Giant ironweed is one of the most striking native perennials you can grow: tall, bold stems 5 to 8 feet high topped with flat clusters of vivid purple-magenta flowers that hold for weeks in late summer and fall, when the garden needs them. It is native to the eastern United States, from the Mid-Atlantic to Florida and west to Kansas, in damp meadows and along streams, and it is extraordinarily easy, tolerating wet soil, dry soil, clay and part shade with equal indifference.
Plant it 24 to 36 inches apart in full sun or part shade and give it room at the back of the border or in a meadow; cut it back by half in early summer for a shorter, bushier plant that needs no stake. Start from transplants or divisions, since germination from seed is slow and erratic. Water the first season and then forget it. It self-sows modestly and can be divided in spring.
Monarchs, swallowtails, skippers and bumblebees work the flowers constantly, and the fluffy seed heads feed birds and look good standing through winter. It is a host plant for the American painted lady. The bitter foliage keeps deer and rabbits off. The stems cut well with dahlias and late cosmos and last a week in water. Hardy in zones 5 to 9.
Ecoregions:Eastern Temperate Forests
Rust
Orange to brown raised pustules on the undersides of leaves, with yellow spotting on the upper surface. Heavy infections cause leaves to yellow and drop.
Remove and destroy infected leaves. Avoid overhead watering and improve air circulation. Apply a sulfur or copper-based fungicide if it spreads. Clear plant debris in fall.
Powdery mildew
White or grey powdery coating on leaves - usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Fungal leaf spot
Brown or purplish spots on the leaves, often ringed with a yellow halo, that spread and merge in warm, humid, or wet weather; heavily spotted leaves yellow and drop early.
Pick off spotted leaves and clear fallen debris to remove overwintering spores. Improve air circulation by thinning, and water at the base so foliage dries quickly. If it persists, apply a copper- or sulfur-based fungicide at the first sign.
Aphids
Aphididae →Clusters of small soft insects on new growth and flower buds.
Knock off with a strong jet of water. Ladybirds and lacewings are natural predators. Insecticidal soap as last resort.