How Can Stress Training Increase Yields?

Stress training techniques are cultivation methods that take advantage of the plant's biological features in order to improve or manipulate a crop. Some common and less common stress training techniques include screen of green, monster cropping, FIM-ing, topping, and more. Even pruning is a form of stress induction that benefits the plant. Stress training techniques can be divided into "low-stress training methods" that probably won't kill your crop if they fail, or "high-stress training methods" which are much riskier. Both high and low-stress training methods can increase yields, but how exactly do they do it? If you are extra curious about how plant training methods work, read on.

Botanical Sensory System Overview

Stimulation is sensed from the environment outside the plant.
Signals send messages either around the point of stimulation (local) or further away in other parts of the plant (general).
The part of the plant receiving the signal is prompted by the chemical signal to generate a response to the stimulation.

There are many different scientifically classified responses plants have to various sources of stimulation. Two important types related to increasing growth and yield through stress induction are tropic responses and morphogenesis responses.

Plant Senses: General Mechanisms and Interactions

Despite being incapable of movement from a fixed point in the ground, plants must still find a way to respond to environmental changes and threats. To respond to mechanical stimuli such as touch or herbivory, plants produce "phytohormones" and chemicals that act on genetic traits. Some plants have specialized sensory features like the hairs on the Venus Fly Trap’s leaf, which cause the leaf-trap to close when they are touched. Then there are plants that do not have such specialized sensory features still respond to mechanical stimulation but do so more slowly by changing their appearance (morphology) or growth rate or pattern.

While pruning new growth tips helps branching and budding by re-allocating hormones, pruning dormant branches re-allocates nutrients to the budding parts of the plant resulting in increased bud growth. This is because the plant does not expend the extra energy and nutrients to maintain the un-productive growth, leaving more energy and nutrients to be used by the productive branches and buds. Plants do not have a notable response to thinning, the removal of unwanted growth in dense portions of the plant. Stress training works a lot like pruning in this respect, techniques like topping, tying, and FIM all divert growth hormones from the top of the plant to help the rest of the plant grow more evenly and productively.

How Stress Induction Works to Promote Growth and Yield

Stress training techniques can increase yields, but some extra curious minds may wonder just what goes on inside the plant that creates that result.

Tropic Responses

Tropic responses occur when a plant responds to stimulation by altering growth. The plant may grow towards or away from the stimulus, or in the case of roots, downward. If the source of stimulus is touch, the tropic response is more specifically termed “thigmotropism.” An example of this is when a vine grows to wrap around an object. Directional or spiraling growth involves a process called differential growth, where growth in the area of the plant that contacts the stimulus either slow, accelerates on the side opposite the point of contact, or both.

Morphogenic Responses

Morphogenic response to mechanical stimulus takes place more slowly over time. These responses can strengthen plant tissue and help it cope with stress from repeated force. In general, younger plants have a stronger response than older plants. "Thigmomorphogenesis" is a thickening of the external stem tissue in response to a stimulus such as wind or rubbing on an object. In plants, thigmomorphogenesis can be induced by brushing seedlings flat on a daily basis for their first 2-3 weeks. By emulating wind as a stress source, the plants are induced to grow thicker and shorter stems that are more capable of supporting heavier flower canopies.

Visible Responses of Thigmomorphogenesis

Decreased shoot elongation and increased branching growth
Altered chlorophyll content
Changes to hormone levels
Changes to flowering time
Expression of physiological stress resistance features