University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article
Dr. Leonard Perry, Extension Professor
University of Vermont

How do YOU describe scents or fragrance in flowers? There are probably as many ways as there are people, scent being very subjective. Scent varies with personal likes and dislikes, whether it is close or far, or depends on the emotions it evokes. Scientists have devised various means to categorize scents, but one scheme is most common.
It was in the Victorian times at the end of the 19th century that fragrance in the garden became really popular for just that, not for any functional use. Prior to that time, fragrance was used medicinally and to mask unpleasant odors.  It was also at this time (1893) that scents were first categorized by Count von Marilaun into six groups.
Since then, these have been expanded to ten scent groups, all of which are used for flowers. These groups are based on common essential oils for each group of plants. It is the volatile compounds from these oils that our noses register as "scents."
The indole group has flowers smelling like and resembling decayed meat or carrion, such as the skunk cabbage (Lysichiton) and a wake-robin (Trillium erectum), and attracts dung flies for pollination. The aminoid group also smells unpleasant to attract flies, smelling of decayed fish or ammonia, and includes many umbel flowers such as giant fennel. The heavy group smells similar to the last, only sweeter, and includes some of the oldest known fragrant flowers such as some lilies and narcissus.
The aromatic group has some of the most pleasantly scented flowers with scents of vanilla, balsam, almond, and cloves such as in some primroses, peonies, stocks, and pinks. The violet group and smell is, of course, present in violets. Smelling of damp woodland moss, it attracts no insects as the flowers are self-pollinating.
The rose group is pleasant and found in roses in addition to some peonies and scented geraniums. The lemon group is more often found in leaves but also in some water lilies and evening primroses. The fruit-scented group includes many roses and some minor bulbs.
The animal-scented group usually is unpleasant and may smell of musk as in some roses, human perspiration as in valerian and ox-eye daisy, and animal fur as in crown imperial. The honey-scented group is similar to the last, only sweeter, and often more pleasant. Some examples are the butterfly-bush (Buddleia), showy stonecrop (Sedum spectabile), and meadowsweet (Filipendula).
As seen in most of these flower scent groups, insects or pollinators are the main reason for scent.  It basically attracts pollinators specifically needed to pollinate a flower, and at the right time.  Usually if a flower is not ready, or past the time, for pollination, or has been pollinated, it won’t have much fragrance.  If a flower is fragrant at night, odds are that it is pollinated by moths or even bats.  Sweet scents generally attract bees and flies for pollination, while those with fruity or musty-smelling flowers may attract flies or beetles for pollination.
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.
While a species of plant may have fragrance, some of its highly bred offspring may not.  These cultivars (cultivated varieties) may have been bred for other traits instead, such as flower size, shape, or disease resistance.  Roses are a good example of a plant to pay attention to the fragrance of specific cultivars, if this is important to you.  Often, where there are many cultivars to choose from, as with roses, peonies, daffodils or crabapples, some will have fragrant flowers.
If you want a fragrant garden, some of the best choices for spring are lily-of-the-valley, some primroses, and hyacinths.  For annual flowers, consider sweet peas or stocks—both of which prefer cooler parts of the season, heliotrope, flowering tobacco, sweet alyssum (I find this fragrance best for flies), or dianthus.  Fragrant summer perennials include bearded iris early in the season, tall garden phlox later on as well as some of the oriental lilies, and lavender (where hardy).  For woody plants, consider roses, butterfly bush (where hardy), lilacs, crabapples, or the sweet autumn clematis at the end of the season.  

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