Field Thistle

Year-round

Field thistle is a tall biennial pollinator plant that tolerates Fort Worth's heavy clay, but it is not confirmed native to North Texas, so grow it as an added pollinator plant rather than a local wildflower.

• Field thistle's core native range is the eastern half of the US and Canada. The University of Texas's own native plant database does not include Texas in its list of native states for this species, so treat it as a non-native addition here, not a local wildflower.
• It grows as a biennial: a low rosette of leaves the first year, then a flowering stalk 2.5 to 6 feet tall the second year before the plant finishes its life cycle.
• It has one taproot and does not spread by underground runners the way the invasive Canada thistle does, so it stays where you plant it and only spreads by seed.
• Fort Worth sits at the eastern edge of the Grand Prairie, where the clay soil runs alkaline and can be 40 to 60 percent clay. Field thistle tolerates both loam and heavy clay, and does best in full to part sun.

It grows 5 to 6 feet tall with spiny leaves, so place it toward the back of a bed instead of along a front walkway or under a window.

Fall

Fall is when spent flower stalks go to seed. Decide whether to deadhead for a tidier look or leave seed heads for the birds.

• Goldfinches and other seed-eating birds favor the seed heads, so leaving some spent blooms standing feeds them into fall.
• This species self-seeds readily, so if you want to keep it from spreading around the bed, cut spent flower stalks back after bloom and before the seed heads open.
• Fort Worth's average first fall freeze lands around late November, per National Weather Service records, and second-year plants finish their life cycle around then.

Cutting the spent flower stalks back in fall keeps the bed looking tended instead of leaving tall dried stalks up through winter, worth doing if the plant is visible from the street.

Winter

Winters in Fort Worth are mild enough that first-year rosettes need no special protection.

• First-year rosettes overwinter as low clumps of leaves at ground level and do not need mulching or covering in Fort Worth's winters.
• Second-year plants finish their life cycle by winter. Clear out the dried stalks once they are fully brown, or leave them a bit longer if birds are still working the seed heads.
• Fort Worth's average last freeze does not arrive until mid March, per National Weather Service records, so hold off on spring cleanup or new planting until after that.

Spring

Spring is planting season in Fort Worth. Get first-year rosettes in the ground once the last freeze has passed.

• Fort Worth's average last spring freeze falls around mid March, per National Weather Service records for the Dallas-Fort Worth area, so hold off on planting tender starts until after that.
• Set new plants or seed in a sunny bed with average to slightly dry soil. Once established, the plant tolerates Fort Worth's clay reasonably well.
• A first-year plant is just a rosette of leaves close to the ground this spring. It will not send up a flower stalk until its second year, so do not expect blooms yet.

Summer

Summer is bloom season for second-year plants, which draw bees, butterflies, and hummingbirds through Fort Worth's hottest months.

• Second-year plants bloom pink to purple roughly June through September, right through Fort Worth's hottest stretch.
• The flowers are a strong nectar source for bees, butterflies, and moths, and they draw hummingbirds too.
• The Lady Bird Johnson Wildflower Center lists this species as a larval host plant for Painted Lady butterflies, so caterpillars showing up on the leaves during bloom season is a sign the plant is doing its job, not a pest problem.
• Water new second-year growth during dry stretches. Once established, plants handle Fort Worth's dry summer spells better than most garden perennials.

Year-round

Field thistle is a tall biennial that handles Dallas's dense Blackland Prairie clay well, but it is not confirmed native to North Texas, so treat it as an added pollinator plant, not a local wildflower.

• This species' native range centers on the eastern US and Canada. The University of Texas's native plant database does not list Texas among its native states, so in the Dallas area it is best treated as a garden addition rather than a native wildflower.
• It is biennial: leaves form a ground-level rosette the first year, then a flowering stalk 2.5 to 6 feet tall shoots up the second year before the plant completes its life cycle.
• It grows from a single taproot rather than spreading underground like the invasive Canada thistle, so it stays put and only spreads where its seed lands.
• Most Dallas County soil is Houston Black clay, the state soil of Texas, which is 40 to 60 percent clay and part of the Blackland Prairie. Field thistle tolerates both loam and heavy clay and wants full to part sun.

At 5 to 6 feet tall with spiny leaves, it reads as a back-of-bed plant, not one for the front edge of a walkway or under a window.

Fall

Fall brings seed set. Decide between deadheading for a neater look or leaving seed heads for goldfinches.

• Goldfinches and other seed-eaters feed on the seed heads, so leaving some spent blooms up into fall gives them a food source.
• The plant self-seeds readily, so cut spent flower stalks back after bloom and before seed heads open if you want to control where new plants pop up next year.
• The Dallas-Fort Worth area's average first fall freeze lands around late November per National Weather Service normals, which is roughly when second-year plants finish out.

Cutting spent stalks back after bloom keeps a front-facing bed looking tended instead of leaving tall brown stalks standing through winter.

Winter

Dallas winters are mild enough that overwintering rosettes need no extra protection.

• First-year rosettes sit low to the ground through winter and do not need mulch or covering in Dallas's typical winter lows.
• Second-year plants have finished their life cycle by winter. Clear the dried stalks once fully brown, or leave them a little longer if birds are still feeding on the seed heads.
• The Dallas-Fort Worth area's average last freeze is not until mid March per National Weather Service normals, so hold spring cleanup and new planting until after that.

Spring

Spring is when to get first-year plants established in Dallas, once the risk of freeze has passed.

• The Dallas-Fort Worth area's average last spring freeze is around mid March according to National Weather Service normals, so wait until after that to plant out nursery starts.
• Choose a full to part sun spot with average to slightly dry soil. The plant tolerates Dallas's heavy clay once it is past the seedling stage.
• In its first spring, expect only a rosette of leaves at ground level. It skips flowering until its second year.

Summer

Second-year plants bloom through Dallas's hot summer, pulling in bees, butterflies, moths, and hummingbirds.

• Bloom runs roughly June through September, spanning Dallas's hottest and most humid stretch of the year.
• Flowers produce heavy nectar that draws bees, butterflies, and moths, with hummingbirds visiting as well.
• The Lady Bird Johnson Wildflower Center documents this species as a larval host plant for Painted Lady butterflies, so finding caterpillars on the leaves in summer means the plant is working as intended, not that something is wrong.
• Deep-water second-year plants during dry spells. Mature plants otherwise tolerate Dallas's summer dry stretches better than many garden perennials.