Spring is in the air and that means an abundance of fragrances from flowers and, while no one ever says, “stop and smell the trees,” a tree can also produce various scents.
Some of the most fragrant trees, like pine trees, are well known. Other trees, like the infamous Tree of Heaven, give off a less enjoyable odour. While trees vary in the scent they produce, there is correlating science behind what exactly makes a tree give off a pleasant aroma or a peculiar stench.
The Basics of Tree Scents
In both trees, and in many other odoriferous species, the chemical source of the scent may be the same. Their leaves, bark, and sometimes wood are rich in organic chemicals called terpenes and terpenoids, volatile oils that are a major component of the essential oils used in perfumes.
What are Terpenes and Terpenoids?
Terpenes are composed of carbon (C) and hydrogen (H) atoms, and they are built from different numbers of isoprene molecules, which have a chemical formula of C5H8. Small terpenes, known as monoterpenes, contain two isoprene units and have a chemical formula of C10H16. Pinene, which has a piney odour, is a monoterpene. Limonene, which has citrusy odour, is also a monoterpene. These two molecules, among others, give conifer trees their distinctive scent. Larger terpenes are known as diterpenes, triterpenes, and so forth, and they can take the shape of long chains or rings.
Terpenes are abundant in conifer resin, and when a tree’s bark is damaged, the resin flows out, hardens, and protects the tree. The terpenes in this resin act as deterrents to herbivores, such as bark beetles who might otherwise feed on the tree, and as fungal growth inhibitors.
Terpenes are also released into the atmosphere over conifer forests on hot summer days, where they can play a role in cloud seeding. Some scientists think that the resulting clouds that form may help to block sunlight and cool the forest.
Terpenes are not only found in trees. Many diverse types of organisms produce terpenes, including insects, marine algae, and sea slugs.
The Best (and Worst) Smelling Trees
Not all tree smells are created equal. Some trees bring up memories of the holidays (pine) or spring (conifer) while others simply smell good.
On the other side of the spectrum are trees that with a smell that repulses rather than attracts. The following are some of the most fragrant trees along with some of worst smelling trees.
The Ponderosa Pine
The Ponderosa Pine is one of the Southwest’s tallest tree in many parts of its range, growing to incredible heights of over 200 feet, with huge trunks 3-4 feet across. It is also one of the most fragrant trees. These woody behemoths grow on dry mountain slopes and mesas. They occur in green, park-like stands on dry, well-drained, and exposed southerly slopes or plateaus.
Ponderosa Pines are easily recognized by the tall, straight, thick trunks, clad in scaled, rusty-orange bark that has split into big plates. One can easily identify some trees by smelling the bark. Ponderosa Pine bark smells like vanilla or butterscotch.
Most people think of common lilacs (Syringa vulgaris) when they consider lilac fragrance, but the scent varies, depending on the lilac variety—from heady and sweet to spicy and intense. Lilac season is fleeting, lasting only three or four weeks. Cut some lilac stems and bring them indoors to enjoy the fragrance while it lasts.
Southern magnolia (Magnolia grandiflora) or evergreen magnolia is another native species of flowering tree renowned for the scent of its blooms. Native to the states of the “Old South,” the five-petaled blossoms of this tree will sometimes grow to 8 inches across. Fully matured, a southern magnolia will grow into a large tree, sometimes 80 feet in height. So if you reside in Dixie and adore the scent of this evergreen hardwood, plant it in an open space where the soil is rich, well-drained, and receives abundant sunshine.
Maidenhair trees, also known as Ginkgo biloba, are one of the oldest known tree species, having existed in its present form for more than 230 million years. The maidenhair name comes from the thin veins on the fan-shaped leaves. These 50- to 80-foot trees display bright yellow foliage in fall to fill the garden with colour.
Female trees begin producing fruit after about 20 years. The fruit creates a slimy mess when it drops to the ground, and the putrid fruit odour is often compared to rotten eggs and vomit. However, male tree don’t produce fruit and select nursery-grown cultivars such as “Fastigiata,” “Autumn Gold,” “Lakeview” and “Sentry,” which are grown from cuttings of male plants to guarantee the gender.
Tree of Heaven
Mentioned earlier, Tree of heaven is among the easiest trees to grow because it tolerates extreme heat and cold and adapts to a wide range of soils. Although its common name would suggest, tree of heaven (Ailanthus altissima) lacks any imperfections, the informal nickname, “stink tree,” perhaps better characterizes this tree. Both male and female trees develop yellow-green flowers. Male trees produce about four times as many flowers as female trees, but the male flowers smell terribly foul and also attract insects.
Native to China and Vietnam, the Callery, or Bradford Pear, became the street tree of choice for American cities beginning in the 1950s. The beautiful flowering tree was disease-resistant and had the ability to grow in diverse climates and soil types. The Callery Tree blossoms in early spring and produces beautiful, five-petaled white flowers — that smell like rotten fish.
Over the years we’ve also learned it’s an invasive species that spreads quickly. So between it’s aggressive nature and putrid smell, we might skip this one in your yard.
What’s That Smell?
With spring in bloom, and summer not far behind, people will get to appreciate trees as they spend more time outside. Now, armed with the knowledge of what makes a tree smell and what types of trees are best known for their fragrance, it will be easy to answer the question, “what’s that smell?” Well…it’s the trees!
Looking to add a fragrant tree to your yard or need assistance with its care, reach out to your local tree service professional.