Valued for its vibrant purple flower clusters as the gardening season wanes, Vernonia, commonly called Ironweed, is a must have for a pollinator friendly garden, and there are native forms hailing from the midwest and southern Appalachians. The common name may derive from the sturdy nature of its stems, or possibly the bronzy tan coloring of its seed heads that remain well into late autumn. The genus name honors the British botanist William Vernon, who catalogued plants on a visit Maryland in the late 1600’s.
We’ve had a tall form of Vernonia in our garden for a couple of decades. When I say tall, I’m talking 6-8’ tall depending on the soil moisture level that year. We purchased it as Vernonia altissima which is synonymous with Vernonia gigantea. All too often folks shy away from tall plants, but I think that’s a mistake. Looking eye to eye, or even up at the blossoms and pollinator activity adds a dynamic dimension. If you have very narrow planting beds, I can understand being hesitant to add such stature, but there’s a remedy…expand the size of your beds.
There are many Vernonia species (Kew lists over 300), and yes, some have a more restrained height. Take Vernonia lettermanii ‘Iron Butterfly’, which can fool the eye early in the season with its thread- leaf Amsonia-like foliage. It grows to 24-30” in height and becomes covered with purple flower clusters in September.
A number of good hybrids were recently developed at the Chicago Botanic Garden. Vernonia ‘Summer Swan Song’ is hybrid of V. lettermanii and Vernonia angustifolia ‘Plum Peachy’. It grows to about 3’ tall and wide. Vernonia x ‘Summer Surrender’ is similar in appearance but grows larger, up to 4’ tall and wide. A note about ‘Plum Peachy’, we like it for its dark tinted stems but it has proven to be slightly less hardy than its hybrid forms. Perhaps it’s best to grow it in climate zones 6 and warmer.
As mentioned before, there are many other species of Vernonia, but I’ll describe one more. This year we are growing Vernonia crinita (aka V. arkansana) which is also native to the Ozark’s. It blooms a bit earlier than the others, in mid-late August, and grows 5-6’ tall. The clusters of purple asters it produces provide nectar to butterflies and bees.
Vernonia pair well with Ornamental Grasses, Solidago, Eupatorium and Helianthus. They prefer moist soil with good winter drainage, but adapt well to a range of soil types. Vernonia are somewhat deer resistant, but watch for bunny nibbling on the new shoots when they first emerge in the spring. We treat with a rabbit repellent such as Plant Skydd.