Plants produce scents to attract pollinators, repel or poison plant-eating animals, call in predators of pests, protect themselves from heat and disease, and signal to other plants. The molecules behind these smells – mainly terpenes, benzenoids and green leaf volatiles – are the same compounds concentrated in essential oils and the reason herbs taste so good.
Key takeaways
- Plant scents are volatile organic compounds (VOCs) that evaporate easily at room temperature.
- Terpenes such as linalool, limonene, menthol and pinene are the largest group – over 30,000 are known.
- Herbs store aromatic oils in tiny glandular trichomes on leaf surfaces – rubbing a leaf bursts them.
- Flowers time their scent to their pollinators: night-scented plants attract moths, foul-smelling ones attract flies.
- The same compounds that deter insects give us flavour, perfume and medicine.
The chemistry of plant scent
Plant scents are blends of dozens to hundreds of volatile molecules. The main families are:
| Compound group | Examples | Where you smell them |
|---|---|---|
| Monoterpenes | Linalool, limonene, menthol, pinene, 1,8-cineole | Lavender, citrus peel, mint, pine, rosemary |
| Sesquiterpenes | β-caryophyllene, bisabolol, chamazulene | Black pepper, cloves, chamomile |
| Phenylpropanoids and benzenoids | Eugenol, anethole, cinnamaldehyde, methyl salicylate | Cloves and holy basil, fennel and anise, cinnamon, wintergreen |
| Green leaf volatiles | (Z)-3-hexenol | Freshly cut grass |
| Sulphur compounds | Allicin, dimethyl disulphide | Garlic, onions, carrion flowers |
Why herbs smell so strong
Rub a leaf of basil, mint or rosemary and the scent jumps out. That is because many herbs – especially in the mint family (Lamiaceae) – store essential oils in microscopic glandular trichomes, tiny balloon-like hairs on leaf surfaces. Touching or chewing the leaf ruptures them, releasing a burst of aroma.
These oils are primarily chemical defences. Many terpenes are bitter, irritating or toxic to insects, fungi and grazing animals. Thyme’s thymol and oregano’s carvacrol, for instance, are powerful antimicrobials. Mediterranean herbs, which grow in hot, dry places with hungry goats, tend to be especially aromatic.
5 reasons plants produce scent
1. Attracting pollinators
Flowers broadcast scent to guide pollinators from a distance. Each pollinator group has its preferences:
- Bees: sweet, fresh, floral scents (lavender, borage, clover).
- Moths: strong, sweet scents released at dusk – jasmine, honeysuckle, night-scented stock and evening primrose.
- Flies and beetles: the rotting-meat smell of the titan arum (Amorphophallus titanum) and carrion flowers.
- Bats: musky, fruity or fermented scents.
Petunias and snapdragons release scent on a daily rhythm controlled by their internal clock, peaking when their pollinators are active.
2. Defending against herbivores
Strong-smelling terpenes and phenolics deter many insects and mammals. That is why deer and rabbits usually avoid lavender, rosemary and sage.
3. Calling bodyguards
When attacked, plants change their scent to attract the predators and parasites of their attackers. Learn more in how plants communicate.
4. Surviving heat and stress
Isoprene and monoterpenes help stabilise leaf membranes during heat stress and act as antioxidants. Plants in hot climates often emit more volatiles; the blue haze over the Blue Ridge and Great Smoky Mountains comes partly from isoprene and terpenes released by forests.
5. Fighting microbes
Many plant volatiles are antibacterial and antifungal, protecting wounds and flowers from infection – a property humans have exploited for millennia in medicine and food preservation.
Why some plants smell only when touched or at night
Plants spend energy on scent, so they release it strategically. Herbs keep oils locked in trichomes until disturbed. Night-flowering plants save their perfume for moths. Some orchids smell only when ready for pollination, and many flowers reduce scent once pollinated.
From plant scent to essential oils
Essential oils are concentrated volatile compounds extracted mainly by steam distillation (lavender, peppermint, eucalyptus), cold pressing (citrus peel) or solvent extraction (jasmine “absolute”). It can take around 150 kg of lavender flowers to produce 1 kg of oil, and several tonnes of rose petals for 1 kg of rose otto.
Why we love herb scents
Many plant aroma compounds act on our own biology. Linalool from lavender has calming effects in studies, 1,8-cineole from rosemary has been linked with alertness, and menthol from peppermint activates cold receptors (TRPM8) in our skin. Our sense of smell also drives most of what we call “flavour”, which is why fresh herbs transform cooking.
Frequently asked questions
Why do herbs smell when you touch them?
Many herbs store essential oils in tiny glandular hairs on their leaves called trichomes. Touching the leaf breaks these hairs open and releases the aroma.
What are terpenes?
Terpenes are a large family of aromatic compounds made by plants. Examples include linalool in lavender, limonene in citrus and menthol in mint.
Why do some flowers smell at night?
Night-scented flowers such as jasmine, honeysuckle and evening primrose release scent after dusk to attract moths, their main pollinators.
Why do some flowers smell bad?
Flowers like the titan arum smell of rotting meat to attract flies and beetles that normally lay eggs on carrion, tricking them into carrying pollen.
Are plant scents good for you?
Some plant aromas, such as lavender and rosemary, have measurable effects on mood and alertness in studies. Concentrated essential oils must be used carefully.
Sources and further reading
- Pichersky E, Gershenzon J (2002) The formation and function of plant volatiles: perfumes for pollinator attraction and defense. Current Opinion in Plant Biology.
- Dudareva N et al. (2013) Biosynthesis, function and metabolic engineering of plant volatile organic compounds. New Phytologist.
