Tansy in Zone 5B — Mountain West

Tansy is a hardy perennial that thrives in our Mountain West gardens, offering more than just visual appeal. Its aromatic foliage makes it a valuable addition for natural pest control. Plus, its vigorous growth habit means you'll have plenty to share!

Our short growing season and intense sun can be a challenge, but Tansy is well-suited to handle them. With a 149-day growing season, you have plenty of time to get a good harvest, whether you start seeds indoors or direct sow.

Starting Tansy indoors is an option, especially if you want a head start on our short growing season, but it's not strictly necessary. If you choose to go this route, start your seeds indoors from early to late March, about 6 weeks before you plan to transplant them outside.

Use seed trays with a good seed-starting mix, and keep them in a warm location with plenty of light. Bottom watering is a great technique to avoid damping off, especially when our spring weather is still unpredictable. Remember, our late springs mean you'll want to keep an eye on the weather before transplanting.

Transplant your Tansy seedlings outdoors from late April through mid May, once the danger of hard frost has passed. Be sure to harden off your seedlings for about a week before transplanting. Gradually expose them to the outdoor elements to prevent shock.

Space your plants 12-18 inches apart in well-draining soil. Keep an eye on the weather forecast – late spring snow or hail is always a possibility here in the mountains!

Direct sowing Tansy is a straightforward method that works well in our climate, as Tansy is quite hardy. Sow seeds directly into the garden from late April through early July. Direct sowing gives you a wider window.

Prepare the soil by loosening it and removing any large clumps or rocks. Sow seeds about ¼ inch deep, and space them 12-18 inches apart. Keep the soil consistently moist until the seedlings emerge.

Tansy is remarkably drought-tolerant, which is a huge plus in our dry Mountain West climate. It actually thrives on neglect, so avoid overwatering, which can make it overly aggressive.

During the active growing season, water deeply but infrequently. A good rule of thumb is to check the soil about 2 inches deep – if it's dry, it's time to water. In our dry climate, an inch of water per week is usually sufficient, especially as mature plants become established. Focus watering at the base of the plant to avoid wetting the foliage, which helps prevent any potential fungal issues in our low-humidity environment.

Signs of underwatering include wilting leaves, while yellowing leaves can indicate overwatering. Mulching around the base of the plants with a layer of organic matter like straw or wood chips helps retain moisture and regulate soil temperature, which can be crucial with our intense sun.

Deadheading is key to maintaining Tansy and preventing it from becoming overly aggressive. Remove the spent flower heads as they fade throughout the growing season. This will prevent self-seeding, which can quickly lead to Tansy spreading where you don't want it.

In late fall, after the first frost around early October, cut back the entire plant to ground level. This will help tidy up the garden and encourage fresh growth in the spring. Given its vigorous nature, consider planting Tansy in a contained area or using barriers to prevent it from spreading beyond its designated space.

You can expect your first harvest of Tansy from early July through early October, about 75 days after planting. The plant is ready for harvest when the button-like yellow flowers bloom midsummer.

To harvest, simply cut the stems with foliage as needed. Remember that Tansy is primarily used as an insect repellent and is not recommended for culinary use due to potential toxicity in large amounts. Regular harvesting encourages continued production throughout the season.

As the first frost approaches in early October, you can harvest the remaining foliage for drying and future use.

Tansy is generally a low-maintenance plant, but there are a couple of common issues to watch out for in our Mountain West gardens: invasiveness and aphids.

Invasiveness

• What it looks like: Tansy spreading rapidly beyond its intended planting area, potentially crowding out other plants.
• What causes it: Tansy is a vigorous grower and readily self-seeds. This is especially pronounced with our intense summer sun.
• How to fix/prevent it: Plant Tansy in a contained area or use physical barriers to prevent its roots from spreading. Deadhead flowers regularly to prevent seed production. Be vigilant about removing any unwanted seedlings.

Aphids

• What it looks like: Clusters of tiny (green, black, or white) insects on stems and undersides of leaves. You might also notice a sticky residue (honeydew) or curled/distorted new growth.
• What causes it: Aphids are sap-sucking insects that thrive in warm weather. They can multiply quickly, especially if ants are present (ants protect them for honeydew).
• How to fix/prevent it: A strong spray of water can knock aphids off the plants. Encourage natural predators like ladybugs and lacewings. For heavy infestations, use insecticidal soap or neem oil. Avoid over-fertilizing with nitrogen, which can attract aphids.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity generally favor Tansy, reducing the risk of fungal diseases. However, the intense sun can exacerbate aphid problems, as they reproduce more quickly. Regular monitoring and prompt action are key to keeping your Tansy healthy and contained.

Tansy makes a great companion plant for several garden vegetables in the Mountain West. It's known to repel certain pests, benefiting plants nearby.

Good companions include potatoes, squash, cucumbers, and raspberries. Tansy helps deter potato beetles and squash bugs, protecting these crops. Its pest-repelling properties can also reduce insect pressure on cucumbers and raspberries. Avoid planting Tansy near brassicas like cabbage or broccoli, as it can inhibit their growth.