A biostimulant is a substance or microorganism applied to plants or the root zone to improve nutrient uptake, efficiency, stress tolerance or quality, independently of its own nutrient content. Common categories are humic and fulvic substances, seaweed and plant extracts, protein hydrolysates and amino acids, chitosan, and beneficial bacteria and fungi. Regulatory definitions differ by jurisdiction.
In practice
Some categories have reasonable evidence in some crops, such as mycorrhizae in low-phosphorus soils and certain seaweed extracts under stress. In cannabis, controlled data are sparse, and effects found so far are small or inconsistent (Evidence: Contested). Results depend heavily on product, dose, medium and cultivar. Growers who want to know should run a side-by-side with an untreated control of the same cultivar.
Don't confuse with
- Fertiliser: supplies nutrients by definition.
- Plant growth regulator: hormone-like substances that directly alter growth, regulated differently.
Myth check
Label claims for biostimulants often run ahead of the evidence. See buyer beware: label claims and Mythbusters.
