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.

What are biostimulants?

A plant biostimulant contains substances and/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. 

Video: Biostimulant basics

  • What are biostimulants?
  • How do biostimulants work?
  • How is the biostimulants market regulated?

For answers to these questions and more, watch the presentation (starts at 5:34:24) filmed at the 2019 AHDB Agronomists' Conference. 

Important considerations before applying biostimulants

  • Some biostimulants are derived from mammalian tissue by-products, including pork and beef material – check that your trade customers or buyers are happy for you to use such materials
  • If using a biostimulant containing microorganisms, consider the environment in which they will be used
  • Carefully follow product labels for time and rate of application. If necessary, consult a professional agronomist

Biostimulant product types

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.

Learn more about the types of biostimulants

How should microbial biostimulants be used?

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

Find out more about how microbial biostimulants should be used

Biostimulants for cereal and oilseed rape crops

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

Learn about using biostimulants on cereal and oilseed rape crops


  • Endomycorrhizal fungus – a type of mycorrhiza, which penetrates the roots of a plant
  • Pathogens – organisms, such as bacteria, viruses and fungi, which are capable of causing disease in other living organisms
  • Polysaccharides – large carbohydrate molecules, such as starch
  • Rhizosphere – the soil immediately next to and influenced by plant roots

Further resources

Information on crop nutrition

Information on soil management