Tansy in Zone 8A — Desert Southwest

Tansy is a great addition to your Desert Southwest garden for its insect-repelling properties, especially around vegetable plants. It's satisfying to grow something that can naturally help keep pests at bay, and its drought tolerance makes it a perfect fit for our arid climate.

Don't let our extreme heat scare you off. Tansy can handle our long growing season, and by following the planting windows, you'll have no problem getting it established. With a 265-day growing season, you've got plenty of time to make it work!

Starting Tansy indoors in the Desert Southwest gives you a head start, but it's not essential. If you want to get a jump on the season, aim to sow your seeds indoors in early to late January, about six weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and keep them in a warm spot with plenty of light – a sunny windowsill or under grow lights. Bottom watering is your friend here: set the tray in a shallow dish of water and let the soil soak it up to avoid disturbing the tiny seeds. Given our very-early spring character, starting indoors gives you more control.

Transplanting Tansy outdoors in the Desert Southwest should be done in mid February through mid March. Before you put them in the ground, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space your Tansy plants 12-18 inches apart to give them room to spread. Keep an eye on the weather forecast – late cold snaps can happen, even here. A little protection with a frost cloth might be needed if temperatures dip unexpectedly.

Direct sowing Tansy is definitely an option for us Desert Southwest gardeners. You can sow seeds directly into the ground from mid February through late August.

Make sure the soil is well-draining, as Tansy doesn't like soggy feet. Sprinkle the seeds lightly on the surface and gently press them into the soil. Keep the soil consistently moist until the seedlings emerge. Thin them to 12-18 inches apart once they're a few inches tall.

Tansy is incredibly drought-tolerant, which is a huge plus for Desert Southwest gardening. Once established, it practically thrives on neglect. Overwatering is a bigger concern than underwatering with this plant.

During our milder spring and fall, water deeply but infrequently – maybe once every 1-2 weeks, depending on rainfall. In the extreme heat of summer, you might need to water once a week, but always check the soil first. Stick your finger about 2 inches deep; if it's still moist, hold off on watering. Tansy needs very little monsoon moisture.

Aim for about 1 inch of water per week when you do water. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our arid climate. Yellowing leaves are a sign of overwatering, while wilting leaves indicate underwatering. A good layer of rock mulch helps retain moisture and keeps the soil cooler.

Pruning Tansy is all about keeping it in check and encouraging continued growth. Deadhead spent flowers regularly throughout the growing season to prevent it from aggressively self-seeding.

Simply snip off the faded flower heads just below the bloom. In the late fall, after the first frost around late November, cut the plant back to the ground. This will help it overwinter and come back strong in the spring. Given how vigorous it is, consider containing it in a raised bed or pot to prevent it from taking over your garden.

You can expect your first harvest of Tansy from early May through early December, about 75 days after planting. Look for the button-like yellow flowers that bloom in midsummer as an indicator that the plant is mature.

Harvest the leaves and flowers as needed for their insect-repelling properties. Simply snip off the stems with clean pruners. Regular harvesting encourages more growth. As the first frost approaches in late November, you can harvest the remaining foliage and flowers to dry for winter use.

Here are two common problems you might encounter with Tansy in the Desert Southwest:

Invasive Growth

• What it looks like: Tansy spreads rapidly via rhizomes and seeds, popping up in unwanted areas of your garden.
• What causes it: Tansy is a vigorous grower and can quickly become invasive, especially in our long growing season.
• How to fix/prevent it: Contain Tansy by planting it in raised beds or pots. Deadhead flowers before they go to seed. Regularly monitor your garden and remove any unwanted seedlings.

Aphids

• What it looks like: Clusters of tiny (green, black, or white) soft-bodied 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: Strong water spray knocks them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer (it attracts them).

Desert Southwest Specific Challenges: The extreme heat and arid humidity of the Desert Southwest can stress Tansy, making it more susceptible to pests. Monsoon rainfall can also contribute to fungal diseases if the plant is not well-drained.

Tansy makes a great companion plant for several vegetables in the Desert Southwest garden. It repels pests that commonly bother potatoes, squash, and cucumbers, protecting them from damage. Planting it near raspberries can also deter raspberry beetles. Avoid planting it near brassicas like cabbage and broccoli, as it can attract cabbage moths.