Tansy in Zone 8A — Pacific Northwest

Tansy is a striking addition to a Pacific Northwest garden, offering vibrant color and acting as a natural insect repellent. Its fern-like foliage and button-like yellow flowers brighten up any space, and it's incredibly low-maintenance – a perfect fit for our mild summers and cool nights. Plus, it's a favorite for attracting beneficial insects to your garden.

While we might struggle with heat-loving plants, Tansy thrives in our climate. Our 203-day growing season gives you plenty of time to establish it, whether you start indoors or sow directly into the garden.

Starting Tansy indoors in our region is optional, but can give you a head start. If you're eager to get things going, sow seeds indoors from early to late February, about six weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and provide warmth and light – a heat mat and grow lights work well on those overcast spring days. Water from the bottom by setting the tray in a shallow dish of water, allowing the soil to soak it up. This prevents damping-off, which can be a problem with our slow spring starts.

Transplant your Tansy seedlings outdoors in late March through late April, once the danger of hard frost has passed. Before planting, 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. Be mindful of potential late cold snaps that can occur during this period. A layer of horticultural fleece can protect your young plants if needed.

Direct sowing Tansy is a simple and effective method, especially in our climate. Sow seeds directly into the garden from late March through early August.

Prepare the soil by loosening it and removing any weeds. Tansy isn't too picky, but well-draining soil is best. Scatter the seeds thinly over the soil surface and gently press them in. Keep the soil consistently moist until the seedlings emerge, then thin them to 12-18 inches apart. Direct sowing can be slower than starting indoors, but it avoids transplant shock.

Tansy is exceptionally drought-tolerant and thrives on neglect, making it a perfect fit for our dry summer months in the Pacific Northwest. In fact, overwatering and over-fertilizing can actually make it more aggressive.

During our wet springs, you likely won't need to water at all. Once the dry summer months arrive, check the soil moisture with the finger test – stick your finger about two inches deep into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week during the driest periods. Watering at the base of the plant is preferable, helping to prevent fungal issues.

Signs of underwatering include wilting or drooping leaves. Overwatering can lead to root rot, indicated by yellowing leaves and a generally unhealthy appearance. Mulching around the base of the plant with compost can help retain moisture and suppress weeds, which is beneficial during our drier summers.

Pruning Tansy is essential to keep it in check, as it can be quite vigorous. The most important task is deadheading, which means removing the spent flowers. Do this regularly throughout the growing season to prevent it from aggressively self-seeding.

In late fall, after the first frost around late October, cut the plant back to the ground. This helps tidy up the garden for winter and encourages new growth in the spring. Since Tansy can spread, consider containing it with barriers to keep it from taking over your garden beds.

You can expect your first harvest of Tansy in early June through early November, about 75 days after planting. The button-like yellow flowers will bloom midsummer, indicating that it's ready to be harvested for its insect-repelling properties.

Harvest by cutting the stems just above a leaf node. This encourages new growth and continued production. Tansy is typically used as an insect repellent and is not for culinary use as it can be toxic in large amounts.

As the first frost approaches in late October, you can still harvest Tansy. Cut and dry the stems to use as insect repellent over the winter.

Here are two common problems you might encounter with Tansy in the Pacific Northwest:

Invasive Nature

• What it looks like: Tansy spreads rapidly, overtaking garden beds and crowding out other plants.
• What causes it: Tansy is a vigorous grower and readily self-seeds. Our mild, wet springs and long growing season provide ideal conditions for its spread.
• How to fix/prevent it: Contain Tansy by planting it in pots or using underground barriers to prevent root spread. Regularly deadhead flowers before they set seed. Remove unwanted seedlings as soon as they appear.

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. Avoid excess nitrogen fertilizer (it attracts them).

Pacific Northwest Specific Challenges: Our mild summers and dry-summer humidity can actually help with Tansy, reducing the risk of fungal diseases that plague other regions. However, our wet springs can encourage rapid growth, making it even more important to manage its spread. Slugs can also be a nuisance for young plants, so use slug bait or other control methods as needed.

Tansy makes a good companion plant for several vegetables and fruits in the Pacific Northwest garden. It is said to repel certain pests.

Good companions include potatoes, squash, and cucumbers. Tansy repels potato beetles and squash bugs, protecting these crops from damage. It also benefits raspberries, deterring raspberry beetles.

Avoid planting Tansy near plants that are sensitive to its allelopathic properties (the release of chemicals that inhibit the growth of other plants), though these effects are not well-documented.