The flowering stretch is a rapid growth phase that occurs as a plant transitions from its vegetative stage to the reproductive stage. Understanding this period is important for growers to manage vertical space, especially in indoor environments where height is limited. This sudden burst of vertical growth is a natural part of the plant’s life cycle, signaling a shift in its biological priorities.
Understanding the Flowering Stretch Phenomenon
The flowering stretch is defined by a rapid, often dramatic increase in the distance between the plant’s nodes, resulting in greater vertical height. This phenomenon is a direct result of hormonal changes within the plant, specifically an increase in growth-promoting hormones like gibberellins and auxins. Gibberellins act as growth accelerators, causing both cell division and cell stretching.
The biological purpose of this intense upward growth is to position the plant for optimal light capture and improved air circulation before the dense flower structures develop. By quickly increasing its height, the plant maximizes light exposure across its canopy. This also helps to spread out the developing flower sites, which aids in preventing mold and mildew accumulation from poor airflow.
The Typical Timeline for Stretch Initiation
For photoperiod-dependent plants, the stretch phase is initiated when the light cycle is switched from a long-day (vegetative) schedule to a short-day (flowering) schedule, typically 12 hours of light and 12 hours of darkness. The first signs of rapid vertical growth usually begin within the first week after this light cycle change.
The most intense period of growth occurs between weeks two and three of the flowering cycle. During this time, the plant can significantly increase its height, often doubling or even tripling its size depending on the strain. This initial growth spurt typically concludes by the end of the fourth week of flowering, after which the plant focuses its energy primarily on flower and bud development.
Genetic and Environmental Influences on Stretch
The exact timing and magnitude of the flowering stretch are highly variable, largely determined by the plant’s genetics and its surrounding environment. Sativa-dominant strains are genetically predisposed to stretch significantly more and for a longer duration compared to Indica-dominant strains. A Sativa may easily double or triple its height during the stretch, while a compact Indica may only increase by 50 to 100%.
Environmental factors also play a major role in regulating the stretch. The light spectrum is a notable influence, as light with a higher proportion of red light can promote stem elongation, while blue light tends to encourage shorter internodal spacing and more compact growth. Temperature differential between day and night is another factor, as a large difference can promote the production of gibberellins, leading to greater vertical growth.
The intensity of the light is also a regulator, as plants stretch aggressively in low light conditions, a process known as etiolation, to search for a stronger light source. Ensuring adequate light intensity and proper distance from the light fixture can help mitigate excessive stretching.
Practical Methods for Height Management
Growers must proactively manage the stretch to prevent plants from growing too close to the lights, which can cause heat stress and light burn. One common technique is Low-Stress Training (LST), which involves gently bending and tying down the main stems and branches to encourage a more horizontal canopy. This method directs the vertical energy into lateral growth, better utilizing the available space.
More aggressive High-Stress Training (HST) techniques are also employed, such as super cropping, which involves crushing and bending the stem to redirect growth and create a more level canopy. Utilizing a screen, often referred to as the Screen of Green (SCROG) method, is highly effective, as it forces the branches to grow horizontally and fill the entire area under the light.
Adjusting environmental conditions can also curb excessive vertical growth. Lowering the night temperature to minimize the day-to-night temperature differential can reduce gibberellin production. Additionally, some growers will reduce the nitrogen levels in their nutrient solution during the early flowering phase to discourage vegetative growth and promote a more compact structure.