Tansy in Zone 8B — Pacific Northwest

Tansy is worth growing in your Pacific Northwest garden for its striking foliage and sunny yellow flowers. It's a low-maintenance plant that's surprisingly versatile as a natural insect repellent. Plus, it thrives in our mild summers and cool nights, adding a touch of wild beauty to your garden.

While our wet springs and the risk of late blight can be concerns, Tansy is a hardy plant that can handle these challenges with proper timing and care. Our long, 210-day growing season gives you plenty of time to enjoy its benefits.

Starting Tansy indoors in the PNW is optional, but it can give you a head start, especially if you want earlier blooms. Begin in early to late February, about six weeks before you plan to transplant.

Use seed trays filled with a good seed-starting mix, and keep them warm and consistently moist. Bottom watering helps prevent damping-off, which can be a problem during our overcast spring days. Provide supplemental light, as our natural light levels are still low at this time of year.

Transplant your Tansy seedlings outdoors in late March through mid April, once the soil has warmed up a bit. Before transplanting, harden off the seedlings by gradually exposing them to outdoor conditions for about a week.

Space them 12-18 inches apart to allow for their clumping growth habit. Keep an eye on the weather forecast, as we can still get unexpected cold snaps during this time. Protect young plants if necessary.

Direct sowing Tansy is a straightforward option in our region. Sow seeds outdoors from late March through early August.

Prepare the soil by loosening it and removing any weeds. Tansy isn't picky about soil, but well-draining soil is best. Sow seeds shallowly and keep the soil consistently moist until germination. Thin seedlings to 12-18 inches apart. Direct sowing is easy but you need to remember to water regularly until the seedlings have established.

Tansy is very drought-tolerant and thrives on neglect, making it a great choice for our dry summer months in the Pacific Northwest. Overwatering is a bigger concern than underwatering.

During our wet springs, you likely won't need to water at all. Once the dry summer months arrive, check the soil moisture before watering. Stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week, especially during the hottest parts of the summer (which are still quite mild here).

Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our sometimes humid conditions. Yellowing leaves can be a sign of overwatering, while wilting leaves indicate underwatering. A layer of mulch, like wood chips, can help retain moisture and suppress weeds.

Pruning Tansy is mainly about managing its spread and encouraging continued growth. Deadhead spent flowers regularly throughout the growing season to prevent aggressive self-seeding.

Simply snip off the faded flower heads with pruners or scissors. In the fall, after the first frost around early November, cut the plant back to the ground. This helps to tidy up the garden and prepare the plant for winter dormancy.

You can expect your first harvest of Tansy around early June, about 75 days after planting, and continue harvesting through early November. Tansy is primarily used for its insect-repellent properties, not for culinary purposes, so you're harvesting for the foliage and flowers.

Look for the button-like yellow flowers that bloom in midsummer. To harvest, simply cut the stems with pruners or scissors. Regular harvesting can encourage continued production of new growth. As the first frost approaches in early November, you can harvest the remaining foliage and flowers for drying or other uses.

Here are a couple of common problems you might encounter with Tansy in the Pacific Northwest:

Invasive Spread

• What it looks like: Tansy spreads rapidly, forming dense clumps and potentially crowding out other plants in your garden.
• What causes it: Tansy is a vigorous grower and readily self-seeds, especially in our mild climate.
• How to fix/prevent it: Contain Tansy by planting it in a raised bed or using underground barriers to prevent its roots from spreading. Deadhead spent flowers to reduce self-seeding.

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: Rapid-reproducing sap-sucking insects. Populations explode in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage beneficial insects like ladybugs and lacewings. Insecticidal soap can be used for heavy infestations. Avoid over-fertilizing, as excess nitrogen attracts aphids.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer rainfall generally benefit Tansy, as it prefers drier conditions and isn't prone to many heat-related issues. However, the dry-summer humidity can still create conditions for fungal diseases if the plants are overcrowded, so ensure good air circulation.

Tansy makes a good companion plant for several vegetables in the Pacific Northwest garden. It repels certain pests, benefiting plants like potatoes, squash, and cucumbers. It also helps protect raspberries from certain insects. Avoid planting Tansy near brassicas like cabbage and broccoli, as it can inhibit their growth.