Tansy in Zone 7B — Pacific Northwest

Tansy is a fantastic addition to any Pacific Northwest garden. Its strong, camphor-like scent makes it a useful insect repellent. Plus, the bright yellow button flowers add a cheerful touch to your garden through the late summer and fall.

While we sometimes struggle to get enough heat for heat-loving plants, Tansy thrives in our mild summers and cool nights. Our long 193-day growing season gives you plenty of time to enjoy this hardy perennial.

Starting Tansy indoors isn't essential, but it can give you a head start, especially if you're aiming for earlier blooms. Sow seeds indoors from mid-February through early March, about six weeks before you plan to transplant. Use seed trays with a good seed-starting mix, keep them consistently moist with bottom watering, and provide a warm location with plenty of light. Remember our overcast spring days can slow growth, so a grow light might be beneficial.

Transplant your Tansy seedlings outdoors from early to late April, once the risk of hard frost has passed. Be sure to harden them off for about a week before planting. Gradually expose them to outdoor conditions, starting with a few hours a day, to help them adjust. Space them 12-18 inches apart in well-drained soil. Be prepared for some cool, wet weather during this time, as April can be unpredictable.

Direct sowing Tansy is a simple and effective method, as the plant is quite hardy. Sow seeds directly into your garden beds from early April through late July. Prepare the soil by loosening it and removing any weeds. Simply scatter the seeds 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.

Tansy is incredibly drought-tolerant, which makes it perfect for our dry summer months in the Pacific Northwest. Once established, it thrives on neglect. In the spring, with our frequent rainfall, you likely won't need to water at all.

During our mild summer months, check the soil moisture with the finger test. Stick your finger about two inches deep into the soil near the base of the plant. If it feels dry, it's time to water. Aim for about an inch of water per week during the driest periods. Water at the base of the plant rather than overhead to avoid potential fungal issues, though our dry summers make this less of a concern than in other regions.

Signs of underwatering include wilted or droopy leaves. Overwatering, though less common, can lead to yellowing leaves and potentially root rot. A layer of mulch around the base of the plant can help retain moisture and suppress weeds, but avoid piling it up against the stem.

Pruning Tansy is primarily about managing its growth and preventing it from becoming too aggressive. Deadhead spent flowers regularly throughout the growing season to prevent self-seeding. Simply snip off the flower heads as they begin to fade.

In late fall, after the first frost around late October, cut the plant back to the ground. This will help tidy up the garden and encourage fresh growth in the spring. Given its vigorous nature, you might also need to contain it with barriers if you don't want it spreading.

You can begin harvesting Tansy for its insect-repellent properties from mid-June through early November, about 75 days after planting. The best time to harvest is when the button-like yellow flowers are in full bloom, typically midsummer.

To harvest, simply cut the stems with flowers using sharp scissors or pruners. Handle the plant with care and be sure to only use it for non-culinary purposes due to its toxicity. Harvest regularly to encourage continued production throughout the season. Even as the first frost approaches in late October, you can still harvest the foliage for use.

Tansy is generally a low-maintenance plant, but here are a couple of potential problems you might encounter in the Pacific Northwest:

Invasive Nature:

• What it looks like: Tansy spreads aggressively, quickly taking over garden beds and crowding out other plants.
• What causes it: Tansy is a vigorous grower and prolific self-seeder. Our mild climate and long growing season allow it to thrive.
• How to fix/prevent it: Contain Tansy by planting it in pots or using underground barriers. Deadhead spent flowers regularly to prevent seed dispersal. Be vigilant about removing unwanted seedlings.

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 attracted to new growth and can multiply rapidly, especially during warm spells.
• How to fix/prevent it: Knock them off with a strong spray of water. Encourage natural predators like ladybugs. Use insecticidal soap or neem oil for heavy infestations.

Pacific Northwest Specific Challenges: Our mild summers and dry-summer rainfall actually benefit Tansy, making it less susceptible to many common plant diseases. The biggest challenge is managing its aggressive growth, as our long growing season allows it to spread quickly.

Tansy makes a good companion plant for several vegetables and fruits in the Pacific Northwest garden. It's said to repel certain pests, benefiting:

• Potatoes: Tansy may help deter potato beetles.
• Squash and Cucumber: Tansy is thought to repel squash bugs and cucumber beetles.
• Raspberries: Tansy may help deter certain raspberry pests.

Avoid planting Tansy near brassicas like cabbage and broccoli, as it can attract cabbage moths.