Yarrow in Zone 8B — Southern California

Yarrow is a fantastic addition to any Southern California garden. Its feathery foliage and clusters of vibrant flowers bring beauty and attract beneficial insects, crucial for a healthy garden ecosystem. Plus, it's drought-tolerant, perfect for our water-wise landscapes and long, dry summers inland.

Our Mediterranean climate offers a long growing season, but it also presents challenges like water restrictions and intense summer heat. However, with careful planning and timing, you can successfully grow Yarrow and enjoy its blooms from late spring well into fall, making the most of our 298-day growing season.

Starting Yarrow indoors in our mild climate is possible, but usually not necessary. You'll get a head start if you want blooms the first year, though. If you choose to start indoors, sow seeds from late November through late December, about eight weeks before you'd transplant them.

Use seed trays with a well-draining seed starting mix. Keep the soil consistently moist, using bottom watering to avoid disturbing the tiny seeds. Provide warmth and plenty of light, especially since our spring character: very-early. A simple grow light works wonders.

Transplant your Yarrow seedlings outdoors from early February through early March. This gives them time to establish before the summer heat inland arrives. 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 the plants 12-18 inches apart. Our winters are mild, but watch out for unexpected cold snaps and protect young plants if needed. Buying starts is a great way to get flowers the first year, since Yarrow is a perennial.

Direct sowing Yarrow is a simple and effective method, especially in our forgiving climate. You can sow seeds directly into the garden from mid February through late September. This gives you a wide window to experiment with.

Prepare the soil by loosening it and removing any weeds. Yarrow prefers well-drained soil, so amend heavy clay soils with compost or other organic matter. Sow seeds thinly and lightly cover them with soil. Keep the soil consistently moist until germination, then thin seedlings to 12-18 inches apart.

Yarrow is a very drought-tolerant plant once established, making it ideal for our Southern California gardens, especially with water restrictions. However, it still needs some water, especially during its first year and during periods of intense heat. Overwatering leads to floppy growth, so err on the side of dryness.

During the cooler months (fall, winter, and spring), water deeply but infrequently, allowing the soil to dry out between waterings. Use the "finger test" – stick your finger about two inches deep into the soil. If it feels dry, it's time to water. In the summer heat inland, you might need to water once or twice a week, providing about 1 inch of water each time. Water at the base of the plant to avoid wetting the foliage, especially in our low-to-moderate humidity, to minimize fungal issues.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can cause yellowing leaves and root rot. Mulching around the base of the plant with organic matter like wood chips or straw helps retain moisture in our hot and dry conditions and suppresses weeds.

Pruning Yarrow is simple and helps encourage more blooms. Deadhead spent flowers regularly throughout the growing season to promote a second flush of flowers. Simply snip off the flower heads just below the lowest set of leaves.

In the fall, after the first frost around early December, cut the plant back to its basal foliage. This helps tidy up the garden and prepares the plant for winter dormancy. Yarrow can be aggressive, so divide the clumps every 2-3 years to prevent them from taking over your garden.

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

To harvest, simply cut the stems just above a leaf node. This encourages the plant to produce more flowers. Yarrow provides continuous blooms throughout the growing season, so you can harvest regularly.

As the first frost approaches in early December, harvest any remaining flowers before they are damaged by the cold. You can dry them indoors to enjoy their beauty throughout the winter. Yarrow attracts many beneficial insects, so consider leaving some flowers in the garden to provide food and shelter for them.

Here are three common problems you might encounter growing Yarrow in Southern California:

Aggressive Spreading

• What it looks like: Yarrow spreads rapidly via rhizomes (underground stems), quickly filling garden beds and potentially encroaching on other plants.
• What causes it: Our long growing season and mild winters allow Yarrow to thrive and spread aggressively.
• How to fix/prevent it: Plant Yarrow in containers or raised beds to restrict its spread. Divide clumps every 2-3 years to manage its size. Remove unwanted shoots as they appear.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves 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 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.
• 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.

Southern California Specific Challenges: Our hot summers inland can stress Yarrow, making it more susceptible to powdery mildew and aphids. Santa Ana winds can quickly dry out the soil, so monitor moisture levels closely. While Yarrow is drought-tolerant, it still needs adequate water to thrive, especially during periods of extreme heat.

Yarrow makes a great companion plant for many vegetables and herbs in our Southern California gardens. It attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other pests.

Good companions include tomatoes and peppers, as Yarrow helps to repel pests that can damage these crops. Herbs like rosemary and thyme also benefit from Yarrow's pest-repelling properties. Strawberries also thrive near Yarrow, as it improves their overall health and vigor.

Avoid planting Yarrow near plants in the Brassica family (cabbage, broccoli, kale), as it can attract cabbage moths.