Yarrow in Zone 8A — Northern California

Yarrow is a fantastic addition to any Northern California garden. Its cheerful flowers bring a splash of color and attract beneficial insects like crazy, which is a big win. Plus, it's super drought-tolerant, perfect for our dry summers, and the blooms make beautiful dried arrangements.

We all know gardening in NorCal comes with its own set of challenges, from water restrictions to the occasional fire season. Luckily, Yarrow is pretty forgiving, and our long 255-day growing season gives you plenty of time to get it established and enjoy its benefits.

Starting Yarrow indoors isn't strictly necessary, but it can give you a head start, especially if you're aiming for blooms in the first year. If you want to go this route, sow your seeds indoors from late December through mid January, about eight weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and keep them in a warm spot with plenty of light. Bottom watering is your friend here – set the tray in a shallow dish of water and let the soil soak it up. Since spring comes early in our region, you'll want to get a jump start if you want those first-year blooms.

Transplanting Yarrow outdoors is best done from late February through late March. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Choose a sunny spot with well-drained soil and space your plants 12-18 inches apart. While late February and March are generally mild, keep an eye on the forecast for any late frosts, which can happen. Buying starts can guarantee flowers the first year, since the plant will be mature.

Direct sowing Yarrow is a simple and reliable method, especially if you're not in a rush for blooms. Sow seeds directly into the garden from early March through early September. Yarrow seeds need light to germinate, so don't bury them too deeply.

Prepare the soil by loosening it and removing any weeds. Keep the soil consistently moist until the seedlings emerge. Thin the seedlings to 12-18 inches apart once they're a few inches tall. Direct sowing is a great low-fuss option, but remember you'll probably have to wait until the second year for significant flowering.

Yarrow is a champ when it comes to drought tolerance, which makes it a perfect plant for Northern California gardens facing water restrictions. Once established, it needs very little supplemental watering. The key is to avoid overwatering, which can lead to floppy growth and other problems.

During our dry summers, water deeply but infrequently. A good rule of thumb is to check the soil with your finger – if the top two inches are dry, it's time to water. Aim for about an inch of water per week during the hottest months. Water at the base of the plant to avoid wetting the foliage, which helps prevent fungal diseases in our low-humidity environment.

In spring and fall, rainfall might be enough to keep your Yarrow happy. Keep an eye out for signs of underwatering, like wilting leaves, or overwatering, like yellowing leaves and soggy soil. A layer of mulch around the base of the plant will help retain moisture and keep the soil cool during the summer heat.

Pruning Yarrow is pretty straightforward and helps keep it looking its best. Deadhead spent flowers regularly throughout the growing season to encourage more blooms. Simply snip off the flower heads just below the lowest set of petals.

In late fall, after the first frost around mid- November, cut the plant back to its basal foliage (the leaves at the base of the plant). Yarrow can be a bit aggressive, so divide the clumps every 2-3 years to keep it under control and rejuvenate the plant.

You can expect your first Yarrow harvest starting in mid May and continuing through late November in our Northern California climate. The flowers are ready to harvest when they are fully open and the petals are vibrant. 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 drying, hang the stems upside down in a cool, dark, and dry place. Even as the first frost approaches in mid- November, you can often still harvest some late blooms for drying.

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 popping up in unwanted areas of your garden.
• What causes it: Its rhizomatous roots can spread quickly, especially in well-draining soil.
• How to fix/prevent it: Plant in containers or use barriers to contain the roots. Regularly divide the plant to control its spread.

Powdery Mildew:

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves may 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 by spacing plants adequately and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays can help. A milk spray (1 part milk to 9 parts water) is surprisingly effective.

Aphids:

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects. Populations explode in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Strong water spray to knock them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap for heavy infestations. Avoid excess nitrogen fertilizer.

Northern California Specific Challenges: Our moderate-to-hot summers and dry conditions can stress Yarrow if it's not properly established. While it's drought-tolerant, young plants need regular watering until they are established. Also, be mindful of fire season and keep the area around your plants clear of dry debris.

Yarrow is a wonderful companion plant in the Northern California garden. It attracts beneficial insects that help control pests on other plants.

Good companions include:

• Tomatoes: Yarrow attracts hoverflies, which prey on tomato hornworms.
• Peppers: Similar to tomatoes, Yarrow helps attract beneficial insects that protect peppers.
• Herbs: Many herbs, like rosemary and thyme, benefit from the pest control Yarrow provides.
• Strawberries: Yarrow can help improve the overall health and vigor of strawberry plants.

I wouldn't suggest planting it with anything that needs a lot of water, since Yarrow prefers drier conditions.