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Allan designs and plants flowering gardens in Montreal, Zone 5 [USDA Zone 4] .

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Entries in Ironweed (2)


A Purple Autumn Perennial That Pops: Vernonia Lettermannii

Photo credit:The University of Tennessee, Institute of Agriculture

A client gave me a mandate to enhance her flowerbed whenever I find a reliable perennial that blooms in purple.

To please her, I scour my suppliers’ catalogues every spring looking for purple blooming plants. Then I test grow them for a few seasons to determine how they perform. Most are disappointing.  A few become messy or invasive. Some are short-lived plants lasting one or two seasons while others are unable to survive climate conditions in my growing zone.

Happily, this year I discovered that the recently introduced Vernonia lettermannii  - also referred to as Narrow-leaf Ironweed - meets my rigorous requirements for neatness and low maintenance. I intend to surprise my client by planting it in her garden this coming spring.  

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Although it is dramatically shorter than the species Vernonia arborescens or the variety Vernonia mammoth, lettermannii provides a far more intense color display than either of its taller cousins. It blooms in August and September in a bright true purple that projects from afar and happily holds its color in the August sun.

Unlike its taller relatives that fade as they age and shrink from view, the florets of lettermannii hold their form and maintain a vivid color [albeit slightly more reddish] long after dormancy sets in. By October, the flower heads may have long expired but their rich color, now on slightly scrunchy petals, sustains itself for another few weeks.

Here are several photos from this past season of Vernonia lettermannii  in one of my October flowerbeds:

Vernonia lettermannii satisfies gardeners’ needs on several fronts. It is a butterfly and hummingbird magnet. It feed a passion for purple flowers both when in bloom and into creeping dormancy and it enriches the color story of the autumn garden by extending the bloom season well into October.

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An additional attribute is its magnificent feathery foliage. In late spring, the perennial shoots up to create a large, soft mound of glossy-green foliage that is enchanting to behold and heaven to touch. Throughout the growing season, this visual delight continues to add to the garden a] sumptuous architectural detail - think round but softer boxwood plants - and b] feathery sensuality like Amsonia hubrechtii.

Cold hardy in USDA Zones 4  [CND Zone 5] Vernonia lettermannii is a heat tolerant plant that grows two or three feet tall and wide in full sun, even in poor rocky soil, under average to dry conditions. Good drainage is required. Periods of inundation are tolerated, but not heavy or saturated soils.

Few if any retail nurseries stock Vernonia in any of its varieties. Consequently, all the varieties growing in my garden were purchased from mail order suppliers.

Here is how online seller Plant  describes this flowering perennial :-

Vernonia lettermannii is a fascinating ironweed that hails from Arkansas and Oklahoma where it can be found in rocky soils and on rock outcrops. Imagine taking an Amsonia hubrichtii, shrinking it to 2' tall x 2' wide, shearing it into a round ball, then topping it with hundreds of purple flowers in August and early September, and you have Vernonia lettermannii...a hummingbird delight. We grow this in our hot, dry, scree garden where it has caused visitors to lust in their hearts.

The seller’s words above are not hyperbole. Although the variety lettermannii  is much shorter than the species, it  produces a far more dramatic color display than any of  its taller cousins and it holds that color long than they do - even after it goes dormant.

At that time of year, while the gardener is mournfully anticipating the falling leaves of autumn and when there is little or no color left in the fall flowerbed, Vernonia lettermannii can cheer the heart and  take one’s breath away.


A Tale of Two Tall Plants

Vernonia noveboracensis, I discovered Vernonia noveboracensis last year, my excitement was fueled by the height and color of the plant. Only a handful of perennials grow as tall as this one does, [ 6-8 ft. (1.8-2.4 m)] especially at the end of summer, when most lofty plants bloom in gold or yellow. I found it at the nursery, lying on its side like an invalid, because it had outgrown its seedling-sized pot and was root bound. It was planted in my garden in August of 2009, with an expectation that it would establish itself and deliver impressive results by August 2010. That did not happen. Clearly, this infant perennial needed more time to mature and its lack of presence in my garden a year later was disappointing. One tall stalk grew where I had expected several and that stem had only a modest amount of branching florets. Part of my disappointment lay in the fact that the color of its blooms, a muted violet magenta, does not have the brilliance to project itself over long distances. I came to the conclusion that unless one admires this plant up close, it makes no statement at all.

Vernonia only looks this rich in photos. image: negative impression was short lived. A few days after it bloomed, I began my vacation and found myself in a public park in downtown Zürich where Vernonia was the star attraction. What a shock to see this plant at center stage. It had been planted as part of a larger flower composition, now mostly gone to seed, and remained the only perennial still in bloom. To my surprise, it looked impressive. A long row of twelve mature Vernonia formed a lush backdrop to the original composition. What I learned in Zurich is that this perennial can be visually effective when it is mature, with many brackets of blooms, and when planted in drifts. Distributing plants in drifts is a garden design technique that produces dramatic results. However, it requires architectural perennials like Vernonia that can also supply winter interest. The challenge, going forward, is to find a way to incorporate drift planting into small residential gardens.

A combination of Vernonia, Water Canna, and Eupatorium. Photo by Joe Henderson for Chanticleer Gardens, Pennsylvania, the time I returned home, my own Vernonia florets were spent and I decided to leave them uncut so that I might be able to differentiate this plant from other spent stalks that grew nearby. That decision turned out to be wise because later in autumn, the Vernonia dead heads morphed into cinnamon-colored feathered seed pods that shimmered in the sun. This visual and textural interest was a bonus that I could have never imagined.

Boltonia. The flowers in my garden never look this pink. Photo: the far end of my garden, another story was unfolding where only a few months before I had planted Boltonia. In my never ending search for tall perennials, I purchased a seedling at the nursery in order to experiment with it in compositions. For many years, I had seen this plant in other gardens and never found it attractive. It reminded me of a giant weed. Even the pink color of its flowers looked insipid in the sun. What an irony that a plant should be so distorted by the very thing that it needs to survive. Nevertheless, I had wanted to see how it would perform in my garden setting and had hoped to be inspired by its height. It did no better in my garden than it did in others. Even though it was tall [4 to 5 feet] and architecturally majestic, it remained unimpressive in bloom. That it needed to be staked early in its growth, just like a Delphinium or Aster Alma Potchke, did not earn it high marks either.

PerovskiaHowever, it did occur to me, that if I were to lift and move it to the other side of the garden, in front of or behind Vernonia, perhaps the two plants might enhance each other. I am trying to imagine if the juxtaposition of pale pink and violet magenta will help improve the color projection of both plants.


Helianthus, photo Lone Willow Farms I am also inspired to add silver blue Perovskia in front of the Vernonia and lemon yellow Helianthus nearby. The possibility that I might generate color synergy between the four perennials intrigues me and I have placed that project on my to-do list for next season. It’s a wonder how these ideas keep percolating upward now that it is too late to act upon them until next spring.