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Be A Better Gardener: New developments in biostimulants

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By Thomas Christopher

For Capital Region Independent Media

What can biostimulants do for your garden? File photo

I’ve been gardening for more than half a century, long enough to be skeptical about the latest horticultural miracle cures.

Generally, I find more success in overcoming gardening problems by applying time-tested techniques of good cultivation. Nevertheless, I am excited by what I am learning about biostimulants.

What are biostimulants? They are any substance or microorganism that may be applied to plants or to the soil around them that can invigorate the growth of the plant and/or enhance its ability to react effectively to environmental stress. Their use, I learned in the course of a recent conversation with Dr. Matthew Kleinhenz of The Ohio State University, can date back millennia.

Seaweed, for example, has been gathered in coastal areas as fertilizer for farm crops as early as the days of ancient Rome, and its use became widespread by the mid-12th century throughout coastal Europe.

Turned into compost or applied directly to the soil, seaweed boosts the soil’s organic content and adds a rich menu of minerals and plant nutrients. Seaweed and seaweed extracts also supply amino acids, plant hormones, and other compounds that promote seed germination, plant rooting and growth, and improve the quality of fruits and vegetables while increasing harvest size. Substances found in seaweed have also proven effective at enhancing plants’ ability to deal with drought, cold, and disease.

We hear a lot currently about climate change, and few gardeners I meet, no matter what their political beliefs, will deny that in their experience the local climate is different now than years ago. But my wife the environmental scientist prefers to refer to this process not as “climate change,” but rather as “climate chaos.” That’s because the overall heating of our environment has upset the mechanisms that used to moderate the local weather so now we are experiencing frequent anomalies such as record rains and floods, alternating with more frequent and severe droughts, and uncommonly late spring frosts coupled with more intense and sustained heatwaves.

I find my garden struggling as a result. That’s why I contacted Dr. Kleinhenz, whose work involves research into new biostimulants and working with vegetable growers to successfully incorporate their use into their cultural regimes. He is especially interested in the relatively new usage of naturally occurring microbes – bacteria and fungi – as biostimulants.

I shared some concerns with Dr. Kleinhenz. Would the application of these new biostimulants damage the local ecology? He replied that he and his colleagues have not found that to be the case. Indeed, because the microbes used were initially found in the soil and habitat, they are even approved for use in organic agriculture by OMRI, the Organic Materials Review Institute, an independent non-profit that verifies that products proposed for use in organic agriculture meet all the relevant, internationally recognized standards.

Examples of microbial biostimulants may also sometimes have a long pedigree. Those legume inoculant powders sold at garden centers and by mail order have been used for more than a century to enhance the growth of beans and peas. These inoculants enhance the growth of the target plants by supplying strains of rhizobia bacteria that form an association with the plant roots, converting atmospheric nitrogen into forms of nitrates the plants use to promote growth. By reducing the need for nitrate fertilizers, the inoculants reduce inputs needed for raising the crop, in particular, the fossil fuels used to produce synthetic fertilizers.

The bacteria in these inoculants are just a few examples of what has become a burgeoning field of research. PGPB’s – “plant growth promoting bacteria” – cannot only partner with plants to produce nitrates but also help protect them against soil-borne pathogens, produce hormones that boost plant growth and emit compounds that enhance plant resistance to insect pests and bacterial pathogens.

Applications of beneficial fungi can greatly extend the reach of plant roots, increasing plants’ ability to absorb water and nutrients from the soil, enabling them to flourish despite drought and soil deficiencies. Other fungal biostimulants can promote root growth and branching and protect against fungal diseases.

For recommendations of specific products and biostimulants appropriate for your particular plants, soil and region, Dr. Kleinhenz recommended consulting your local Cooperative Extension service, which is typically headquartered at your state’s land-grant university. As the stresses on our gardens increase, who can ignore such a promising new (and old) tool for plant enhancement?

To listen to my conversation with Dr. Kleinhenz, log on to the Berkshire Botanical Garden’s “Growing Greener” podcast at www.berkshirebotanical.org.

Be-a-Better-Gardener is a community service of Berkshire Botanical Garden, located in Stockbridge, Mass. Its mission, to provide knowledge of gardening and the environment through a diverse range of classes and programs, informs and inspires thousands of students and visitors each year. Thomas Christopher is a volunteer at Berkshire Botanical Garden and is the author or co-author of more than a dozen books, including Nature into Art and The Gardens of Wave Hill (Timber Press, 2019). He is the 2021 Garden Club of America’s National Medalist for Literature, a distinction reserved to recognize those who have left a profound and lasting impact on issues that are most important to the GCA. Christopher’s companion broadcast to this column, Growing Greener, streams on WESUFM.org, Pacifica Radio and NPR and is available at berkshirebotanical.org/growinggreener.

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