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Melatonin is best known as the hormone that regulates human sleep, stress, and circadian rhythms. But what many growers don’t realise is that melatonin is also produced naturally by plants; and it plays a critical role in growth, stress tolerance, and physiological regulation.
In this blog we explore how melatonin functions in plants, why it’s gaining attention in hydroponics research, and how carefully applied melatonin may act as a powerful biostimulant in controlled growing systems.
Melatonin is a small, naturally occurring molecule derived from the amino acid tryptophan. It’s produced by a wide range of organisms, including:
In humans, melatonin regulates sleep–wake cycles, blood pressure, stress responses, and antioxidant defence. In plants, it serves many surprisingly similar roles.
In plants, melatonin is best described as a signalling molecule, rather than a classical hormone. It acts as:
Importantly, melatonin is produced endogenously (naturally) in plant tissues.
Melatonin is an exceptionally strong antioxidant—around three times more potent than vitamin E.
Its main role is to neutralise reactive oxygen species (ROS), which can damage:
By scavenging these harmful molecules, melatonin protects plant cells during periods of stress.
Melatonin helps plants cope with a wide range of stresses, including:
It interacts with other plant signalling pathways such as:
This makes it particularly interesting for hydroponic and controlled-environment agriculture, where plants are often pushed close to their physiological limits.
Research shows melatonin plays a role in:
It also helps regulate photoperiod responses and circadian rhythms, much like it does in humans.
One reason melatonin is attracting attention in hydroponics is that precise dosing is possible.
Melatonin can be applied as:
Typical application rates fall in the micromolar to millimolar range, meaning accurate measurement is essential.
Because melatonin is water-soluble, it dissolves easily into nutrient solutions, unlike many biostimulants that require solvents or emulsifiers.
Several studies highlight melatonin’s potential benefits:
Tomatoes treated with 50 µM melatonin in hydroponic solution showed:
Lettuce treated with 100 µM melatonin demonstrated:
These effects are indirect; yield improvements come from better stress tolerance, not forced growth.
Melatonin has a very favourable safety profile. It’s widely sold as a human dietary supplement and shows no obvious hazard warnings in agricultural contexts.
Interestingly, melatonin was first identified in plants during studies on coffee, where it was initially thought to be an extraction artefact. Later research confirmed it was naturally produced by the coffee plant itself—meaning your morning coffee contains small amounts of melatonin.
Melatonin is:
When applied carefully, exogenous melatonin may enhance:
For hydroponic growers pushing plants under high-performance conditions, melatonin represents an exciting and scientifically grounded biostimulant option.
Article by Dr Russell Sharp
If you would like to keep up to date with subjects just like this, you can listen to both our podcasts! Links can be found bellow:
Hydroponics Daily Podcast: https://podcasts.apple.com/us/podcast/hydroponics-daily/id1788172771
Cereal Killers Podcast: https://podcasts.apple.com/us/podcast/cereal-killers/id1695783663