Lobelias for Your Landscape

Late summer is probably not the most exciting time to hike through our native woodlands. Weekend rambles present varying shades and textures of green. It’s pleasant, but not engaging. A cool breeze may flutter a yellow leaf or two to the ground, a mere portent of the colorful autumn-kissed leaves to come. Then suddenly, across the greenness, a brilliant scarlet spike appears. It’s nearly luminous – it’s lobelia!

Specifically, it’s cardinal flower, Lobelia cardinalis, named, like the songbird, after the bright red vestments of the clergy. And surely, in all nature’s palette, no other wildflower can compare with the sheer intensity of its fire-engine red color. Even in the deepest shadows of a quiet marsh, the chest-high racemes of its flowers flash out like beacons across many hundreds of feet.

Cardinal flower is all the more remarkable as red is seldom found among our flowering native plants. Yellow, white, pink and purple: sure -- but seldom red, save for the odd bee balm. And when added to the lackluster canvas of a waning summer, you’ve got a bona fide phenomenon.

Botanically, cardinal flower is an herbaceous perennial, best suited to moist areas like stream banks and wetlands, as well as moist woodlands and meadows. The plant and its cultivars can also thrive in a garden setting, even in full sun, although the soil must be kept evenly moist. Applying a layer of mulch can help, although it might be best to select a site with filtered light. Cardinal flower can easily survive flooding and the soggiest of yards, but it will not tolerate drought or excessive heat.

There are some important cultural notes to consider when growing cardinal flower. For one, the plant, while long-blooming (until frost) and perennial, is unfortunately somewhat short-lived, lasting roughly three years. However, the plant readily self-sows, and will produce a substantial number of seedlings year after year to keep the lobelia colony growing. Two-celled seed capsules are formed in mid to late autumn, split open and scatter numerous tiny seeds upon the ground. Those seeds will sprout in spring, although they do require exposure to light. Therefore a heavy layer of mulch might prevent reseeding.

More importantly, mulching might smother the basal rosette of leaves that hug the ground in winter, after the central stem has died back. That might hinder growth early in the year, or even cause crown rot and the death of the plant.

Cardinal flowers can also be propagated by dividing large established clumps, or by separating basal offshoots from the mother plant in fall, after the flowers have faded. And much as you cannot have red states without blue states, our scarlet-blooming cardinal flower is complemented by a twin species: great blue lobelia (L. siphilitica).

Both lobelias share a wealth of splendid features, such as easy propagation and care, and both bring a burst of color into the natural landscape when it is most appreciated. However, to its credit, great blue lobelia is generally more forgiving of moisture and heat conditions, and even more flexible in garden uses.

The flowers of both plants feature long tubular florets uniquely adapted to pollination by hummingbird. The relationship is especially symbiotic as the ruby-throated hummingbird is significantly dependent on the nectar from these late flowering plants to keep them “fueled” during their migration south. The flowers are also popular nectar sources for the spicebush, pipevine, and black swallowtail butterfly.

Our lobelias have also played an important medicinal role among Native Americans, who used different portions of the plants, from leaves and seeds to mashed roots and stems, to create poultices and infusions to treat headaches, nosebleeds, typhoid, respiratory ailments, common colds, and even as a culinary preventative for divorce. In fact, the botanical name of blue lobelia is derived from its use in treating venereal disease.

Of course, our lobelia cousins have been subject to hybridization over the years, and there are a number of truly striking cultivars available, often referenced as Lobelia x speciosa, including one of the most popular hybrids: ‘Queen Victoria’ with scarlet flower spikes up to three feet tall rising above bronze foliage. ‘Bee’s Flame’ offers bright red flowers and purple foliage, as does ‘Dark Crusader.’ ‘Russian Princess’ is another very popular selection with magenta flowers and maroon foliage. ‘Alba,’ naturally, is a white-flowering cultivar, while ‘Twilight Zone' and ‘Heather Pink’ have soft pink flowers, and 'Angel Song' is a blend of muted creamy salmon.

Beyond our two native subjects, there are almost another 360 species of lobelia found worldwide, including several popular garden favorites. Chief among these is Lobelia erinus, commonly called edging lobelia, which comes in two useful forms, both attractive to butterflies and profusely covered with small, intensely colored flowers in midnight blue, purple, violet, scarlet, rose, pink or white, often with bronze or greenish-bronze foliage. A fast-growing trailing variety features long, sprawling stems covered with half-inch wide flowers which gracefully cascade over the sides of hanging baskets and window boxes, or add a touch of casual elegance to formal container plantings.

The compact, bedding variety is forms dense, brilliant mounds about six-inches tall, ideally suited for use as a ground cover, an edging plant along sunny or partially-shaded pathways, tucked into rock gardens, or artfully blended together in lush masses of mixed colors. Blur your vision while looking at such a planting and you’ll think you’ve slipped into a Monet canvas! Most garden centers carry a large selection of flats in spring, including such varieties as ‘Paper Moon,’ ‘Monsoon,’ ‘Rapid Blue,’’ Crystal Palace,’ ‘Lilac Dream’ and 'Horizon Light Pink.'

Whether red or blue, native, hybridized, or introduced, there is surely a lobelia (or five or six) that would make a welcome addition to your landscape. And if you go native, remember that you’ll also soon welcome those ruby-throated hummers, and the fluttering color of butterflies.

Copyright 2009, Joseph M. Keyser