Plant biostimulants: Function and efficacy

Numerous microbial and non-microbial substances claim to benefit your crops. Our research-based guidance cuts through the noise to help you identify the biostimulants most likely to deliver results.

A plant biostimulant contains substances or microorganisms that stimulate natural plant processes.

The effect will be independent of its nutrient content and will improve one or more of the following characteristics of the plant or the plant rhizosphere:

• Nutrient-use efficiency
• Tolerance to environmental stress
• Quality traits
• Availability of nutrients in the soil or rhizosphere

The main role of a biostimulant should not be to provide fertilisation or pesticidal activity. Any product marketed as a pesticide must have a Ministerially Approved Pesticide Product (MAPP) number. 

In the UK, a diverse range of biostimulants are available. These are grouped as either ‘microbial’ or ‘non-microbial’ and can be further classified by product type.

Microbial biostimulants contain living organisms and require careful management both before, during and after application. Management will vary depending on the organism in question.

AHDB has reviewed the evidence on the efficacy of biostimulants used on cereal and oilseed rape crops.

Baffled by biologicals, such as biostimulants and biopesticides?

This autumn and winter, 2026 to 2027, join farmers, AHDB, the Voluntary Initiative and ADAS experts to explore the science, evidence and practical considerations associated with using biologicals in commercial cereal and oilseed systems.

Our roadshow, which will see 11 in-person events take place across the UK, will explore where biologicals can realistically deliver and where the evidence is still limited or uncertain.

It won’t tell which products to buy, but it will give you the knowledge and confidence to decide whether, when and where a biological has a place on your farm.