There is nothing like the scarlet red color of a cardinal flower, Lobelia cardinalis, in bloom along a stream bank or lakeshore in late summer. Besides being one of my favorite flowers, it is also a favorite of the ruby-throated hummingbird. And while as many as 19 species of plants found in the Eastern US have probably co-evolved with hummingbirds, the cardinal flower is the most well-known. The range of the ruby-throated hummingbird and the cardinal flower are very similar, demonstrating how closely the two are linked. The long tubular flowers of cardinal flower and the long, narrow bill of a hummingbird are a perfect match. By reaching all the way down into the bottom of the five-petaled flower in search of nectar, the hummingbird gets food, and in return, the cardinal flower gets pollinated.
Hovering mid-air, the hummingbird laps up nectar with its long tongue from the bottom of the tubular flower. While doing so, it brushes up against the flower, getting pollen from the stamen stuck to its feathers, which it then inadvertently transfers to the pistil of another flower – in the same way a honeybee pollinates flowers. Many hummingbird pollinated flowers have long, tubular flowers with long stamens, which are the male flower parts carrying the pollen. That way, the pollen is brushed off on the hummingbirds’ forehead as it reaches in to take a sip.
In the case of cardinal flower, besides the unique relationship between the shape of the flower and its main pollinator, the flower is also ‘protandrous’ – meaning the flowers start off as male and then become female.
The male, pollen producing stamens develop first and stick out. As the stamens fade, the female pistils develop and stick out in their place. This ‘sex change’ occurs from the bottom up along the stalk of flowers. The male flowers are the most nectar rich, so the hummingbirds visit them first, spending most of their time at the top half of the stalk of blossoms. So the hummingbird transfers the pollen from the newer blossoms that are still male to the older blossoms that have turned into female flowers – all on the same plant.
While hummingbird favorites tend to be red, orange, or pink in color, they will visit other colors including white and blue. One rainy afternoon at the nursery, I sat and watched a hummingbird visit the small, white bell-shaped flowers of Solomon’s seal in the shade, protected from the rain by the large sugar maple trees above. Other white flowers that hummingbirds are known to visit include Tall White Beardtongue, New Jersey Tea, and Summersweet.
Ruby-throated hummingbirds migrate to the eastern US every spring form their over-wintering ground in Central America and Mexico. Once they arrive in NY in the spring, early blooming flowers such as pinxterbloom azalea and wild columbine are important sources of nectar. Beebalm, bergamot, beardtongue, and trumpet honeysuckle are great nectar sources during the summer. Cardinal flower and other late blooming flowers such as the orange colored spotted jewelweed become important nectar source for late summer/early fall – as hummingbirds are beginning to prepare for their fall migration. And the reward is worth all the hard work – the sugar content for hummingbird flowers averages 26% – more than twice the amount of sugar in a soda!
Cardinal flower makes a stunning addition to the garden. Or you can even enjoy them in a planter if you like. I keep one on the porch. While often considered a perennial, Cardinal flower is not actually a true perennial. The plant and associated roots die after going to seed. However, new offsets grow from the axils of the lowermost leaves, putting down new roots. So it is these new young plants that overwinter as rosettes and then bloom the next summer. In northern climates, including New York, sometimes it can be a bit tricky to get these new young plants to overwinter. A little extra care, and some mulch to help protect it, should do the trick. And they are well worth the extra effort to enjoy their beauty in late summer. In moist areas, cardinal flower also readily reseeds. Hardy in zones 3-9, I usually see cardinal flower along stream banks and lakeshores, however you can grow it in the garden in an average soil, it just won’t reseed in and spread on its own.
Popular nursery cultivars, such as ‘Queen Victoria’, are usually hybrids the Mexican species of Lobelia, and are not usually hardy for this area – so watch out. Be sure to check the plant label, and make sure you are getting Lobelia cardinalis – our native cardinal flower. The hummingbirds will thank you!