PHOTO: Connie Ma/Flickr
Karen Lanier
March 27, 2017

Whether on a farm or out in the wilderness, stress is a part of life. All organisms—including both plants and humans—strive for homeostasis, which is not a static state of perfect balance, but rather a continuum of ebbs and flows, gives and takes, and pushes and pulls that make up the necessary dance steps for survival at every level of life. In small-scale organic farming, moderate stress on plants plays an important role just as it does in natural ecosystems.

Plants Have Options

When disease or another hard time hits, plants can react in a few different ways: adapt, avoid or die. They might develop resistance by becoming acclimated to growing and surviving despite the setback, or they might be susceptible and eventually die or fail to produce viable seeds. They can also escape the stress by simply avoiding it—a beneficial quality for ephemeral, short-lived plants.

This third option, stress avoidance, is what many desert and arctic plants employ to survive. With very short growing seasons, they maximize moisture and temperature opportunities to mature, bloom and set seed quickly. Those seeds can lie dormant for many years, escaping potential threats until the right growing conditions happen again.

Plants Can Learn

Monica Gagliano, researcher at the University of Western Australia, and her colleagues are making waves in the field of plant cognition. They have proven that plants are intelligent and can learn how to adapt to repetitive stress. The key word here is learn, not just survive once and get by on luck. Just as we look back at stressful situations and ask ourselves, “Now, what did I learn from that so I can be better prepared next time?” Gagliano’s experiment with the sensitive plant (Mimosa pudica) shows that this plant can’t be fooled too many times.

The sensitive plant’s stress response is to close its leaves, presumably to look wilted and unappealing to a predator and to conserve photosynthesizing energy. After a series of controlled drops that induced the closed-leaf stress response, the plant stopped reacting. The sensitive plant became acclimated and somehow knew that it would survive the next drop, so there was no need to protect itself from danger. This is an example of a plant adapting to stress, which is easily reversed without changing anything in its genetic structure.

Hardy Plants

Over time, if plants are exposed to similar stresses and their entire population acclimates, the next generation inherits this change and has a greater likelihood of survival. This is where the term hardy comes in, meaning the variety of the plant has an increased capacity for resilience despite environmental changes, such as cold winters. There are a wide range of ways that plants acclimate to stresses, including changing their leaf size, developing antifreeze or heat-shock proteins, or adjusting the ions in their cells to compensate for dry soil.  

Hormonal shifts in plants are another way that they deal with stress—this is also seen in humans—but in plants, different chemicals are emitted from different pores, depending on the stressor. Beneficial insects could be called in to attack a pest by these subtle yet powerful cues. Volatile organic compounds in the smell of freshly-cut grass is a familiar example of an aromatic cry for help.

How Do You Stress Your Plants?

Many gardeners swear by stressing certain plants in certain ways to achieve a desired effect. Letting peppers wilt before watering them is supposed to make them hotter. Forcing tomato plants to flower and set fruit by keeping them confined to a pot is another common practice. Coppicing and pruning could be considered intentional stresses, as well, by redirecting energy to new growth elsewhere. 

Don’t view all stress as harmful to plants. Drought, flood, pests, cold snaps—these events that disrupt homeostasis are a catalyst for change. In the right doses, plants and the gardens where they live can turn this discomfort into growth and long-term stability.

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