Tansy in Zone 3B — Mountain West

Tansy is a fantastic addition to any Mountain West garden. It's incredibly low-maintenance once established, offering beautiful foliage and cheerful yellow button flowers. Plus, it's a natural insect repellent, which is a huge win in our high-altitude gardens where we often battle pests without wanting to resort to harsh chemicals.

Our short growing season and cool nights here in Zone 3B can be tricky, but Tansy is surprisingly hardy. With a little planning around our 108-day growing season, you can easily enjoy this plant in your garden.

Starting Tansy indoors is an option, but honestly, it's often not necessary in our climate. If you're eager to get a head start, you can sow seeds indoors from late March through mid April, about six weeks before our typical last frost.

Use seed trays with a good seed-starting mix, and provide warmth and plenty of light – a sunny south-facing window or grow lights work well. Water gently from the bottom to avoid damping off. Keep in mind that our late springs here in the Mountain West mean you'll need to be patient and watch the weather before transplanting.

Transplanting Tansy outdoors should happen from mid May through early June, once the risk of hard frost has passed. Before planting, be sure to harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space plants about 12-18 inches apart. Even though our intense sun can be a blessing, be mindful that young transplants need protection from UV shock at first. A row cover can help.

Direct sowing Tansy is a perfectly viable option in our climate, especially if you're aiming for a low-maintenance approach. Sow seeds from mid May through mid June, once the soil has warmed up a bit.

Prepare the soil by loosening it and removing any large clumps or rocks. Lightly cover the seeds with soil. Space them about 12-18 inches apart. Just remember that direct-sown plants might take a little longer to mature than those started indoors.

Tansy thrives on neglect, which is a huge plus for us Mountain gardeners! It's very drought-tolerant once established, so overwatering is a much bigger concern than underwatering.

During the peak of our moderate-at-altitude summer heat, water only when the top two inches of soil feel dry to the touch – use the finger test. Typically, this translates to about ½ inch of water per week, if that. Water at the base of the plant rather than overhead to minimize moisture on the foliage, which helps prevent potential issues in our low-humidity environment.

Signs of underwatering include wilting or drooping leaves, while yellowing leaves can indicate overwatering. Mulching around the base of the plant with gravel or wood chips helps retain moisture and suppress weeds, but be careful not to overdo it, as Tansy prefers drier conditions.

Pruning Tansy is mainly about keeping it in check and preventing it from becoming too aggressive. Deadhead spent flowers throughout the growing season to prevent self-seeding. Simply snip off the flower heads as they fade.

Toward the end of the season, after our first frost around early September, cut the plant back to the ground. This encourages new growth in the spring and helps maintain its shape. Remember, Tansy is vigorous, so don't be afraid to prune it back hard if it starts to spread too much.

You can expect your first harvest of Tansy from late July through mid September, about 75 days after planting. The plant is ready for harvest when the button-like yellow flowers are in full bloom.

Harvest by cutting the stems with sharp scissors or pruning shears. Be sure to leave enough foliage on the plant to allow it to continue producing. Tansy is primarily used as an insect repellent, so hang the stems to dry in a cool, dark place.

As our first frost approaches in early September, you can harvest the remaining foliage and dry it for winter use. Remember that Tansy is not for culinary use and can be toxic if ingested in large amounts.

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

Invasive Spread

• What it looks like: Tansy spreads aggressively, sending out runners and self-seeding readily. You'll find it popping up in areas where you didn't plant it.
• What causes it: Tansy is just naturally vigorous, and our intense sun helps it thrive. It's not particularly picky about soil, either, so it can establish itself easily.
• How to fix/prevent it: Plant Tansy in a contained area, like a raised bed or surrounded by edging that goes at least 12 inches into the ground. Deadhead flowers regularly to prevent self-seeding. Be vigilant about removing any unwanted seedlings.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. You might also see a sticky honeydew residue and curled or distorted new growth.
• What causes it: Aphids are rapid-reproducing sap-sucking insects that love warm weather. In the Mountain West, our temperature swings can cause aphid populations to explode unexpectedly.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage natural predators like ladybugs. Insecticidal soap or neem oil works well for heavy infestations. Avoid over-fertilizing with nitrogen, as that attracts them.

Mountain West Specific Challenges: Our moderate-at-altitude summer heat, low humidity, and dry rainfall generally benefit Tansy, making it less prone to fungal diseases. However, the intense sun can stress young plants, so provide some initial shade. Keep an eye out for aphids, as our fluctuating temperatures can lead to sudden outbreaks.

Tansy makes a great companion plant for several vegetables and fruits in our Mountain gardens.

• Potato: Tansy repels potato beetles, a common pest in our area.
• Squash: Tansy helps deter squash bugs and vine borers.
• Cucumber: Tansy repels cucumber beetles.
• Raspberry: Tansy helps to deter certain raspberry pests.

Avoid planting Tansy near cabbage or other brassicas, as it can attract cabbage moths.