When growing photoperiod-sensitive plants indoors, “flipping to flower” is the transition from the vegetative light cycle (typically 18/6) to the flowering light cycle (12 hours of light and 12 hours of uninterrupted darkness). This deliberate change signals the plant to enter its reproductive phase. Managing this transition controls the final size of the plant, especially its vertical growth, ensuring it does not outgrow the available space or suffer light burn against the lighting fixtures. The ideal flip height is a calculation that prevents the plant from rapidly growing too tall for its environment.
Understanding the Flowering Stretch
The change in the light cycle initiates a powerful biological response known as the flowering stretch. This is a period of rapid vertical growth that occurs immediately after the light shift, driven by hormonal changes within the plant. The reduction in daylight hours alters the balance of plant growth regulators, promoting stem elongation and internodal length. This accelerated growth is the plant’s evolutionary strategy to compete for light, ensuring flower sites are exposed to maximum sunlight. The stretch typically begins within the first week of the 12/12 light cycle and peaks during the second and third weeks. Many strains double or even triple their vegetative height during this vertical surge before growth slows down and the plant focuses its energy on flower development.
Calculating Optimal Flip Height
Determining the exact height to initiate the 12/12 light cycle requires a calculation based on the constraints of the grow space. The primary goal is ensuring the plant’s final height, after the stretch, maintains a safe distance from the light source. The maximum usable height is found by subtracting the vertical space needed for the light fixture and the necessary buffer zone from the total ceiling height. The buffer zone, typically 12 to 18 inches, is the distance between the canopy top and the light, preventing light burn.
Once the maximum final plant height is established, the optimal flip height is estimated using the plant’s expected stretch factor. The formula is: (Maximum Ceiling Height – Light/Fixture Distance – Buffer Zone) / Stretch Factor = Optimal Flip Height. For example, if a grower has a 72-inch ceiling, the light fixture requires 6 inches, and a 12-inch buffer is needed, the maximum safe plant height is 54 inches. If the strain has an expected stretch factor of 2.5, dividing 54 inches by 2.5 indicates an optimal flip height of approximately 21.6 inches. This calculation turns the subjective decision of “when to flip” into a predictable, measurable process.
Strain Genetics and Timing Considerations
The most significant variable affecting the flip height calculation is the inherent genetic makeup of the strain being cultivated. Different genetic profiles, broadly categorized as Indica or Sativa, possess distinct growth patterns and stretch factors. Indica-dominant strains are genetically programmed for a more compact, bushier structure, reflecting their evolutionary origin in harsher, cooler climates. These strains typically exhibit a shorter, more moderate stretch, increasing their vegetative height by 50% to 100%, corresponding to a stretch factor of 1.5x to 2x.
Conversely, Sativa-dominant strains are characterized by a taller, slimmer profile and a much more vigorous vertical stretch. These strains commonly stretch to 2.5 times or even 3 times their height at the time of the flip. Therefore, a Sativa-dominant plant must be flipped at a significantly shorter vegetative height than an Indica-dominant plant to achieve the same final canopy height.
Managing Height Through Training Methods
Cultivators can proactively influence the decision of when to flip by employing various plant training methods during the vegetative phase. These techniques manipulate the plant’s structure, promoting lateral growth and a wider canopy instead of a single, tall stalk. This approach allows the grower to flip the plant later, or at a slightly greater height, while still managing the vertical space effectively.
Topping and FIMing
Techniques like topping and FIMing involve strategically removing the growth tip. This temporarily halts vertical growth and forces the plant to distribute growth hormones to multiple side branches. This results in a plant with multiple main colas and a more even canopy, which reduces the overall vertical stretch focused on a single stem.
Low Stress Training (LST) and SCROG
Low Stress Training (LST) involves gently bending and securing branches downward to encourage lower growth sites to develop, creating a flat, wide profile. The Screen of Green (SCROG) method further utilizes LST by weaving branches through a horizontal net, forcing all developing flower sites to grow at a uniform height beneath the light. Training methods like these redistribute the plant’s energy, maximizing light exposure and ensuring efficient use of the vertical space available.