By Julie Hullett, Senior Editor, Greenhouse Grower
Greenhouse production is inherently different than field production in many ways and one of the most obvious is the media in which plants are grown. Field crop growers work primarily in natural soils, where managing an ever-changing set of variables from weather to the activity of the soil microbiome is a constant challenge. Greenhouse producers have much more control of their production conditions, but maintaining a healthy growing media — whether soil or soilless— is just as critical.
One area that greenhouse growers are increasingly exploring to encourage healthier soils and healthier plants is the use of biostimulants. Where do these tools fall in the healthy soils/healthy plants conversation?
The Role of Biostimulants
Dr. Michelle Jones, Professor of Horticulture and Crop Sciences at The Ohio State University (OSU), says there are two main claims for biostimulants. First, they can improve or promote plant growth. Second, they can enhance a plant’s abiotic stress tolerance.
“Biostimulants can’t make any claims of disease prevention. They are not biopesticides,” she says. “But if you’re using a biostimulant that can enhance plant growth, you could end up with a healthier plant that is more resistant to disease.”
Jones clarifies that biostimulants also do not replace fertilizer. For example, she says that many growers intentionally inject an excess amount of phosphorus because a lot of it is leached out or becomes unavailable to the plant. Biostimulants can solubilize nutrients and make them more available to the plant. She advises growers to be mindful of the amount of fertilizer that is applied when they are also using biostimulants.
“If your purpose of using biostimulants is growth promotion, if you provide excess fertilizer, then you probably will not see an effect from the biostimulant,” Jones says. “When you reduce fertilizer use, then biostimulants can help ensure those nutrients are used more efficiently. Growers should think about what they want biostimulants to do, and they will need to modify their growing practices to see the full effect.”
Jones advises growers interested in biostimulants to consider the interaction with the host plant. Certain biostimulants maybe be more effective on some crops than others. Her research at OSU focuses on biostimulants with living beneficials. Often an interaction is required between the plant and the microbe for the biostimulant to work effectively. For example, some crops, such as carnations, do not interact with mycorrhizal fungi.
Myths to Dispel
Although biostimulants have a positive impact when used appropriately, some growers remain wary of them. This category of products historically had a reputation in the industry for not always working as intended.
Marie Turner, Director of Scientific Communication at Impello Biosciences, says that there have been ineffective products on the market. When products include living organisms, it is more challenging to keep them functional. Just like plant cultivars, living products perform differently in different environments. A biostimulant that works well in high temperatures may not work as well in a greenhouse with cool-season crops, for instance. Turner says the industry is changing for the better to include more products with proven efficacy and data to back up claims.
“It’s a misconception that biostimulants don’t work. It is true that some of the products don’t work,” Turner says.
James Marlier, Account Manager for Impello Biosciences, advises growers to watch out for false promises.
“You hear a lot about yield increases, and that is a red flag to me. There’s an upper limit to how a variety can perform. You’re trying to reach that limit, but if you’re dealing with different stressors, you’re not going to reach that limit,” Marlier says. “We want to alleviate those stressors so a plant can achieve its maximum result. This isn’t steroids and we’re not trying to push a plant past its abilities. We’re trying to allow the plant to live its best life.”
Some plants are grown with a growing medium like rockwool, Marlier says. In the past, many industry members saw rockwool and similar substrates as sterile. But research shows that plants growing hydroponically have more microbial activity than field soil. Many microbes feed on root exudate, he says.
“Regardless of the growing media, whether it’s soil, soilless, [or] rockwool, there is a lot of organism activity going on around those roots. It’s important to put the good ones in there before the bad ones get a foothold,” Marlier says. “That concept is changing in the industry — hydroponics is not a sterile environment by any stretch of the imagination.”
Experts advise growers to trial biostimulants before incorporating them into production on a large scale, and always work with products with significant data to support their efficacy.
when treated with biostimulants containing phosphate solubilizing bacteria that improve phosphorus uptake by the plants. Plants treated with the biostimulant Lalrise Vita (containing the beneficial bacteria Bacillus velezensis) are larger than control plants with no biostimulant treatment. Photo: Michelle Jones
