Making Sense of Pelargonium Scents

Making Sense of Pelargonium Scents
By William Scheick
Contributing Editor

Error is a hardy plant,” Martin Farquhar Tupper wrote in his long-ago popular “Of Truth in Things False” (1838). His sage metaphor seems especially applicable to so-called geraniums, enormously popular plants bearing an erroneous common name. Although these supposed geraniums are actually pelargoniums, the widespread misnaming of them has proved to be as hardy as a lawn weed. Just mention the word “geranium” and typically the pelargonium impostor comes to mind.

This misunderstanding began in the 1600s, when the Dutch East India Company first imported South African pelargoniums to Europe, and this widespread misperception isn’t likely to change anytime soon. Even books about these perennials dodge the word “pelargonium” on their covers. Instead, for example, their titles read Geraniums: The Complete Encyclopedia and Scented Geraniums, a marketing pattern that might appeal better to some potential buyers but hardly helps to set the record straight in gardeners’ minds.

In fact, this misidentification remains so strong that the reality of true geraniums can come as a surprise to some gardeners. True geraniums, the woodland natives also known as cranesbills, do not look like pelargoniums even though both genera belong to the family Geraniaceae. True geranium flowers, for instance, usually feature floral forms similar to primrose blooms, whereas pelargoniums erect spikes tipped by clusters of flowers somewhat reminiscent of winged insects, particularly butterflies.

Whatever they have been called, pelargoniums have remained popular garden selections for centuries. At first, early-European gardening interest focused on the wild species of these plants, especially Pelargonium zonale. By the middle of 18th century, however, P. zonale hybrids dominated the garden scene.

Today zonal hybrids continue to star as bestsellers, while the more basic native pelargoniums have slipped into obscurity. “Species pelargoniums,” as collectors refer to them, are the plainer ancestors of today’s fancy hybrids. Although about 200 species pels exist, many of them tend to be hard to find commercially because their marketing value remains limited. With the exception of those valued for their scent, species pels primarily fascinate gardeners on the lookout for uncommon plants. I have occasionally wondered, only half-seriously, whether these sidelined “wallflowers” perhaps attract gardeners who feel sorry for “rejected” plants.

Species pels often do look like plants in need of rescue and tender-loving care. Their foliage tends to be sparse with an open overall form. Sometimes, as with lavender-flowered P. hirtum, they give the impression of a bungled parsley imitation.

Likewise, the spiked flower heads of species pels hardly make a case for them. Their floral display remains smaller and less abundant than those produced by contemporary floriferous pel hybrids. Even so, for some gardeners this very difference accounts for one of the charms of species pels, proving that tiny flowers sometimes appeal to humans as much as to their pollinators.

Although species pels are not common at local nurseries, their seeds can be purchased through internet contacts. The most available species include: P. acetosum, a sorrel-like shrub ornamented by clusters of two to seven salmon-pink flowers; P. carnosum, a bonsai-like succulent with small cream-hued blooms highlighted by pink nectar guides; P. cordifolium, a heart-leafed plant bearing cute lavender blossoms with wide upper petals adorned with dark nectar guides; P. echinatum, a low-growing, thorny succulent with fuzzed leaves and white-to-pink flowers with a heart-shaped red spot; P. graveolens, a rose- or lemon-scented two-footer with small, purple-spotted, pink-white blooms and trailing ruffled leaves; P. multicaule, a creeping, short-lived perennial with tiny pink, magenta-striped blossoms; P. salmoneum, a sandy-soil, part-shade perennial with salmon-hued flowers; P. suburbanum subsp. suburbanum, a fast growing, mat-like plant with long-lasting pink blooms; P. tetragonum, a creeping square-stemmed succulent with red-margined leaves and white-pink blossoms; and P. tomentosum, a peppermint-scented trailer with tiny white flowers and large velvety leaves.

Species pels divide into two types, succulent and tuberous. Both store water, enabling them to withstand periods of dryness. Both insist on rapidly draining, compost-rich potting mixtures, and neither type tolerates damp, rainy conditions. Morning watering (without wetting their foliage) proves best, but only when their soil feels dry. To avoid a judgment error, I use an inexpensive water meter.

With thick stems and fibrous leaves, the succulent-type pels can withstand heat and direct-sun exposure better than the tuberous type. Most of us grow tuberous pels, which include the scented varieties. Some tuberous types cannot tolerate too much humidity, while others struggle in too much heat. To flower, however, pels require some exposure to sunlight during spring and autumn, usually their high-performance seasons. The tuberous types go dormant during our summers, when they should be kept dry and shaded. When dormant, they sometimes look like dead sticks. All pels must be protected from frost by indoor overwintering — also the best time to prune their yellowing leaves and stalks.

For most Texans, the prime seasons for pel performance can be compromised when hot weather ratchets up much too quickly during spring or lingers seemingly forever during autumn. On the other hand, they perform wonderfully during winter in South Texas.

Our pels do best, then, when allowed direct-sun exposure only during the morning followed by bright afternoon shade. All-day dappled light — such as beneath live-oak canopies — also works. Sinking their pots into the ground or a mulch mound reduces the desiccating impact of warm wind. Adding an inch-deep layer of pine-bark mulch around each buried pot helps keep tuberous-pel roots cool, and these roots actually prefer to be moderately pot-bound. Pel roots rot when overwatered. In Texas, however, hydrating them thoroughly when truly dry and feeding them lightly after summer dormancy aid their performance. As strange as it might seem, regular irrigation and feeding usually shorten the life of pels.

Today’s gardeners find the showy zonal, angel, ivy-leaf and regal selections far more alluring than species pels. These newer jazzy selections stem from decades of selectively crossbreeding the plainer species pels for special effects.

At least today’s retailed scented pels often remain fairly close to their more basic species lineage. Some actually are simply species pels, such as orangey P. graveolens ‘Citriodorum’ and piney P. denticulatum. Others are cultivated varieties of species pels, including P. capitatum ‘Pink Lemonade.’ Like species pels, today’s scented selections tend to bear fewer and tinier flowers than the fancier pel hybrids. To make up for less showiness, however, some scented pels produce a variety of appealing fragrances inherited from their wild ancestors, which (incidentally) exhibit a decent level of heat tolerance on their own in nature.

We frequently associate scent with flowers, although in fact foliage often releases the volatile chemicals we regard as fragrance. That’s the case with pels, which possess aroma-emitting leaves. The selections retailed specifically as “scented-leafed” belong not to a botanic category but to an artificially designated marketing group defined solely by fragrances we favor.

These preferred fragrances include citrus, peppermint, rose, cinnamon, nutmeg, ginger, peach, apricot, apple, strawberry, coconut, pineapple and even celery. There are, as well, other pungent and not quite identifiable scents — some considered distinctly unpleasant. Interestingly, people regularly differ about what smell they detect despite a market tag informing them what fragrance they should identify.

Pel leaves possess tiny hollow glandular hairs (trichomes) with fragile tips that easily break when touched or brushed. Once broken, these hair tips secrete oil from their base located inside the disturbed leaf. As this oil volatilizes, we perceive it as fragrance. This oil provides sunscreen for pel leaves and also helps pel foliage to retain moisture during hot days. Unpleasant-tasting, this oil certainly deters predation.

So, with pels as with rosemary and agastache (hyssop), the biological utility of unpleasant-tasting leaf oil is hardly mysterious. On the other hand, precisely what advantage leaf scent gives a plant remains uncertain. Volatilizing chemicals released from distressed leaves (research shows) chemically signal nearby plants of the same species to adjust their own enzymes (usually toward bitterness) in readiness for attack. Possibly, too, as in the example of our native lantana, leaf odor is designed to deter smell-sensitive animals from sampling the plant, leaving the actual oily bad-taste experience as a back-up (rather than a primary) disincentive. After all, it would be better for a plant if animals walked away from it on first “stinky” encounter rather than after taste-testing some foliage before giving up on it as a food source. No damage is better than some damage.

Why scented pels have developed so many different fragrances remains much more puzzling. Maybe unique scents attract specific pollinators or maybe they summon territorial insects, such as ants, to aid the disturbed plant by dispatching a munching invertebrate or warding off some larger intruder. Whatever the reason, pel scent has obviously also enticed gardeners, the plant’s ultimate territorial guardians (so the speak). After ornamenting late-winter and early-spring home landscapes, long-lasting scented-pel foliage has been used medicinally or tucked into sachets and potpourris. Besides some culinary value, scented pels also contribute fragrance to a night garden during warm evenings.

Unfortunately, not all scented pels live up to the fragrance promised on their market tags. Actually, many are inadequately labeled — either misnamed or renamed to increase commercial appeal. A selection’s exact parentage tends to remain obscure. So much crossbreeding (hybridization) has occurred over so long a period that it is now very hard to classify many of the marketed pels.

Also disconcerting, a particular pel can produce more than one fragrance and can also vary in intensity of aroma. Plant fragrance tends to become strongest in warm temperatures. As a result, for example, a scented species pel such as P. denticulatum might smell (pleasantly) like balsam/pine or (less pleasantly) like Pine Sol, depending on the weather. So, apparently, savvy collectors of scented pels shop on warm days and gently rub a leaf to sample its perfume before purchasing a plant. For them the rule of thumb is “sniffer beware,” a gardening version of caveat emptor (buyer beware).

While only individual preferences can determine which plant will delight, some pels have proven to be widely reliable based on their promised scent. That’s the case with aptly named ‘Old Fashioned Rose,’ ‘Pink Lemonade,’ ‘Ginger Frost,’ ‘Chocolate Mint,’ ‘Apple Cider,’ ‘Almond,’ among others. Whether ‘Gooseberry Leaf’ smells like a peach or ‘Paton’s Unique’ smells like an apricot can spark a patio discussion — the sort of conversation that scented pels often instigate.

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