University of Vermont Extension
OH 66

Fragrant Perennials

By Leonard P. Perry, Extension Professor

Fragrance or scent in plants has been more important historically in gardens, and more recently in Victorian gardens, and is an often overlooked or underutilized aspect in modern gardens. It is an elusive quality, often subtle, and very subjective, depending on each gardener. It is also difficult to describe in plants whether it be from roots, stems, leaves, or--most commonly-- flowers.

Scent is the reaction of certain cells in the nose to volatile compounds emitted by essential oils in plant parts. These oils are found in the surface layers of leaves and petals. Scents are usually described in relation to everyday items with an odor--such as spices, flowers, and fruits--and even unpleasant ones, such as perspiration. Scent is subjective and described by each person as either good or bad depending on personal likes, closeness (what smells pleasant at a distance may be overpowering at close range), or emotion (some 74 emotional responses to flower scents have been described). Due to differences in perceptions, a scent may be classified differently by different individuals.

Scents are elusive in that they are detected in small quantities (often parts per billion) by the human nose, may be fleeting, and often change over time. Scents actually have a function, usually for pollination by insects, but also as protection from insects in some plants or as protection from drought in hot, arid climates (the thick volatile compounds we smell provide a protective layer around leaves). The old English custom of covering brick walls with sprigs of rosemary for cooling has been supported by modern research, which shows rosemary has 74 times the cooling effect of fresh air (thyme has 68 times the cooling effect, lavender 60 times).

The lighter colors of whites, pinks, and yellows have a pleasant but faint fragrance if any, usually attracting moths and butterflies for pollination which see rather than smell. Flowers pollinated by bees also have little or no fragrance and are often blue or contrasting colors such as purple and yellow because bees see rather than smell, and are attracted by these colors (they perceive red and green as grey and unattractive). Composite (daisies) and umbel (queen Anne's lace) flowers often smell unpleasant as these odors attract flies for pollination. Bright colors often attract hummingbirds (which can't distinguish blue from green) and insects (such as flies) and beetles. They may have no fragrance, or--if pollinating insects are scarce--they may have a strong, attractive fragrance. Self-pollinating flowers, which need no insects for pollination, may be bright and often have no fragrance.

In historic times, especially due to lack of sanitation whether from lack of daily bathing to lack of proper garbage disposal, plants--and particularly herbs--were used either to cover body odors as perfumes or to mask room odors as in "strewing" herbs. The latter were scattered about the floor to emit nice smells when walked upon. In medieval and renaissance gardens, many herbs were grown for these purposes as well as medicinal ones. Herbs were worn on the body or clothes, or carried as pomander balls. These uses have been supported by modern research showing oil of cinnamon kills typhoid germs in 12 minutes and other essential plant oils in under 50 minutes. Attar (essential oil) of roses has seven times the antiseptic strength of carbolic acid, oil of thyme 12 times.

In the 1800s and first part of the 1900s, particularly in the Victorian era and "grandma's cottage garden" prior to that, fragrance became valued in gardens themselves, not merely for their functional uses. Fragrant plants were seen as a welcome change from the often stark and polluted times of the Industrial Revolution. It was also at this time that scents were first categorized in 1893 by Count von Marilaun into six groups. Since then, this has been expanded to ten scent groups based on common essential oils to the group. Although there is no "official" classification of scents, these ten are commonly used.

All ten groups are used for flowers.

Leaf scents fall into four main groups, including the turpentine group (rosemary), the camphor and eucalyptus group (sage, catmint, scented geraniums), the mint group, and the sulphur group (mustard, onions, garlic). Of course, other leaf scents can be placed into the ten flower groups, such as some scented geraniums in the lemon and rose groups. Unlike trees and shrubs whose bark and roots generally fall into aromatic or turpentine groups, most herbaceous perennials with scented roots fall into one of the flower groups such as the rose scent of some stonecrop (Sedum) or violet scent of some iris roots.

To fully enjoy fragrant plants in the garden, you should plant them in calm areas out of the wind and breeze. Such areas may also be created under arbors, or by fences, walls, or hedges as in historic gardens. In fact the word "arbor" comes from "herber"--a place where fragrant plants grew. Place fragrant perennials under windows to enjoy their summer fragrance (such as the night-scented evening primroses or catch-fly under bedroom windows) or in patio containers. Consider a water garden with fragrant water lilies. A variety of plants should be used to attract all forms of butterflies, moths, hummingbirds, and bees, and to provide a variety of colors and so of fragrances. Low-fragrant plants (such as many herbs) may be planted along walks where they can be enjoyed, or in lawns and between patio pavers (such as thyme) where they may be enjoyed much as strewing herbs were in the past. And, of course, consider growing fragrant perennial herbs for fall harvest, drying, and subsequent winter uses as in cooking, pot-pourris, lotions, and baths. In this way the fragrant garden can be enjoyed year-round.

Perhaps the most complete reference on scented plants, which has much more depth on all the above topics, is Scented Flora of the World, by Roy Genders, Robert Hale Publisher, London, 1994.

Some perennials with scented flowers:

Edited in March 1998, based on material from 1997.

Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Lawrence K. Forcier, Director, University of Vermont Extension, Burlington, Vermont. University of Vermont Extension and U.S. Department of Agriculture, cooperating, offer education and employment to everyone without regard to race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status.

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Last reviewed April 24, 1998.