By Kristen Hampshire
Biostimulants can help plants better absorb nutrients, deal with stress, and even improve yields.
They stoke fertilizer uptake and can help plants power through drought. Some improve pest and disease resistance, others stimulate plants’ natural processes, so they simply do a better job of using nutrients. In a lot of ways, biostimulants are like vitamins — not medicine. They can make plants more resilient, less susceptible to abiotic stress, and more likely to recover after wilting on the shelf. But they’re not a be-all-end-all.
Technically, plant biostimulants contain substances and/or micro-organisms whose function when applied to plants or the rhizosphere is to simulate natural processes to enhance/benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, and crop quality (European Biostimulants Industry Council).
“Biostimulants give us a whole new suite of tools to improve plant performance and plant stress-resistance,” says Neil Mattson, associate professor, plant science at Cornell University.
Biostimulants are not fertilizer. They are not pesticides, even if some will increase plants’ resistance to harmful insects. Rather, biostimulants improve the way these inputs work.
“If we look at a biostimulant that is making fertilizer uptake more efficient, then that would not be applied in place of a fertilizer but in combination with it,” Mattson explains. “You could reduce the amount of fertilizer you add to some degree because you added a product that helps the plant take it up.”
Mattson refers to biostimulants as “another tool in the toolkit to make healthier plants that are more tolerant.” And, considering the range of stressors plants face at every stage in their lifecycles, a little extra protection is positive for growers, greenhouse businesses, and consumers, who might have better success at home with a plant treated with biostimulants.
Application depends on the type of biostimulant, and Mattson identifies seven main categories:
■ Humic and fulvic acids
■ Protein hydrolsates and other nitrogen-containing compounds
■ Seaweed extracts and botanicals
■ Chitosan and other biopolymers
■ Inorganic compounds
■ Beneficial fungi
■ Beneficial bacteria
Some biostimulants are applied as a foliar spray, and others are watered into the plant root zone.
“Sometimes, repeat applications may be required,” Mattson says. “Growers should read labels carefully to determine the proper timing, rate, and application method before using any biostimulant.”
Mattson has tested a number of biostimulants to observe their impact on plant health. One included the application of potassium silicate (56 ppm in CLF) to poinsettias, 12 days post-harvest. The plant that received a biostimulant application showed a marked improvement in vitality and overall appearance.
In another test, potassium silicate (silicon) was applied to plants that were then put into a controlled-drought stress environment of 102°F. After three and 4½ days, the plant receiving silicon was obviously healthier by its appearance. For this test, the plant received a 10 mL/L weekly drench.
“The addition of silicon to greenhouse plants growing in soilless substrates appears to be beneficial for certain plants under certain conditions,” Mattson reports. Those conditions include: a present stressor like heat, salt, or biotic; and when the tap water, fertilizer, or substrate does not continually supply enough silicon as a contaminant. Also, he adds, “Silicon is not a miracle cure for every stress.”
Create a Control Plot
Control plots are necessary so growers can compare crops treated with biostimulants with those that did not receive applications, Mattson says. “Consider environmental factors that may or may not lead to observed benefits,” he adds.
And, keep records.
“Biostimulants are a large class of materials,” Mattson says, adding that this can make them intimidating to some growers. But the potential for biostimulants to boost plant health and address issues like pest and disease resistance is promising, and growers are seeking new strategies for dealing with these issues.
“Biostimulants are appealing to growers who are quite proactive at looking for ways to replace conventional controls,” Mattson says.