, sending up new shoots. Our long growing season allows for extended spread.
• How to fix/prevent it: Plant in a contained area or use edging to restrict rhizome growth. Regularly dig up and divide the plant to control its spread.

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. Our monsoon season can create brief periods of higher humidity.
• How to fix/prevent it: Improve air circulation through spacing and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays help. Milk spray (1 part milk to 9 parts water) is surprisingly effective.

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. Our extended warm season allows for multiple generations.
• How to fix/prevent it: Strong water spray knocks them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap for heavy infestations. Neem oil works systemically.

Desert Southwest Specific Challenges: The extreme heat of our summers can stress Yarrow, making it more susceptible to pests and diseases. The arid humidity can also lead to powdery mildew if plants are not properly spaced. However, Yarrow's drought tolerance makes it well-suited to our water-scarce environment.

Yarrow makes a great companion plant in the Desert Southwest garden. It attracts beneficial insects like ladybugs and lacewings, which prey on pests that can damage tomatoes and peppers. Plant it near these veggies for natural pest control.

Yarrow also benefits herbs like rosemary and thyme by attracting pollinators and improving soil health. It can even be planted near strawberries, as it is believed to enhance their flavor. Avoid planting Yarrow near plants that prefer very rich, moist soil, as Yarrow thrives in drier conditions.