1 named cultivar

‘Iron Butterfly’Iron Butterfly Ironweed

perennialN. America Native

Threadleaf Ironweed

Vernonia lettermannii

The Story

Plant Bio

Vernonia lettermannii, threadleaf ironweed, is a dense mounding native perennial restricted to Arkansas and Oklahoma, two to three and a half feet high and two to three across. Leaves up to three inches long and an eighth of an inch wide give an exceptionally fine texture, and clusters of small purple tubular flowers open in late summer.

The foliage is so fine it reads as a green mist for most of the season, closer to an ornamental grass than to the coarse ironweeds it belongs with — and it stays under three feet where most Vernonia reach six or more. It grows wild on gravel bars in Arkansas and Oklahoma, so it handles both occasional flooding and drought without complaint.

Uses & Benefits:

A fine green mist of threadlike foliage topped with purple flowers in late summer.

Native, drought-tolerant, flood-tolerant and half the size of the usual ironweeds.

Draws bees, butterflies and hummingbirds late in the season when forage is thinning.

Essentials

At a Glance

Plant Type

Perennial

Height

30 inches

Width

30 inches

Light

Full Sun, Partial Sun

Zones

4, 5, 6, 7, 8, 9

Water

Low to moderate

Humidity

Moderate

Lifespan

Perennial

Native To

Arkansas and Oklahoma

Toxicity

Non-toxic

Planting

How to Grow

Plant in full sun or partial shade in drained soil.
Water while establishing; then it takes drought.
Do not feed; lean soil keeps it upright.
Leave the seed heads for winter structure.
Cut back to the ground in late winter.
Divide only if the clump opens out.

Pro Tip

Do not feed or over-water it — this is a gravel-bar plant, and rich soil makes it flop just as it comes into flower.

Keep It Thriving

Care Guide

Do

Plant it in full sun ☀️
Keep the soil lean 🌱
Leave seed heads over winter 🌾
Cut back in late winter ✂️

Don't

Feed it richly ❌
Over-water an established plant ❌
Cut it back in autumn ❌

Seasonal Care Calendar

Task	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Cutback
Enjoy

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

Native and pollinator plantingRain garden and slope plantingFront to middle of a sunny border

Companion Plants

Little Bluestem Aromatic Aster Goldenrod Coneflower Switchgrass

Multiply

Propagation Methods

Good to Know

Common Questions

Threadleaf Ironweed questions

What zones can Threadleaf Ironweed grow in?

Threadleaf Ironweed is hardy in USDA Zones 4–9. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

Is Threadleaf Ironweed deer resistant?

Yes — Threadleaf Ironweed is rated deer-resistant. Deer typically pass it over, though extreme hunger can override any plant's defenses.

When does Threadleaf Ironweed bloom?

Threadleaf Ironweed typically blooms in late summer through early fall. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Threadleaf Ironweed need full sun?

Threadleaf Ironweed does best in full sun to part shade. In hot climates, afternoon shade keeps blooms fresher longer.

Is Threadleaf Ironweed drought tolerant?

Yes — once established (usually after the first full season), Threadleaf Ironweed handles dry spells with minimal watering. Water deeply its first year to build the root system that makes that possible.