Tansy in Zone 7B — Northern California

Tansy is a rewarding addition to any Northern California garden. Its fern-like foliage and bright yellow flowers not only add visual appeal but also serve as a natural insect repellent. Plus, it's incredibly low-maintenance, making it perfect for our busy lifestyles and water-wise gardening practices.

Even with our dry summers and occasional water restrictions, Tansy thrives in our Mediterranean climate. Our long growing season, stretching nearly 245 days from mid-March to mid-November, gives you plenty of time to establish and enjoy this resilient herb.

Starting Tansy indoors isn't essential in our mild climate, but it can give you a head start. If you choose this route, begin sowing seeds indoors from mid January through early February, about six weeks before you plan to transplant them outdoors.

Use seed trays filled with a well-draining seed-starting mix, keep them consistently moist (bottom watering is great for this!), and provide a warm location with plenty of light. A sunny windowsill or grow lights will work well. Given our early springs, this can give you larger plants ready to go as soon as the soil warms up.

Transplant your Tansy seedlings outdoors in early to late March once the danger of frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Choose a sunny or partially shaded location and space the plants 12-18 inches apart. Keep an eye on the weather forecast during this time – a late cold snap is always possible in Northern California, and you might need to cover your young plants if temperatures dip unexpectedly.

Direct sowing Tansy is a simple and effective method, especially if you're looking for a low-fuss approach. Sow seeds directly into the garden from early March through mid August.

Prepare the soil by loosening it and removing any weeds. Lightly press the seeds into the soil surface – they need light to germinate. Keep the soil consistently moist until seedlings emerge. Thin seedlings to 12-18 inches apart once they are a few inches tall.

Tansy is exceptionally drought-tolerant, making it an ideal choice for Northern California gardens where water conservation is crucial. Once established, it thrives on minimal watering.

During our hot, dry summers, water deeply but infrequently – about once every 2-3 weeks, or when the top 2 inches of soil feel dry to the touch ("the finger test"). Aim for about 1 inch of water per week, either from rainfall or irrigation. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our low-humidity environment.

Signs of underwatering include wilting or drooping leaves. Overwatering, on the other hand, can lead to root rot and a generally unhappy plant. A layer of mulch around the base of the plant will help retain moisture and suppress weeds, further reducing the need for frequent watering.

Regular deadheading is essential to prevent Tansy from aggressively self-seeding, a common concern in our region. Remove spent flowers throughout the growing season to encourage continued blooming and keep the plant tidy.

In late fall, after the first frost around mid- November, cut the plant back to the ground. This will help it conserve energy over the winter and promote vigorous growth in the spring. Because Tansy can be so vigorous, you may need to consider containing it by planting it in a pot or using underground barriers to prevent it from spreading.

You can expect your first harvest of Tansy from mid May through late November, about 75 days after planting. The button-like yellow flowers bloom in midsummer, signaling that the plant is ready for harvest.

Harvest by cutting stems as needed, being careful not to damage the rest of the plant. While Tansy is traditionally used as an insect repellent, it's important to remember that it's not for culinary use and can be toxic in large amounts. Continue harvesting throughout the growing season to encourage new growth. As the first frost approaches in mid- November, you can harvest any remaining foliage for drying and use as an insect repellent indoors.

Here are two common problems you might encounter with Tansy in Northern California:

Invasive Tendencies

• What it looks like: Tansy spreads rapidly, popping up in unwanted areas of your garden.
• What causes it: Tansy is a vigorous grower and readily self-seeds, especially in our long growing season.
• How to fix/prevent it: Plant Tansy in a container or use underground barriers to contain its roots. Deadhead spent flowers regularly to prevent seed production. Be vigilant about removing any unwanted seedlings.

Aphids

• What it looks like: Clusters of tiny insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Aphids are attracted to new growth and can thrive in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Knock aphids off with a strong spray of water. Encourage natural predators like ladybugs and lacewings. Use insecticidal soap for heavy infestations or neem oil for a systemic treatment. Avoid excessive nitrogen fertilizer, which can attract aphids.

Northern California Specific Challenges: Our moderate-to-hot summers can stress Tansy if it's not properly watered, making it more susceptible to pests. However, our dry summers generally help prevent fungal diseases. Be sure to provide adequate water without overwatering, and monitor your plants regularly for any signs of problems.

Tansy makes a good companion plant for several vegetables and herbs in the Northern California garden. It's known to repel certain insects, benefiting plants like:

• Potatoes: Tansy can help deter potato beetles, a common pest in our region.
• Squash and Cucumber: Tansy can help repel squash bugs and cucumber beetles.
• Raspberries: Tansy is believed to deter raspberry beetles and other pests that can damage the fruit.

Avoid planting Tansy near brassicas (cabbage, broccoli, kale), as it may inhibit their growth.