SEPTEMBER
2007

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

9-13-07

Night Flowers: Just for the Smell of It

It happens each year around the end of August and the first of September. Local school children head back to school, swallows begin grouping for the annual trek south and the perennial sweet-autumn clematis in my barnyard begins to bloom.

That clematis is one of a group of plants that some gardeners call the night shift. These night-shift plants either flower at night or are fragrant at night. Mostly both. Flowers and the related odors are associated with what biologists call the pollination connection.

The pollination connection is a mutually beneficial relationship between insects and plants. This partnership developed some 225 million years ago when insects began to assist plants in the process of sexual reproduction. Insects became couriers, carrying pollen from flower to flower.

This insect-plant relationship was dependent on guideposts, such as colorful flowers and odors to direct the insect. During the day, the insect pollinators, mostly bees and butterflies, find flowers using vision. At night, the insect pollinators, primarily the moths, are guided to the flowers by scents. Hence night-shift plants, like the clematis in my barnyard, generally have white flowers with an abundance of perfume.

That sweet-autumn clematis is well named. On most any quiet evening this time of year the area around the clematis smells, well, sweet. That sweet odor draws not only the nectar-feeding moths that are effective pollinators of the plant but other insects also intent on a little sip of nectar.

Such after-dark accumulation of flying insects serves to attract nocturnal insect eaters, such as bats and nighthawks. It’s a feeding frenzy of insects sipping nectar, and bats eating insects.

Among the night-flying insects intent on nectar meals complements of the clematis are mosquitoes. Mosquitoes? Yes, mosquitoes feed on nectar. Bats and nighthawks are accomplished consumers of mosquitoes, so any in the odor plume are ripe for eating. Some bats can consume up to 600 mosquitoes per hour. That’s why if you don’t like mosquitoes, it’s nice to have bats around.

But before we celebrate with too much enthusiasm the presence of bats around the flowers at night, consider this. Male mosquitoes are more likely than female mosquitoes to be found seeking nectar. So bats are probably catching more non-biting male mosquitoes than the biting female mosquitoes! Oh well, in my book, if only one of those blood-seeking female mosquitoes becomes a meal for a bat, I’m happy.

My sweet-autumn clematis is technically an evening-fragrant vine. Mock orange is an evening-fragrant shrub. Other plants that perfume the night air include flowering tobacco, fragrant columbine and pinks. All attract the insects of night.

Some plants, such as evening primrose and four o’clocks, have names that reflect that their flowers open toward evening. These plants are sort of hedging their bets by being available for the evening pollinators, as well as the night pollinators. Hawk moths, also called hummingbird moths, are a conspicuous type of insect that can be seen around such flowers.

Night bloomers include a type of cactus called cereus, yucca, and some daylilies. Also any plant with white flowers is likely to be attractive to night-flying insects, because of the ultraviolet radiation reflected from the white color. You can find such plants among impatiens, cosmos, hyacinth, foxglove, poppies and marigolds.

Night-flowering plants are nice to have in your garden. Even if you are not interested in the insects attracted to such plants, the odors they produce make your garden more aromatic. A nighttime garden stroll might provide a dose of aromatherapy. Even if you are not interested in insects or aromatherapy, you can always say your moonlight walk through the garden was "just for the smell of it!"

 

Writer: Tom Turpin
Editor: Olivia Maddox