Description
Vernonia gigantea (formerly Vernonia altissima) | Giant Ironweed
Giant Ironweed, also called Tall Ironweed, is an herbaceous perennial wildflower in the Asteraceae family native to the southeast and the central United States and central Canada. It may be found naturally in prairies, grasslands, floodplains, woodlands, along roadsides, and near stream banks or forest edges.
The common name Ironweed refers to the toughness of the stems of the plant, which are erect, stiff, and rounded. The lance-shaped leaves are dark green on the upper surface and paler green and slightly hairy beneath. The plant has a tall and narrow habit and often grows 5 to 8 feet in height, but has been known to reach 12 feet tall! Atop each stem is a flat-headed panicle of flower heads that measures up to 16 inches across. Each flower head has 10-30 florets of showy magenta-purple torch-like flowers that bloom in late summer/early fall. Seeds will form as tiny achenes that have tufts of bristles that are easily dispersed by the wind (like a dandelion seed). Deadheading of the spent blooms will encourage continued flowering.
Vernonia gigantea prefers full sun to partial shade and well-drained moist to wet soils. Tolerant of a range of soil pH and grows well in many types of soils. Effective in cottage gardens, prairie gardens, moist meadows, and makes a spectacular background plant in the border. This is one of the most beautiful flowers late in the season and pictures do not quite do it justice.
The colorful blooms attract an assortment of butterflies and other pollinators. Most small mammals and livestock avoid it due to the bitter-tasting foliage. Deer resistant.
Easily propagated by seed or division of roots. To keep your plants healthy, divide every 3-4 years.
If starting seeds indoors, Ironweed seeds will require a 60 day period of cold-moist stratification before the seeds will germinate. Or if you plan on starting them outdoors you can sow the seeds in the fall and let nature take care of the stratification.
Cold stratification is a term for a procedure that can improve certain seed germination rates by 300-400%. Cold stratification is designed to mimic the winter season’s cold and moist weather that unlocks a seeds protective germination mechanisms and triggers the seed to sprout out of its dormant state. (Most perennial plant seeds (such as native wildflowers) require this combo of cold and damp to germinate.) In nature, this occurs naturally, but by doing the process yourself in a controlled environment, you keep the young seeds safe from any animals that might eat them and they’ll also be less likely to succumb to rot or mildew, leaving more seeds to grow.
There are many methods to cold-stratify seeds, but the two key factors are always moisture and cold. The best and easiest way is to put a small amount of moist/wet sand/soil in a zip baggie and store in the refrigerator for 2 months time (or more). Once stratified, surface sow the seeds (and sand) and gently press into the dirt. Germination will occur with heat humidity and light indoors, or if outdoor, once spring temps and sunlight are adequate. Be sure to plant stratified seeds within a day or so after removing them from the refrigerator because as soon as they warm up they will be ready to grow and may start to sprout.
Type: Perennial
Sun exposure: Full sun to part shade
Mature height: 5-8 ft
Mature width: 2-4 ft
Hardiness zones: 5-9