Defoliation is a horticultural practice involving the selective removal of fan leaves to manage canopy density. The flowering stage marks the plant’s transition from vegetative to reproductive growth, triggered by a change in the light cycle. Whether to perform defoliation during the first week of this transition is debated among growers. Understanding the plant’s physiological state is necessary before introducing this high-stress intervention.
Plant Physiology During Early Flowering
The first week of flowering is characterized by the “stretch,” a rapid growth phase where the plant significantly increases its vertical height and internodal spacing. This biological response to the change in photoperiod signals the plant to grow taller to compete for light before dedicating resources to flower production.
This vertical growth is primarily driven by increased production of specific plant hormones. Gibberellins promote cell elongation within the stems, while changes in auxins influence the shift from lateral branching to vertical expansion.
During this initial week, the plant operates at peak metabolic demand, mobilizing massive amounts of stored carbohydrates and nutrients. It rapidly builds the stems and branches that will support the final size and weight of the developing flowers. This high-demand state means the plant is already undergoing a natural, programmed form of stress as it establishes future bud sites.
Rationale for Defoliating in Week 1
The primary argument for defoliating in the first week centers on maximizing light penetration to the lower and middle portions of the plant. Large upper fan leaves often shade nascent bud sites beneath them. Removing these leaves allows light to reach deeper into the canopy, encouraging lower sites to develop into full-sized flowers instead of small “popcorn” buds.
Another benefit is the immediate improvement of air circulation within the dense foliage. A thick, humid canopy is conducive to fungal pathogens like mold and mildew. Selectively removing overlapping leaves substantially reduces the risk of these issues.
Strategic leaf removal also redirects energy. The plant expends energy maintaining every leaf, even those deeply shaded and inefficient. Removing these non-productive fan leaves forces the plant to divert that maintenance energy into the developing flowers.
The technique, often part of a process called “lollipopping,” involves stripping the lower third of the plant to focus all resources on the top canopy. When performing this initial defoliation, the cultivator should aim to remove approximately 20 to 30% of the total foliage, focusing on the largest fan leaves that are blocking light from the future main colas.
Potential Negative Impacts of Early Defoliation
Applying a high-stress technique like defoliation during the first week of flowering poses several risks. The most immediate risk is stunting the vigorous vertical growth of the stretch phase. If the plant dedicates energy to repairing wounds instead of elongating stems, the final height and overall size will be reduced, potentially translating to a lower yield.
Defoliation can induce significant shock, temporarily halting growth for several days as the plant recovers. This interruption disrupts the hormonal balance driving rapid expansion, causing the plant to fall behind its optimal growth schedule. Metabolic resources may be diverted away from reproductive goals toward immediate survival and repair.
The removal of fan leaves also eliminates stored nutrient reservoirs. Large fan leaves contain mobile nutrients, such as nitrogen and phosphorus, which the plant reallocates to developing flowers later in the cycle. Prematurely removing too many leaves can cause nutrient deficiencies to appear earlier in the flowering stage.
If the stress is too severe, the plant’s production of defense hormones, like jasmonates, may increase. This redirection of chemical signaling resources toward defense mechanisms can come at the expense of flower development and resin production.