Biostimulants Part 1: What Are They and What Can They Do?

Ontario greenhouse growers are increasingly experimenting with biostimulants to potentially boost plant quality. Used correctly, these products could help cut fertilizer costs, improve stress tolerance, and enhance overall crop quality.

However, using these products without the knowledge of different categories of biostimulants, and sufficient in house trialing, can waste your time and money.

In this first post of this two-part series, we will discuss what biostimulants are, the different categories they fall into, and first steps for choosing a product to trial. In the second post (coming soon!), we’ll discuss important tips for choosing a biostimulant, as well as potential drawbacks and, most importantly, how to trial this on your own farm for YOUR crop.

Only looking for certain information? Use the table of contents to navigate between sections.

1. Biostimulants Explained
   1. What they do:
   2. Potential Benefits:
2. Biostimulant Active Ingredients
3. Understanding Categories of Biological Products
4. First Steps for Choosing a Product

Biostimulants Explained

What they do:

Biostimulants are products designed to boost natural plant processes, helping crops take up nutrients more efficiently, tolerate stress, and improve overall quality and yield. But how do they actually do that?

There are several ways that various biostimulants can potentially achieve these results. One way is by stimulating the plant to produce more growth-promoting hormones that may increase shoot, leaf or root growth. For example, hormones – like auxins – can promote root growth, increasing efficiency of water use and nutrient uptake through the roots.

Another major mechanism is improving nutrient availability in the growing media. Instead of letting nutrients get locked up or leached away, biostimulants can help solubilize them for plants to absorb more easily.

Potential Benefits:

There are various benefits to using biostimulants depending on what product you choose, the crop you’re growing and its stage of growth when you apply the product. See Figure 1 for a breakdown of potential benefits at different stages of production.

Figure 1. Potential benefits of biostimulants during different stages
of production. Figure taken from Nathan Nordstedt.

The largest and most exciting benefit for growers that I see coming out of recent research is the potential to significantly reduce fertilizer inputs. With spring crops on the horizon, many farms will soon start burning through the fertilizer to produce those vigorous spring crops we all love to buy (and then kill) for our patios.

A recent study conducted by Ohio State University found that applying biostimulant treatments to pansies improved plant growth when fertilizer rates were reduced by 50%, down to 75 ppm (see Figure 2). For the beneficial bacteria-based product, they applied a biofungicide called Cease weekly; this product also contains biostimulant ingredients. MycoApply Endo was incorporated into the media as the beneficial fungi-based product.

For more information on research from Ohio State University, check out the American Floral Endowment’s recent webinar on biostimulants for floriculture production.

Figure 2. Growth responses of biostimulant treated pansies when grown under varying nitrogen fertilizer rates (15-5-15). Figure taken from Laura Chapin

Biostimulant Active Ingredients

The active ingredients used in biostimulants fall into two major categories: microbial and nonmicrobial, as seen in tables 1 and 2. Often, a product will include many types of bacteria or fungi or a mix of active ingredients from different categories.

Some of the product examples in Table 1 and 2 are not solely biostimulant products because they contain nutrients (*) or they make pest/disease control claims (**). We will dive into this distinction in the next section of this post.

Table 1. Microbial Biostimulant Active Ingredients

Type of active ingredient	Active ingredient examples	Product examples (not exhaustive)
Beneficial Microorganisms	Bacteria: Bacillus, Pseudomonas, Rhizobium Fungi: Endomycorrhizae, Ectomycorrhizae, Trichoderma	– Earth Alive Soil Activator – Era Boost Pro – LalRise MAX WP – Rootshield (various formulations)** – Rhapsody** – Trianum-P** – Microflora PRO
Humic Substances	Humic acid Fulvic acid	– EZ-Gro 0-0-3 Fulvic Acid* – EZ-Gro 0-0-5 Humic Acid*

Table 2. Nonmicrobial biostimulants

Type of active ingredient	Active ingredient examples	Product examples (not exhaustive)
Protein hydrolysates	Animal or plant-derived amino acids	– On-Gard* – LalStim OSMO
Biopolymers	Chitosan Laminarin	– Crustacean Meal 5-2-0* – EZ-Gro Chitosan
Botanical extracts	Algae Brown seaweed Other plant extracts	– OHM Biostimulant*

Understanding Categories of Biological Products

Biofertilizers and biofungicides are additional biological crop products that tend to muddle our understanding of “biostimulants” even more.

Technically, a biostimulant product does not contain added nutrients or make any pest/disease control claims — it’s meant to stimulate natural processes, not feed the plant directly. However, many products on the market include small amounts of nutrients alongside biostimulant active ingredients and are therefore labelled as “fertilizers.” In these cases, the product falls under Canada’s fertilizer regulatory system, meaning it has a valid Fertilizer Registration Number — this number simply verifies that the product meets federal standards.

Similarly, some products include biostimulant ingredients but are labelled as “fungicides” and given a PCP number after meeting PMRA requirements and demonstrating real disease‑control efficacy. If a product label claims that the product can help control diseases, but it doesn’t have a PCP number, then this claim cannot be verified.

Biofertilizers, biofungicides, and biostimulants can have similar growth promoting effects on crops. This makes it tougher for growers to identify and trial products containing biostimulant active ingredients. Even if a product is labelled for nutrients or pest/disease control, it may also contribute to plant stress tolerance, improved rooting, or better nutrient uptake.

**Note: If a product is registered with PMRA you must follow the label. This means you must use the product for the pests/diseases it is labelled for. Any added growth promotion benefit is a bonus.

Table 3. Regulatory Categories of Biological Products

	Biostimulant	Biofungicide	Biofertilizer
Possible Biostimulating Ingredients	Contains any of the active ingredient types listed in tables 1 & 2	Typically contains microbial ingredients listed in the “Beneficial Microorganisms” row in table 1. May include others as well.	Typically contains non-microbial ingredients listed in table 2 or humic substances from table 1.
Claims on the label	Claims to increase one or more of the following: nutrient efficiency, stress tolerance, overall quality, yield, etc. May make pest or disease control claims that have not been verified by PMRA.	Must make claims to control fungal plant diseases. These claims are verified through PRMA registration. May also make claims to increase one or more of the following: nutrient efficiency, stress tolerance, overall quality, yield, etc.	Includes a valid Fertilizer Registration Number. May also make claims to increase one or more of the following: nutrient efficiency, stress tolerance, overall quality, yield, etc.
Registration Status	No registration	Registered with PMRA and has a unique PCP number.	Registered under the fertilizer act with a unique fertilizer registration number

First Steps for Choosing a Product

So how do you sort through all these options and choose something worth trialing on your farm? Here are the first steps.

Before you even start comparing products, it’s essential to decide what your goal is and what you plan to measure. Are you hoping to reduce plant stress? Improve rooting? Cut fertilizer inputs? Reduce disease pressure? Your end goal determines which product category you should start with.

If you’re specifically interested in testing biostimulant products, the label is your best friend—check whether it includes nutrients (which would make it a fertilizer) or pest‑control claims (which would make it a biofungicide). That said, don’t automatically rule out biofertilizers or biofungicides; many of these products contain the same active ingredients found in biostimulants and can offer equally strong biostimulant effects depending on your objective. The key is simply knowing what you’re testing and why, rather than getting hung up on the label category.

For example, if your goal is to manage a specific pest or disease issue—like root rot—your starting point should always be a registered biofungicide, since it’s the only category that has been tested and approved to control those problems. But if your goal is to improve plant quality, reduce fertilizer inputs, or help crops tolerate stress, you have much more flexibility: effective products may come from the biostimulant or the biofertilizer category. The important part is matching the product to your objective so that your trial actually answers the question you care about (more on how to design that trial in the next post!).