Apical Dominance
The tendency of a plant's main growing tip to suppress the growth of lower side branches through hormonal signaling.
Apical dominance is real, well-studied plant biology — not grower folklore. It's why cannabis plants left alone tend to grow one tall central cola with weaker side branches. The whole practice of topping, FIMing, and low-stress training exists to defeat it. What's less settled is the exact hormonal mechanism; the classic 'auxin from the tip suppresses side buds' story has been complicated by newer research on strigolactones and sugar signaling.
Definition
Apical dominance is the phenomenon in which the main shoot tip (the apical meristem) of a plant inhibits the outgrowth of axillary buds lower down the stem. The result is a plant that grows tall and central rather than bushy. It occurs across most vascular plants but is particularly pronounced in cannabis, which naturally forms a dominant central cola when grown untrained. Strong evidence
How it works
The classical explanation is that auxin (indole-3-acetic acid) produced at the shoot tip travels downward and suppresses lateral bud growth [1][2]. Modern research has revised this picture: strigolactones act as direct inhibitors of bud outgrowth, cytokinins promote it, and sugar availability to axillary buds appears to be a major trigger for their release from dormancy [3][4]. In practice, when the apex is removed or damaged, the hormonal and sugar-flow balance shifts, and dormant side branches begin to elongate within days. Strong evidence
What it means for cannabis growers
Left alone, a cannabis plant will typically produce one large top cola and progressively smaller buds down the stem. Growers who want a flatter, more even canopy — and more equally sized colas — deliberately disrupt apical dominance. Common techniques include topping (cutting the main shoot tip), FIMing (partial removal), low-stress training (bending the main stem horizontal), and mainlining. Auto-flowering cultivars are generally topped less aggressively because they have a fixed lifecycle and less time to recover. Strong evidence
What it doesn't do
Apical dominance does not directly control potency, cannabinoid ratios, or terpene profile. Claims that topping 'increases THC' are folklore — training changes yield distribution and canopy structure, not the plant's chemotype Anecdote. Total yield gains from breaking apical dominance are real but modest and depend heavily on light, space, and vegetative time.
Sources
- Peer-reviewed Cline, M. G. (1997). Concepts and terminology of apical dominance. American Journal of Botany, 84(9), 1064-1069.
- Peer-reviewed Leyser, O. (2009). The control of shoot branching: an example of plant information processing. Plant, Cell & Environment, 32(6), 694-703.
- Peer-reviewed Gomez-Roldan, V., et al. (2008). Strigolactone inhibition of shoot branching. Nature, 455(7210), 189-194.
- Peer-reviewed Mason, M. G., Ross, J. J., Babst, B. A., Wienclaw, B. N., & Beveridge, C. A. (2014). Sugar demand, not auxin, is the initial regulator of apical dominance. PNAS, 111(16), 6092-6097.
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Related
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