What biostimulants actually do

Until recently, biostimulants were sold as fertilizers, or as something in between a fertilizer and a pesticide, and a grower could rarely be sure what was really in the bottle. That changed in July 2022, when the European Union began recognizing them as a distinct category of plant nutrition products under Regulation (EU) 2019/1009, the first regulator in the world to do so. The law defines them by what they do rather than what they contain. A biostimulant stimulates the plant's own processes, regardless of its nutrient content, to improve nutrient use efficiency, tolerance to abiotic stress, quality traits, or the availability of nutrients in the rhizosphere.

A fertilizer feeds the crop, and a plant protection product targets a pest. A biostimulant works on the plant itself, helping it use water and nutrients more efficiently and hold its ground when conditions turn against it.

The three types and when to reach for each

Most products on the shelf fall into one of three groups, and they are not interchangeable.

Seaweed extracts, usually from Ascophyllum nodosum and similar brown algae, carry natural growth regulators such as cytokinins and betaines along with alginates and trace elements. They are the usual choice around stress, whether that means transplanting, flowering and fruit set in heat, or a dry spell, when they help the plant keep growing roots and setting fruit instead of stalling.

Amino acids and peptides are the building blocks of protein, supplied in a form the plant can take up directly. Producing them from scratch costs the plant energy, so supplying them ready-made helps most at high-demand moments such as early growth, fruit fill, and recovery after frost, hail, or pest damage. Many products in this group also chelate micronutrients, which improves the uptake of iron, zinc, and manganese.

Humic and fulvic acids work mainly in the soil and on the roots rather than on the canopy. They improve soil structure, hold nutrients in the root zone, and encourage finer root growth, which is why growers often apply them early and through the irrigation to get a crop established on poor or tired soils.

Where biostimulants help most

Biostimulants do most of their work when the plant is under stress, which is the opposite of how the label usually sells them. On a well-watered, well-fed crop in a good season, the measurable response is often small. Push the same crop into drought, heat during fruit set, salinity, or transplant shock, and the gap between treated and untreated plants opens up.

In controlled trials on stressed plants, seaweed-based products have increased tomato yields by as much as 70% compared with untreated plants under the same stress. That 70% is the difference between treated and untreated plants once the stress has hit, so it measures how much yield the product protects when conditions turn bad, rather than extra yield on a crop that was already thriving. The same review is blunt about how far results move from one product to the next, partly because the raw material varies, especially seaweed harvested from the wild, where the species, the harvest season, and the processing all change what ends up in the bottle.

A biostimulant behaves more like insurance than like fertilizer. It earns its place when you apply it ahead of a stress you can see coming, such as before a heatwave, around transplanting, or going into a dry spell. What should guide your decision is the trial data for your own crop and conditions, since a headline percentage only describes what happened in one trial on someone else's field.

How to compare cost per application

Two products at the same shelf price can cost very different amounts to use. What you actually pay per hectare depends on the price per litre or kilo together with the dose the label calls for, so a cheaper bottle applied at a heavy rate can end up dearer than a concentrated one used sparingly. Working out that cost per application before you order is what tells you which product is genuinely cheaper.

On Farmclick, you can see products from different suppliers side by side, with their prices, so you can work out the real cost before you order. Farmclick is the first digital B2B marketplace for agricultural inputs in Greece, a joint initiative of Piraeus Bank and Wikifarmer that brings suppliers from across the country together with nationwide delivery. Through Piraeus Bank financing, you can source your inputs now and align payment with your crop cycle, which helps when nutrition costs come before harvest revenue.

See all biostimulants and compare prices, or browse seaweed extracts, amino acids and humic and fulvic acids on their own.