Low-Stress Training (LST) is a cultivation technique that physically manipulates a plant’s structure to optimize light exposure and manage the overall canopy shape. LST encourages lateral growth, maximizing the efficiency of light sources and leading to a uniform distribution of energy across the plant. Successful implementation relies heavily on precise timing, especially for photoperiod plants whose life cycles are governed by light exposure. Understanding the plant’s growth phases is essential for beginning this process at the correct moment to ensure the best results.
Defining Low-Stress Training and Photoperiod Stages
Low-Stress Training involves gently bending and securing the main stem and branches to force a horizontal growth pattern without causing significant damage. This technique differs from High-Stress Training (HST) methods, such as topping or heavy pruning, which inflict larger wounds. LST is preferred because it avoids the recovery time associated with more invasive procedures, ensuring continuous growth.
Photoperiod plants have two main life stages controlled by daily light exposure. The vegetative phase focuses on developing roots, stems, and foliage, requiring a long light cycle of typically 18 or more hours per day. The flowering phase is triggered when light hours are reduced to a shorter cycle, commonly 12 hours of light and 12 hours of darkness. LST must be performed entirely during the vegetative stage, as this is when the plant actively grows the structure that will support flower production.
Optimal Timing for Initiating LST
The most opportune moment to begin LST is during the early vegetative stage, after the plant has established a robust root system. A plant is ready for its first bend when it has developed a minimum of three to five true nodes, which are the points on the stem where branches and leaves grow out. Starting too early, before the third node, is detrimental because the young plant lacks the necessary stability. Conversely, waiting too long causes the main stem to lignify, making it difficult to bend without causing severe stress. The soft, pliable new growth found in the early vegetative phase is flexible enough to be easily manipulated.
The primary goal of LST is to interrupt apical dominance, where the main stem grows vertically and suppresses lower branches. Bending the main stem over removes the apical meristem as the highest point, causing growth hormones (auxins) to redistribute across lower growth sites. This encourages auxiliary branches to grow upward and become new main flower sites, creating a wide, flat canopy that receives equal light exposure. Training must be completed well before the shift to the flowering photoperiod.
Essential Techniques for Applying LST
Applying LST requires only a few basic, gentle materials to secure the branches into their new positions. Soft plant ties, rubber-coated wire, or specialized LST clips are ideal because they will not cut into the stems as the plant grows. Thin wire or standard string should be avoided, as they pose a high risk of girdling or damaging the living tissue.
The technique begins by gently bending the main stem horizontally and securing it to the edge of the pot or a stake using soft ties. This initial bend immediately redirects the plant’s energy to the side branches. As the side branches grow upward toward the light source, they must also be gently bent and tied down to maintain the flat canopy.
LST is a continuous process of observation and adjustment throughout the vegetative phase, not a one-time event. Ties must be regularly monitored and repositioned to prevent them from digging into the expanding stem. The ongoing goal is to keep all growing tips at a similar height, ensuring light penetrates deep into the canopy and promotes numerous, evenly-sized flower sites.
Adjusting LST During the Flowering Transition
Minor adjustments may be necessary during the initial transition into flowering, even though LST is primarily a vegetative technique. When photoperiod plants switch to a 12/12 light schedule, they undergo a rapid growth spurt known as the “flowering stretch,” lasting one to two weeks. During this phase, the plant can significantly increase in height, potentially disrupting the established canopy structure.
It is appropriate to continue securing rapidly stretching branches during this initial period to maintain an even canopy height. However, once the plant stops vertical growth and focuses on bud development, all physical training must cease. Applying LST deep into the flowering phase causes undue stress, potentially hindering flower production.
The structure established during the vegetative phase must be maintained, but aggressive manipulation should be avoided after the third week of the 12/12 cycle. Later adjustments should be limited to securing heavy, developing flower clusters with stakes or supports to prevent snapping. The focus shifts entirely from shaping the plant to supporting the flower mass.