The question "do plants hear?" is intimately tied to understanding what hearing actually is. In animals, hearing is the perception of air pressure variations (sounds) through specialized organs (the ear) connected to a nervous system that processes acoustic information and produces behavioral responses. Plants have nothing analogous to this strict definition. However, they do have the capacity to perceive mechanical vibrations in air and soil through mechanosensitive channels present in every cell, and to respond to certain vibrations with physiological changes. Whether this constitutes "hearing" depends on the definition you use.

Plant physiological responses to acoustic vibrations: experimental evidence

Response to pollinator wing sounds (Veits et al., Science 2019): researchers from Tel Aviv University (Yosef Pollak, Lilach Hadany) demonstrated that flowers of Oenothera drummondii (an evening primrose) increased nectar sugar concentration by approximately 20% within 3 minutes when exposed to recordings of bee buzzing. The response was frequency-specific: only frequencies in the bee buzz range (150–500 Hz) were effective. Higher and lower frequencies produced no response. The hypothesized mechanism: floral petals (which are bowl-shaped) function as acoustic resonators that amplify vibrations within the bee frequency range. Petal vibrations activate mechanosensitive channels in nectar-secreting cells, increasing nectar production. The adaptive function: a plant that increases nectar concentration in response to bee presence enhances pollinator attraction precisely when pollinators are present. A dynamic response system that optimizes resource allocation to nectar production. Response to wind sounds and mechanical stress: already discussed in the article on thigmotropism (thigmomorphogenesis). Wind produces mechanical vibrations that plants detect and respond to by strengthening their stems. Response to soil vibrations from feeding caterpillars (Appel and Cocroft 2014): already discussed in the bioacoustics article. Vibrations produced by caterpillars are detected by plants and trigger increases in chemical defense. Response to flowing water (Gagliano 2017): corn roots orient toward a silent water source (without VOCs or physical contact). If confirmed, this would suggest a response to acoustic vibrations from moving water.

Mechanisms of vibration perception in plants

Plants detect mechanical vibrations through two main types of mechanisms: direct perception through mechanosensitive channels (already discussed in the touch article) and resonance of leaf or floral structures that amplify environmental vibrations. Petal resonance: plant petals have geometric shapes (bowls, trumpets, bells) with natural resonance frequencies that depend on their shape, mass, and rigidity. In the case of Oenothera (Veits et al.), petals resonate in the bee buzz frequency range. This resonance amplifies vibrations and transmits them to nectar-secreting cells. Transmission through the stem: vibrations applied externally (wind, sound, soil vibration) propagate through stems and roots thanks to the solid structure of plant tissue. Tree stems are excellent conductors of mechanical vibrations (waves propagate at 100–1000 m/s in wood, versus about 340 m/s in air). Frequency discrimination: plant structures have different resonance frequencies that selectively amplify certain frequency ranges. This produces frequency-specific responses even without an "ear" with specialized hair cells. A system of "passive hearing" based on structural resonance and mechanosensitive channels, not on dedicated sensory organs.

Plant bioacoustics: state of the art and controversies

The field of plant bioacoustics is young (less than 20 years of systematic research) and presents several methodological controversies. The most solid findings: ultrasonic acoustic emissions during xylem cavitation (Khait et al., Cell 2023): solidly documented. The response of Oenothera flowers to bee buzzing (Veits et al., Science 2019): published in a high-impact journal, partial replication confirmed. The response of Arabidopsis to caterpillar vibrations (Appel and Cocroft, 2014): published in Oecologia, but independent replication not yet complete. The most controversial findings: corn roots growing toward the sound of water (Gagliano, 2017): not independently replicated. Increased growth with classical music versus heavy metal: not demonstrated under rigorous conditions. Common methodological biases in plant bioacoustics research: difficulty isolating acoustic signals from other signals (soil vibration, VOCs, temperature variations produced by sound sources), absence of standardized protocols between laboratories, tendency to select and publish positive results (publication bias), difficulty replicating due to uncontrolled variables (humidity, temperature, light intensity, soil composition: all influence plant responses). Current consensus: plants perceive mechanical vibrations and some respond to specific frequencies. The existence of a "hearing" system specifically adapted for perceiving biological sounds (pollinators, herbivores, water) has some evidence but requires further verification.

Music and plants: a critical review of the evidence

Many enthusiasts report that playing music to their plants makes them grow better. Scientific research has produced inconsistent results. Studies with positive findings: some studies (mainly from China, India, and South Korea) have shown positive effects of sounds at specific frequencies (mainly 100–500 Hz, both classical music and pure tones) on germination, root growth, and chlorophyll production in certain species. A study by Yonekura et al. (2013) showed that 50 Hz sounds increased flavonoid production in Arabidopsis. Studies with no effects or contradictory results: many well-controlled studies show no significant effects of music on plant growth compared to noisy controls with non-melodic frequencies. Gagliano's meta-analysis (2013, Oecologia) of plant bioacoustics studies found positive effects overall but noted high heterogeneity between studies and possible methodological biases. The control problem: in many studies on "music and plants," the control group is exposed to no sound (silence) rather than non-musical sound at the same intensity. If growth improves in the "music" group, it's unclear whether this is due to the music effect (specific frequencies), vibration itself (general mechanical effect), or heat produced by speakers. Current verdict: some vibrations at specific frequencies (probably in the range of plant cellular structure resonance: 50–500 Hz) may influence specific physiological responses in certain species under certain conditions. The broader claim that "classical music makes plants grow better" is not supported by robust evidence and likely reflects both confirmation bias and publication bias.

Practical applications: acoustic stimulation in agriculture

Despite scientific controversies, some companies and researchers are exploring practical applications of plant bioacoustics in agriculture. Seed germination stimulation with ultrasound: pre-germination treatment of seeds with ultrasonic baths (20–40 kHz, 1–5 minutes). Some research shows accelerated germination and increased germination rate due to seed membrane permeabilization (osmotic and mechanical effects). The mechanism doesn't necessarily require a specific "biological response": cavitation of ultrasound in the soaking liquid can physically open the micropores of the seed coat, facilitating imbibition. Commercial application: some seed treatment companies offer this service, but evidence of large-scale efficacy is limited. Herbivore deterrence with vibrations: vibrations in the frequency range of major flying herbivores (Thysanoptera, aphids, mites: 100–800 Hz) as deterrents. Still in experimental phase. Drought detection with ultrasound: the most promising application. Acoustic emission (AE) sensors applied to plant stems detect xylem cavitation clicks in real time: a non-invasive indicator of water stress that could be integrated into precision irrigation systems. First commercial system in development by Israeli startups (PlantResponse).