The Screen of Green (SCROG) method is a plant training technique designed to maximize horizontal canopy space in a grow area, which directly enhances the efficiency of light distribution. This method uses a net or screen to encourage lateral growth, turning a single tall plant into a flat, wide plane of uniform bud sites. For the SCROG technique to succeed and deliver maximum yield, the timing of each step is crucial. Precise timing dictates how effectively the canopy fills the screen and how uniformly the plant converts light energy into flower mass.
Preparing the Plant for SCROG
The true beginning of the SCROG method is the preparatory training of the plant’s structure during the vegetative phase, not the screen installation. A sufficient vegetative growth period, often longer than in other cultivation styles, is necessary to develop a robust root system and strong primary branches. This foundational work ensures the plant has the structural integrity and energy reserves required to fill the screen effectively.
Early training techniques are necessary to break the plant’s natural apical dominance, the tendency to grow one main central stem. Topping or FIMing should be performed when the plant has developed between three and five nodes, typically occurring a few weeks into the vegetative stage. Topping involves removing the main growing tip to divert growth hormones into the side branches, creating multiple main colas.
This initial structural training must be completed early enough to allow the plant at least one to two weeks of recovery time before the screen is installed. The goal is to have a plant with multiple primary branches that are flexible and ready to be spread out horizontally. This preparation ensures the plant has the necessary architecture to immediately begin the lateral training process.
Installing the Screen and Initial Tucking
The moment to physically install the screen and begin active training is determined by the plant’s height relative to the net. The screen should be firmly fixed in place, typically between 8 and 12 inches (20-30 cm) above the growing medium. This height range allows sufficient space beneath the net for air circulation and for removing lower growth later, while keeping the canopy close to the light source.
The active SCROG process begins when the tallest shoots have grown to about 50 to 60% of the screen’s height, or just start to penetrate the net. Waiting for the plant to grow slightly through the net, about 2 inches (5 cm), signals the perfect time to start the initial “tucking.” The branches are gently bent and tucked back under the screen, forcing them to grow horizontally into an empty square.
This horizontal redirection stimulates the side branches to develop into main colas, creating a flat plane of growth. During this period, the grower must check the plants daily or every other day to tuck any new vertical growth back under the screen. This continuous, low-stress training allows the plant to stretch and fill the screen space, maximizing the number of potential bud sites that receive direct light.
Timing the Flip to Flowering
The second major timing decision in SCROG is when to transition the plant from the vegetative light cycle to the flowering light cycle (12 hours of light and 12 hours of darkness). This decision must be made before the screen is completely full because of the “flowering stretch.” Once the light cycle is changed, the plant will undergo a rapid vertical growth spurt, often doubling or even tripling its height over the first few weeks of flowering.
To account for this intense stretch, growers should initiate flowering when the screen is filled to approximately 50% to 75% capacity. Flipping at 50% is safer for highly stretchy strains, while 75% is acceptable for less vigorous or Indica-dominant varieties. The remaining empty space will be filled naturally by the stretching branches during the first two to three weeks of the flowering phase, resulting in a perfectly dense, uniform canopy.
Flipping too early leaves too much empty screen space, which reduces the potential yield. Flipping too late results in an overcrowded canopy. An overcrowded screen can cause poor light penetration to lower bud sites and restrict airflow, increasing the risk of mold or mildew. Final pruning, often called lollipopping, where all the small, unproductive growth below the screen is removed, should be performed around the time of the flip or within the first week of the flowering stretch to direct all energy toward the developing canopy.