What Are Plant Biostimulants?

Agriculture has always been shaped by change. Shifts in climate, soil health challenges, and the rising cost of inputs are pushing growers to rethink how crops are managed. As these pressures increase, many farmers are looking for tools that improve crop performance without simply adding more fertilizer or chemical inputs.

One category of products attracting increasing attention is plant biostimulants.

Plant biostimulants are substances or microorganisms applied to plants or soils that stimulate natural biological processes, improving nutrient use efficiency, tolerance to environmental stress, crop quality, or nutrient availability. Importantly, these effects occur independently of the product’s nutrient content (Du Jardin, 2015; Rouphael & Colla, 2020).

Rather than feeding plants directly like fertilizers do, biostimulants help plants use available resources more effectively and cope with environmental stress.

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Why Biostimulants Are Gaining Attention

Growers today face a complex set of challenges:

• Increasing drought and temperature extremes

• Soil degradation and nutrient losses

• Rising fertilizer costs

• Pressure to improve sustainability

Biostimulants offer one potential strategy to address these pressures. By influencing plant physiology and soil biology, they can help crops perform more consistently under difficult growing conditions.

Research over the past two decades has shown that biostimulants can influence several important plant processes, including:

• root growth and architecture

• nutrient uptake and nutrient use efficiency

• stress tolerance to drought, heat, and salinity

• plant metabolism and photosynthesis

• crop quality and yield stability

These effects have led to rapid growth in the biostimulant sector worldwide.

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How Biostimulants Work

Biostimulants do not function through a single mechanism. Instead, they influence several interconnected biological processes within plants and the surrounding soil environment.

Some biostimulants enhance root development, allowing plants to explore a greater volume of soil for water and nutrients. Others influence plant hormone signaling, activating natural growth pathways or improving stress tolerance.

Certain microbial biostimulants interact directly with the rhizosphere — the zone of soil surrounding plant roots where microbes and plant exudates interact. These microorganisms can help mobilize nutrients, improve nutrient cycling, or stimulate root growth.

Other biostimulants function through biochemical signaling, activating antioxidant systems or helping plants regulate stress responses during drought, heat, or salinity.

Because of these diverse mechanisms, biostimulants are best understood not as a single type of product but as a broad category of inputs that support plant performance through biological processes.

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Major Categories of Biostimulants

Although the category is diverse, several major groups of biostimulants are widely recognized.

Microbial Biostimulants

Beneficial microorganisms such as Bacillus, Pseudomonas, and mycorrhizal fungi are commonly used as microbial inoculants. These microbes can enhance nutrient availability, improve root development, and support plant resilience under stress.

Humic and Fulvic Substances

Humic substances form naturally during the decomposition of plant and microbial material in soils. These complex organic molecules influence soil chemistry, nutrient availability, and root growth.

Seaweed and Plant Extracts

Seaweed extracts — particularly those derived from brown algae such as Ascophyllum nodosum — contain a mixture of bioactive compounds that can influence plant metabolism and stress tolerance.

Protein Hydrolysates and Amino Acids

Derived from plant or animal proteins, these products supply peptides and amino acids that influence plant metabolism and nitrogen assimilation.

Biopolymers

Certain natural polymers such as chitosan act as signaling molecules that stimulate plant defense responses and improve tolerance to environmental stresses.

Beneficial Elements

Some elements not traditionally considered essential nutrients — including silicon, cobalt, and selenium — can improve plant resilience and nutrient efficiency under certain conditions.

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What the Research Shows

Scientific interest in plant biostimulants has increased dramatically in recent decades. Hundreds of peer-reviewed studies now explore how these products influence plant physiology, soil biology, and crop productivity.

A widely cited review by Calvo et al. (2014) summarized growing evidence that biostimulants can enhance root development, nutrient uptake, and tolerance to abiotic stresses. Later research has expanded our understanding of how biostimulants influence plant hormonal signaling, antioxidant activity, and microbial interactions in the rhizosphere.

Microbial biostimulants in particular have been studied extensively for their ability to improve nutrient cycling and nutrient use efficiency. Beneficial rhizobacteria can help mobilize phosphorus, fix atmospheric nitrogen, and stimulate root growth, improving the plant’s ability to acquire nutrients from soil (Backer et al., 2018).

Seaweed extracts, humic substances, and protein hydrolysates have also shown measurable effects on crop growth and stress tolerance across a wide range of crops.

While results vary depending on soil conditions, climate, and crop species, the overall body of research suggests that biostimulants can play a valuable role in improving agricultural resilience.

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Biostimulants and the Future of Agriculture

Global agriculture faces a difficult balancing act: producing more food while protecting soil health, water resources, and the long-term sustainability of farming systems.

Biostimulants are not a replacement for fertilizers or sound agronomic management. Instead, they represent a complementary tool that can help growers improve the efficiency of existing inputs and reduce vulnerability to environmental stress.

As research continues to uncover the biological mechanisms behind these products, biostimulants are likely to play an increasingly important role in modern crop production systems.

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References

Backer, R. et al. (2018). Plant growth-promoting rhizobacteria: mechanisms and commercialization. Frontiers in Plant Science.

Calvo, P., Nelson, L., & Kloepper, J. (2014). Agricultural uses of plant biostimulants. Plant and Soil.

Du Jardin, P. (2015). Plant biostimulants: definition and concept. Scientia Horticulturae.

Rouphael, Y. & Colla, G. (2020). Biostimulants in agriculture. Frontiers in Plant Science.

Yakhin, O. et al. (2017). Biostimulants in plant science. Frontiers in Plant Science.