Consumer awareness about food safety and environmental sustainability is changing how fruit is produced. Global concern over pesticide residues, deteriorating soil health, and the long-term ecological cost of synthetic agrochemicals has built a steady shift toward safer, greener farming practices. The evidence supports the concern. Prolonged use of synthetic fertilisers and chemical pesticides has been shown to reduce soil microbial diversity, contaminate groundwater, and lower long-term crop productivity (Tilman et al., 2002; Diacono & Montemurro, 2010).
Fruit crops deserve particular attention here. Most are consumed raw after cleaning, without any further cooking, which makes residue-free production especially important. Traditional orchard management has leaned heavily on synthetic inputs for decades, and the health and environmental costs of that reliance are well documented. This is where biostimulants offer a practical alternative. They are substances or microorganisms that, when applied to soil or plant, improve growth, quality, and stress tolerance with far lower ecological impact than conventional chemical inputs (Du Jardin, 2015).
What biostimulants are, and what they do
The word "biostimulant" may sound technical, but the concept is straightforward. These are tools drawn from natural sources that help plants grow better. One of the most widely accepted definitions, from Du Jardin (2015), describes a biostimulant as "any substance or microorganism applied to plants with the aim to enhance nutrition efficiency, abiotic stress tolerance, and/or crop quality traits."
Unlike fertilisers, which directly supply nutrients, biostimulants work by improving the plant's own capacity to absorb and use those nutrients more efficiently. Unlike pesticides, they do not kill pests directly. Instead, they help the plant build resilience and strengthen its defence systems (Calvo et al., 2014). The mode of action varies by product type, but the main pathways include stimulating root architecture and root development, enhancing photosynthetic efficiency and carbon fixation, triggering osmotic adjustment under drought or salinity stress, and increasing the biosynthesis of plant hormones such as auxins, cytokinins, and gibberellins that regulate fruit set and development (Yakhin et al., 2017).
For a broader overview of how biostimulants fit into sustainable production systems, see this practical guide on biostimulants in sustainable agriculture.
Main types of biostimulants
Biostimulants cover a broad family of products that work through distinct biological mechanisms. Du Jardin (2015) grouped them into five main categories, which are still widely used as the reference classification.
Humic and fulvic acids are derived from humified organic matter such as peat, leonardite, lignite, and well-decomposed compost. They act primarily at the root zone, where they improve soil structure, stimulate root development, and chelate micronutrients such as iron, zinc, and manganese. This chelation makes nutrients more available to the plant and is particularly useful on calcareous or alkaline soils where micronutrient availability is often limited.
Seaweed and algal extracts are produced mainly from brown algae such as Ascophyllum nodosum, Ecklonia maxima, and Kappaphycus alvarezii. They contain polysaccharides such as alginates and laminarin, natural phytohormones including cytokinins, auxins, and betaines, and a range of micronutrients. In fruit crops, they are widely used to support flower induction, fruit set, and tolerance to drought, heat, and salinity stress.
Protein hydrolysates and amino acids are obtained through enzymatic or chemical hydrolysis of plant or animal proteins. The resulting mixture of bioactive peptides and free amino acids supports nitrogen metabolism, improves nutrient uptake efficiency, and helps the plant recover from transplant shock, heat stress, or chemical injury. Plant-derived hydrolysates are increasingly preferred in fruit production systems because they avoid concerns around animal-origin residues on edible produce.
Microbial inoculants include plant growth-promoting rhizobacteria (PGPR) such as Azospirillum, Azotobacter, Pseudomonas, and Bacillus, arbuscular mycorrhizal fungi (AMF) such as Rhizophagus and Glomus species, and beneficial fungi such as Trichoderma. These organisms improve nutrient acquisition, particularly of phosphorus through mycorrhizal symbiosis, support root development, and prime plant defence systems against soil-borne pathogens.
Chitosan and silicon-based biostimulants round out the main categories. Chitosan, derived from the deacetylation of chitin in crustacean shells or fungal cell walls, triggers systemic defence responses and helps the plant resist fungal and bacterial pathogens. Silicon-based products strengthen cell walls, improve tolerance to drought and salinity, and have shown particular value in managing physiological disorders in fruit crops when applied alongside calcium.
Examples in fruit crops
Mango. The most economically significant fruit crop in many tropical production systems, mango often suffers from erratic and poor flowering, heavy pre-harvest fruit drop, and inconsistent fruit quality. Research on mango cv. Alphonso has reported that foliar application of seaweed extract liquid fertiliser at 2% concentration during panicle initiation improved panicle length, fruit set percentage, and fruit retention (Prabhu et al., 2018). Similar effects have been documented in mango cv. Kent in Brazil, where biostimulants containing algae extracts improved panicle expansion and fruit retention across consecutive seasons (Lobo et al., 2019).
Banana. Bhattacharya et al. (2015) reported that combined application of Azospirillum and AMF (arbuscular mycorrhizal fungi) inoculants increased bunch weight by around 15% and reduced the incidence of yellowing and early ripening in transit.
Citrus. Protein hydrolysate applications at key phenological stages such as flowering, fruit set, and post-harvest have been reported to improve fruit peel texture, reduce oleocellosis, and increase ascorbic acid content in treated fruit
Apple. Calcium-based biostimulant formulations combined with amino acid carriers have been reported to improve calcium uptake into developing fruit and reduce bitter pit incidence by roughly 30 to 40% in treated orchards.
Application methods
Biostimulants are typically applied in one of three ways. Foliar sprays deliver the product directly to leaves and developing fruit. Soil drenching, often integrated into the irrigation system, applies the product to the root zone. Seed or nursery treatment is used on planting material before transplanting. For established fruit orchards, the most common approaches are foliar sprays and fertigation through the irrigation system (Calvo et al., 2014).
Timing of application
Timing is one of the most important factors in biostimulant performance. For most fruit crops, three stages are particularly critical. The first is pre-flowering and flower initiation, when products that support flower formation and reduce drop can have the largest effect. The second is fruit set and cell division, the window during which cell numbers in the developing fruit are determined. The third is pre-harvest, when quality-oriented biostimulants can support size, colour, firmness, and storage performance.
The global biostimulant market
The commercial picture reflects the scientific trajectory. The global biostimulants market was valued at roughly USD 4.1 billion in 2024 and is expected to continue double-digit annual growth over the next decade, with most forecasts placing the market between USD 8 billion and USD 13 billion by 2030–2034 depending on the source and the methodology used. Europe currently holds the largest regional share, accounting for roughly 38 to 40% of global demand, supported by strong regulatory alignment with sustainable farming goals.
A major policy driver is the European Union's Farm to Fork Strategy, which set a target of reducing the use and risk of chemical pesticides by 50% by 2030, along with a 50% reduction in the use of more hazardous pesticides. Progress toward that target has been mixed, and the legally binding Sustainable Use Regulation that would have enforced it was set aside in early 2024, but the political direction of travel remains clear and continues to shape demand for biostimulants across European fruit production systems.
The future of fruit farming
The combination of consumer demand for safe food, regulatory pressure to reduce synthetic inputs, and the steadily accumulating agronomic evidence for biostimulants points to a structural shift in how fruit crops will be grown over the coming decades, not a passing trend. For fruit growers, biostimulants offer a practical way to reduce input costs, improve fruit quality for premium domestic and export markets, build long-term soil health in perennial orchard systems, and meet the rising consumer and regulatory demand for chemical residue-free fruit.
References
Calvo, P., Nelson, L., & Kloepper, J. W. (2014). Agricultural uses of plant biostimulants. Plant and Soil, 383(1–2), 3–41. https://doi.org/10.1007/s11104-014-2131-8
Diacono, M., & Montemurro, F. (2010). Long-term effects of organic amendments on soil fertility, a review. Agronomy for Sustainable Development, 30(2), 401–422. https://doi.org/10.1051/agro/2009040
Du Jardin, P. (2015). Plant biostimulants, definition, concept, main categories and regulation. Scientia Horticulturae, 196, 3–14. https://doi.org/10.1016/j.scienta.2015.09.021
European Commission. Farm to Fork targets, progress. https://food.ec.europa.eu/plants/pesticides/sustainable-use-pesticides/farm-fork-targets-progress_en
Lobo, J. T., Nunes da Costa, J. R., Moreira, J. N., Cavalcante, Í. H. L., Silva, W. S., Farias, D. B. S., & Souza, I. E. (2019). Biostimulants on nutritional status and fruit production of mango 'Kent' in the Brazilian semiarid region. HortScience, 54(9), 1501–1508.
Tilman, D., Cassman, K. G., Matson, P. A., Naylor, R., & Polasky, S. (2002). Agricultural sustainability and intensive production practices. Nature, 418, 671–677. https://doi.org/10.1038/nature01014
Yakhin, O. I., Lubyanov, A. A., Yakhin, I. A., & Brown, P. H. (2017). Biostimulants in plant science, a global perspective. Frontiers in Plant Science, 7, 2049. https://doi.org/10.3389/fpls.2016.02049