Tansy in Zone 7A — Mountain West

Tansy is worth growing in your Zone 7A Mountain West garden for its beautiful foliage and its practical use as a natural insect repellent. The intense sunlight here at altitude really brings out its aromatic oils, making it an effective deterrent against pests in your garden and even inside your home. Plus, the cool nights even in summer seem to intensify its fragrance.

Our short growing season and alkaline soil here in the Mountain West present unique challenges, but Tansy is a tough plant that can thrive with the right approach. With a 173-day growing season, you have plenty of time to get a good harvest if you time your planting correctly.

Starting Tansy indoors isn't always necessary, but it can give you a head start, especially if you're aiming for an early harvest. Begin your seeds indoors from mid February through early March, roughly six weeks before you plan to transplant them outside. Use seed trays with a good seed-starting mix and provide warmth and light.

Bottom watering is a great trick to keep the soil consistently moist without damping off. Remember, spring can be late here, so don't rush to put them out too early.

Transplant your Tansy seedlings outdoors from early April through early May, after the danger of hard frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense sun and cooler nights.

Space the plants 12-18 inches apart to allow for good air circulation and growth. Keep an eye on the weather forecast, as late-season snow or hail can still occur, even in April.

Direct sowing Tansy is a straightforward method that works well in our climate. Sow seeds directly into the garden from early April through mid July. Ensure the soil is well-draining and has warmed up a bit.

Prepare the soil by loosening it and removing any rocks or debris. Space seeds 12-18 inches apart. Direct sowing avoids transplant shock, but you'll need to be diligent about weeding until the seedlings are established.

Tansy is incredibly drought-tolerant, making it a perfect fit for our dry Mountain West climate. Once established, it thrives on neglect. Overwatering or over-fertilizing can actually make it more aggressive.

During the peak of summer, when temperatures can reach 85°F, water deeply about once every two weeks, or when the top two inches of soil feel dry to the touch. Use the "finger test" to check the moisture level. Water at the base of the plant to avoid wetting the foliage, which helps prevent fungal issues in our low-humidity environment.

Signs of underwatering include wilting or drooping leaves, while yellowing leaves can indicate overwatering. A layer of mulch can help retain moisture and regulate soil temperature, which is especially helpful with our intense sun.

Pruning Tansy is mainly about controlling its spread and encouraging continued growth. Deadhead the plants regularly throughout the growing season to prevent aggressive self-seeding. Remove the spent flowers as soon as they start to fade.

In the fall, after the first frost around early October, cut the plants back to the ground. This helps keep the plant tidy and encourages new growth in the spring. Given its vigorous nature, you might need to consider containing it within a raised bed or using barriers to prevent it from spreading too much.

You can expect your first harvest of Tansy starting in mid June and continuing through mid October. Tansy is primarily grown for its insect-repelling properties rather than culinary use, as it can be toxic in large amounts. The button-like yellow flowers that bloom midsummer are a good indicator that the plant is mature and ready to be used.

Harvest the leaves and flowers by snipping them off with scissors or pruning shears. Regular harvesting encourages continued production throughout the season. As the first frost approaches in early October, harvest any remaining foliage and flowers for drying and storage.

Here are two common problems you might encounter with Tansy in the Mountain West:

Invasive Spread

• What it looks like: Tansy spreads aggressively, forming dense clumps and potentially taking over garden beds.
• What causes it: Its vigorous growth habit and prolific self-seeding allow it to quickly colonize new areas.
• How to fix/prevent it: Contain the plant within raised beds or use physical barriers to prevent its roots from spreading. Regularly deadhead the flowers to prevent self-seeding. Be vigilant about removing unwanted seedlings as they appear.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects thrive in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Strong water spray to knock them off. Encourage natural predators like ladybugs and lacewings. Use insecticidal soap for heavy infestations or neem oil for a systemic treatment. Avoid excess nitrogen fertilizer, which attracts them.

Mountain West Specific Challenges: The moderate-at-altitude heat and low humidity of the Mountain West can actually benefit Tansy by reducing the risk of fungal diseases. However, the intense sun can stress the plant if it's not adequately watered, and the alkaline soil may require amendments to ensure optimal growth.

Tansy makes a great companion plant for several vegetables and fruits in your Mountain West garden. It is said to repel certain pests.

• Potato: Tansy can help deter potato beetles, a common pest in our region.
• Squash and Cucumber: Tansy's insect-repelling properties can protect these crops from squash bugs and cucumber beetles.
• Raspberry: Tansy may help deter certain raspberry pests.

Avoid planting Tansy near brassicas (cabbage, broccoli, kale) as it can attract cabbage moths.