Yarrow in Zone 8B — Northern California

Yarrow is a fantastic addition to any Northern California garden. Its delicate, feathery foliage and clusters of colorful blooms bring beauty, attract beneficial insects, and even offer medicinal properties. Plus, it's incredibly drought-tolerant, a real asset in our Mediterranean climate.

We know our region presents challenges with dry summers and the occasional water restriction, but Yarrow is well-suited to handle them. With our long, 269-day growing season, you'll have plenty of time to enjoy its blooms. Careful planning and attention to watering will set you up for success.

Starting Yarrow indoors isn't essential in our climate, but it can give you a head start, especially if you want blooms in the first year from seed. If you choose to go this route, aim to sow seeds from mid December through early January, about eight weeks before you'd like to transplant them outdoors.

Use seed trays with a well-draining seed-starting mix. Keep the soil consistently moist (bottom watering is a great technique to avoid disturbing the tiny seeds) and provide warmth and bright light, either from a sunny window or a grow light. Given our early spring character, getting a jump start indoors can be worthwhile.

Transplanting Yarrow outdoors can be done from mid February through mid March. Before you plant, be sure to harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Plant them 12-18 inches apart in a sunny spot with well-drained soil. Keep an eye on the weather forecast, as we can still get some late frosts during this time. If you're looking for flowers the first year, consider buying starts from a local nursery instead of growing from seed. Yarrow is a perennial, so it will come back year after year.

Direct sowing Yarrow is a simple and reliable method in our climate, thanks to our long growing season. Sow seeds from early March through early September, ensuring the soil temperature is consistently above 60°F.

Prepare the soil by loosening it and removing any weeds. Sprinkle the seeds lightly on the surface and gently press them into the soil. Keep the soil consistently moist until the seedlings emerge. Thin the seedlings to 12-18 inches apart once they are a few inches tall.

Yarrow thrives on neglect, making it perfect for water-wise gardening in Northern California. Once established, it's very drought-tolerant, a huge plus during our dry summers. Overwatering is a bigger concern than underwatering, as it can lead to floppy growth.

During the spring, water deeply about once a week, providing about 1 inch of water. Use the "finger test" – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. In the heat of summer, you might need to water every 5-7 days, especially for younger plants. Established plants can often go much longer without supplemental water. Water at the base of the plant to avoid wetting the foliage, given our low humidity.

Yellowing leaves can indicate overwatering, while wilting can signal underwatering. A layer of mulch around the base of the plant will help retain moisture in the soil and suppress weeds, but avoid piling it up against the stem.

Deadheading is key to keeping your Yarrow blooming throughout the season. Simply snip off the spent flower heads just below the flower, encouraging the plant to produce more blooms.

In late fall, after the first frost around late November, cut the plant back to its basal foliage (the leaves at the base of the plant). This helps tidy up the garden and prepares the plant for winter dormancy. Because Yarrow can be aggressive, divide the clumps every 2-3 years to keep it under control.

You can expect your first harvest of Yarrow flowers from early May through early December, depending on when you planted. The flowers are ready to harvest when they are fully open and the colors are vibrant.

Cut the stems at the base of the flower head, being careful not to damage the surrounding foliage. For drying, hang the stems upside down in a cool, dark, and dry place until they are completely dry. Regularly harvesting the flowers will encourage the plant to produce more blooms throughout the season. Even as the first frost approaches in late November, 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 Northern California:

Spreads Aggressively

• What it looks like: Yarrow can quickly spread via rhizomes (underground stems), popping up in unwanted areas of your garden.
• What causes it: Our long growing season allows Yarrow ample time to spread. It thrives in our climate and can become invasive if not managed.
• How to fix/prevent it: Plant Yarrow in a contained area or raised bed. Regularly dig up and remove any unwanted shoots. Divide the plant every 2-3 years to control its size.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems, and sometimes flower heads. Leaves may curl, yellow, and eventually die.
• What causes it: Powdery mildew thrives in warm days, cool nights, and moderate humidity – conditions we sometimes experience in our spring and fall. Dry leaf surfaces actually favor it.
• How to fix/prevent it: Improve air circulation by spacing plants adequately and pruning to open up the canopy. Remove and dispose of affected leaves. Spray with neem oil or potassium bicarbonate. A milk spray (1 part milk to 9 parts water) can also 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: Aphids are sap-sucking insects that reproduce rapidly, especially in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Knock aphids off plants with a strong spray of water. Encourage natural predators like ladybugs and lacewings. Use insecticidal soap for heavy infestations. Neem oil also works well.

Northern California Specific Challenges: While Yarrow is drought-tolerant, extended periods of moderate-to-hot heat during our dry summers can stress the plant, making it more susceptible to pests and diseases. Ensure adequate watering during these periods, especially for younger plants. Pay close attention to watering needs during water restrictions.

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

Good companions:

• Tomatoes and Peppers: Yarrow attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other pests that can damage tomatoes and peppers.
• Herbs: Yarrow's strong scent can deter some pests from attacking herbs like rosemary and thyme.
• Strawberries: Yarrow is said to improve the flavor and vigor of strawberries.

Bad companions:

• Avoid planting Yarrow near plants that prefer very rich, moist soil, as Yarrow thrives in drier conditions.