Yarrow in Zone 10B — Southern California

Yarrow is a fantastic addition to any Southern California garden. Its feathery foliage and clusters of blooms add beauty, attract beneficial insects, and can even be dried for long-lasting arrangements. Plus, it's incredibly water-wise, a definite plus given our ongoing drought conditions.

While we face challenges like water restrictions and the occasional heat wave inland, yarrow's adaptability and our long growing season (nearly year-round!) make it a reliable and rewarding plant to grow here. You can pretty much always find a time to get it going.

Starting yarrow indoors is an option, especially if you want a head start on blooms. Sow seeds late October through mid November, about 8 weeks before you'd like to transplant. Use seed trays with a good seed-starting mix and keep them consistently moist, bottom watering works great to avoid disturbing the tiny seeds.

Provide warmth and plenty of light, a grow light works well. Remember, our spring comes early here, so starting indoors lets you get a jump on the season.

Transplant your yarrow seedlings outdoors late December through late January. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents transplant shock when they go into the ground.

Space the plants about 12-18 inches apart to allow for their clumping growth habit. Even though our winters are mild, watch out for unexpected cold snaps. If you're after flowers the first year, you might want to buy established starts from your local nursery.

Direct sowing yarrow is a straightforward method that works well in our climate. Sow seeds early January through mid October, giving you a wide window of opportunity. Choose a sunny spot with well-draining soil.

Lightly rake the soil surface and scatter the seeds, gently pressing them in. Keep the soil consistently moist until germination. Remember to thin the seedlings to 12-18 inches apart as they grow.

Yarrow thrives on neglect once it's established, making it perfect for our water-conscious Southern California gardens. During our mild winters, rainfall is often sufficient, so supplemental watering is rarely needed unless we're in a dry spell.

During the hotter summer months, water deeply but infrequently, only when the top 2 inches of soil feel dry to the touch – use the finger test! Aim for about 1 inch of water per week, delivered at the base of the plant to avoid wetting the foliage, which can encourage fungal problems in our moderate humidity.

Overwatering will lead to floppy growth and potentially root rot, so err on the side of dryness. Yellowing leaves can indicate overwatering, while wilting suggests underwatering. Mulching around the base of the plant with organic matter helps retain moisture and suppress weeds, important during our dry summers.

Deadheading is key to keeping your yarrow blooming throughout the season. Snip off spent flowers as soon as they fade to encourage a second flush of blooms. This also prevents the plant from self-seeding too aggressively.

In late fall, after the first frost (usually around late December here), cut the plant back to its basal foliage. Yarrow can be an enthusiastic spreader, so divide the clumps every 2-3 years to keep it in check.

You can expect your first yarrow harvest starting in mid March through early January, about 65 days after planting. Harvest the flowers for drying when they are fully open and the colors are vibrant. Cut the stems just above a leaf node.

Hang the harvested flowers upside down in a cool, dark, and dry place to dry them thoroughly. Regular harvesting encourages continued production throughout the growing season. Even as our mild winter approaches, yarrow can still provide blooms if you've kept it well-maintained.

Yarrow is generally low-maintenance, but here are a few common problems to watch out for in Southern California:

Aggressive Spreading

• What it looks like: Yarrow pops up in unwanted areas of your garden, spreading beyond its intended space.
• What causes it: Yarrow spreads via rhizomes (underground stems) and seeds, and it can be quite vigorous in our long growing season.
• How to fix/prevent it: Plant yarrow in containers or use edging to contain its spread. Regularly divide clumps every few years to manage its growth. Remove unwanted seedlings promptly.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems. Leaves curl, yellow, and die.
• What causes it: Fungal disease favored by warm days, cool nights, and moderate humidity – conditions common in our coastal areas. 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) can be 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, which we have plenty of here. 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: The combination of summer heat inland and low-to-moderate humidity can stress yarrow, making it more susceptible to powdery mildew. Santa Ana winds can also dry out the plants quickly, so be sure to monitor soil moisture during these periods.

Yarrow is a great companion plant for many vegetables and herbs in your Southern California garden.

• Tomato and Pepper: Yarrow attracts beneficial insects like ladybugs and hoverflies, which prey on aphids and other pests that can damage tomatoes and peppers.
• Herbs: Planting yarrow near herbs like rosemary and thyme can enhance their essential oil production and attract pollinators.
• Strawberry: Yarrow is said to improve the flavor of strawberries and deter pests.

Avoid planting yarrow near plants that prefer consistently moist soil, as yarrow thrives in drier conditions.