An untrained cannabis plant grows in a natural Christmas tree shape — one dominant central stem called the apical meristem rising above all other growth, with progressively shorter lateral branches below. This structure maximizes the plant's access to sunlight outdoors, but indoors it creates a significant problem: the main cola receives excellent light while the lower branches sit in shade, producing small, underdeveloped flowers. Training is the practice of reshaping the plant to expose more of its canopy to the light source, developing multiple large colas rather than one dominant one and many small ones.
Cannabis produces a plant hormone called auxin at the growing tip of the main stem. Auxin suppresses the growth of lateral branches below it, keeping them smaller and slower-growing than the main cola. This hormonal hierarchy is called apical dominance. Every major training technique is designed to interrupt it — either by physically removing the growing tip (high stress techniques) or by repositioning the main stem so that lateral branches can rise to the same height and receive the same light (low stress techniques).
LST involves gently bending the main stem away from vertical and tying it down so that the plant grows horizontally rather than straight up. As the main stem is repositioned, the lateral branches below its canopy level begin to receive more direct light and grow vigorously upward. Over the course of one to two weeks, the previously suppressed side branches grow level with or above the original main stem, creating multiple equivalent growing tips rather than one dominant one.
The technique requires nothing more than soft plant ties (silicone tie wire or twist ties work well) and anchor points on the pot or training stakes. Begin LST when the plant has developed five to seven nodes — enough lateral branching to work with. Bend the main stem gently at a 90-degree angle and tie it down. Over the following days, continue tying new growth as it rises, spreading the canopy outward and keeping the profile as flat and even as possible.
LST is the gentlest training method and produces no open wounds, meaning the plant does not need recovery time and can be trained continuously throughout vegetative growth. It works particularly well for autoflowering plants, which cannot be topped without significant risk because their brief vegetative window leaves no time to recover from high-stress techniques.
SCROG takes the principles of LST and scales them using a horizontal net or screen placed above the plants. As the canopy grows up through the screen, branches are tucked back under and woven through the mesh, spreading growth laterally and creating an even, horizontal canopy of bud sites at a uniform distance from the light. The result is extremely efficient light utilization — virtually every bud site is at the same distance from the fixture and receives equivalent intensity.
SCROG works best with photoperiod plants because the screen-filling process requires an extended vegetative period — typically four to eight weeks of active tucking and weaving before the grower flips to flower. The general guideline is to flip when 70 to 80 percent of the screen is filled. After the flip, the plant will continue to stretch and fill remaining screen space during the first two to three weeks of flower.
Position your SCROG screen 20 to 40 centimeters above the pot tops. Too low and you will have no room to tuck and weave. Too high and the plants grow tall and lanky before reaching the screen, wasting vertical space. Many growers use adjustable screen systems that can be raised as needed.
Topping is a high-stress technique that removes the growing tip of the main stem entirely, splitting the apical meristem into two new growing tips. Within a week, both tips develop into new main colas, effectively doubling the number of dominant stems. The plant requires several days to recover, but the result is a more balanced, bushy structure with significantly more large bud sites than an untrained plant.
FIMing (named after a grower who accidentally botched a topping — "F@#k, I Missed") removes roughly 75 percent of the newest growing tip rather than the entire thing. This can produce three to five new growing tips from a single FIM, though the results are less predictable than clean topping. Both techniques are typically performed on the main stem at the fourth or fifth node and can be repeated on lateral branches as the plant develops.
Neither topping nor FIMing should be used on autoflowering plants with short vegetative windows. The recovery time costs veg days that autoflowers cannot afford. Stick to LST for autos.
Removing select leaves — particularly large fan leaves that are blocking light from bud sites — is a complementary technique to training. Strategic defoliation during late veg and the early weeks of flower opens the canopy, improves airflow, and directs the plant's energy toward bud development rather than maintaining leaves that are not contributing effectively to photosynthesis. Aggressive defoliation performed all at once stresses the plant significantly; moderate defoliation spread over multiple sessions is better tolerated.
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