Standing 4 to 6 feet tall at maturity, ironweed boasts a big garden presence when it begins blooming in late summer. That's because clusters of bright purple flowers decorate its tall stems for 6 weeks or more at the end of the growing season. Ironweed received its common name from its ironlike qualities: tough stems, tenacious growing habit, and flowers that give way to seed clusters the color of rust.
Ironweed provides nectar loved by pollinators: long-tongue bees, flies, skippers, and butterflies such as monarchs, swallowtails, and American painted ladies. It also provides a food source for caterpillar moths.
Ironweed Overview
Where to Grow Ironweed
Low-maintenance ironweed grows best with full sun and rich, moist almost acidic soil. Sunny, moist beds and borders, rain gardens, low areas, and stream banks suit it well. This perennial also thrives in casual cottage gardens, native prairie gardens, meadows, and other naturalized areas. Ironweed's bitter foliage makes it undesirable to most grazing animals, so it is considered a weed in pasture plantings.
How and When to Grow Ironweed
The quickest way to enjoy this native plant in your landscape is to start with a nursery-grown plant. Plant it in the spring after the danger of frost has passed.
Prepare the planting area by amending the soil with organic matter. Dig a hole at least twice the size of the plant’s root ball and place the plant in the hole. Backfill it with original soil and tamp it down. Water thoroughly and regularly until the plant is established.
Ironweed spreads readily through self-seeding. Limit its spread by snipping off flower heads before the seeds develop.
These are large plants when fully grown. When planting several, space them about 2 feet apart. Reduce the overall height of mature plants in late spring by cutting young stems back almost to the ground.
Ironweed Care Tips
Like all native plants, ironweed is pretty care-free once it is established.
Light
Ironweed grows best in full sun, especially in the northern reach of its hardiness zone. In the south, it tolerates partial afternoon shade as long as it gets at least 4-6 hours of morning sunshine a day.
Soil and Water
Ironweed is pretty adaptable to most soils but prefers moist, well-drained, and humus-rich soil that is slightly acidic. Infertile, dry soil is the only condition that will not support ironweed.
While mulching helps to retain soil moisture, the plant still needs to be watered if the soil is not naturally moist. Give it at least an inch per week through rainfall or irrigation.
Temperature and Humidity
As a native prairie plant, ironweed is both winter hardy and tolerates high heat and humidity within its hardiness zones. During dry periods it will need ground watering to thrive.
Fertilizer
Ironweed prospers with little to no additional fertilizer. If you want to give it a boost, add some compost to the root zone in the spring.
Pruning
After ironweed blooms, snip off the spent flowers to limit self-seeding. You can also harvest the flowers for bouquets. After the bloom period is over, cut the plant back to ground level.
Potting and Repotting Ironweed
Like many tall natives, ironweed is typically not grown in pots for a reason—it looks best in the landscape and it gets tall and wide and is prone to toppling over. If you decide to grow it in a pot, choose one made of a heavy material (terra-cotta or ceramic) and make sure it has large drainage holes. Use well-draining potting mix and water it daily, in hot weather even twice a day, to keep the soil moist.
When the plant starts to crowd the sides of its pot or grow out of drainage holes, it’s time to repot. Choose a container that’s one size larger and fill with fresh potting mix. Transfer the plant and fill in with soil, watering well to remove air pockets.
Despite their hardiness in areas with cold winters, when grown in pots, ironweed roots are exposed to the cold. As a protective measure, winterize the pots by sinking the container into the ground. You can also place the container in a second, larger pot to create a planting silo that will insulate the roots from the cold or move the container into an unheated shed or garage.
Pests and Problems
As a native plant, ironweed is resistant to most pests and diseases. Occasionally aphid and Japanese beetles attack the plant. Deer and rabbits rarely browse on ironweed.
How to Propagate Ironweed
The easiest method of propagating ironweed is by division. In the early spring, dig up the root and divide it into smaller sections. Plant them in new locations at the same depth and water them well until you see new growth. It is not unusual for the plant to take a couple of years or longer to get established and bloom.
To grow ironweed from seed, direct sow the seeds in your garden in the fall. Plant them about 1/8-inch deep, cover, and leave them to overwinter. The seeds will germinate in the spring. To start your seeds indoors, you will need to stratify the seeds for successful germination. About four months before the average last frost date in your area, place the seeds in small pots filled with seed-starting mix and lightly cover them. Cover the pots and refrigerate for about 3 months. Then, remove the pots and place them, uncovered, in a bright, warm spot until seeds germinate. Keep soil moist and tend the plants indoors until they reach at least 2 inches tall.
Seedlings (whether grown from seed or cuttings) can be transplanted outdoors once soil temperatures are reliably above 65 degrees. For a smoother transition, harden your seedlings off by placing them outside for a few hours a day (for 5 to 7 days) and increasing the outside exposure a little more each day.
Ironweed Companion Plants
Ironweed provides nectar loved by pollinators: long-tongue bees, flies, skippers, and butterflies such as monarchs, swallowtails, and American painted ladies. It also provides a food source for caterpillar moths. Create an oasis for these vital members of our ecosystem by planting ironweed alongside other pollinator plants, such as giant hyssop, smooth blue asters, threadleaf bluestar, baptisia, and Culver's root. In addition to planting for pollinators, rely on native plants and you can enhance your backyard habitat by eliminating the use of pesticides. Try planting ironweed with these tough natives.
Goldenrod
Known for its bright yellow flower spikes, goldenrod lights up gardens when it blooms in late summer to fall. It's very attractive to bees and butterflies and also makes for a good cut flower. Goldenrods are generally good flowers for clay soil and they can grow up to 5 feet tall. 'Crown of Rays' is just as pretty but stays more compact at 2 feet tall. Zones 4-8
Purple Coneflower
A butterfly-and-bird magnet for sunny sites, purple coneflower is an easy-to-grow perennial native to many prairies, meadows, and woods in the United States. Its showy daisy-like flowers bloom atop stiff stems with dark green leaves that make a great fresh-cut bouquet. Also, look for hybrids with colors ranging from pink to white, orange, burgundy, and red. Zones 3-8
Little Bluestem
A gorgeous ornamental grass from the North American prairies, little bluestem bears blue-green foliage that turns crimson in fall. Purplish-bronze flowers appear on branched stems above this plant's foliage, followed by clusters of fluffy, silvery-white seed heads. Zones 3-9
Blazing Star
A must-have perennial for butterfly gardens, blazing star is a native prairie plant that has become a popular cut flower. It offers spikes of fluffy, deep purple flower heads atop leafy flower stalks. This plant is an attractive addition to containers, cutting gardens, flower beds, and naturalized plantings. Zones 3-8
Frequently Asked Questions
- Is ironweed invasive?Like most native plants, ironweed is not invasive within its range but it can self-seed aggressively wherever conditions are favorable. Keep the plant in check by deadheading flowers before they develop seeds and removing volunteer plants.
Like most native plants, ironweed is not invasive within its range but it can self-seed aggressively wherever conditions are favorable. Keep the plant in check by deadheading flowers before they develop seeds and removing volunteer plants.
- Is ironweed safe for pets?While ironweed is not palatable to grazing animals, it does not have any toxic properties for humans or pets.
While ironweed is not palatable to grazing animals, it does not have any toxic properties for humans or pets.
- Do monarch butterflies eat ironweed?Ironweed nectar will draw monarch butterflies along with many other pollinator species.
Ironweed nectar will draw monarch butterflies along with many other pollinator species.