Topping is a pruning technique that involves removing the main growth tip of a plant to encourage lateral branching, maximizing the plant’s overall canopy size. This practice switches the plant from growing tall and thin with a single dominant stalk to growing wide and bushy with multiple main stalks, which increases potential yields or creates a more aesthetically pleasing shape. Because topping is a high-stress technique, the timing of the cut is the most important factor determining its success. Applying this technique at the wrong time can severely damage the plant, stunt its growth, or compromise its ability to produce flowers or fruit.
How Topping Alters Plant Growth
Plants naturally exhibit a growth pattern known as apical dominance, where the main central stem grows vigorously while suppressing the development of side branches. This dominance is regulated by the plant hormone auxin, which is produced in the main growing tip. Auxin travels downward, effectively signaling the lateral buds (nodes) to remain dormant or to grow slowly.
Removing the apical meristem through topping immediately stops the downward flow of auxin. This disruption releases the lateral buds from their suppression, allowing them to activate and begin rapid growth.
Concurrently, the concentration of another hormone, cytokinin, which promotes cell division and shoot branching, increases in the lateral nodes. This hormonal shift redirects the plant’s energy from vertical growth to horizontal or lateral development.
The result is the formation of two or more new main colas from the nodes immediately below the cut, creating a wider, bushier structure that better utilizes light exposure. This redistribution of energy prevents the formation of a single, tall stalk.
The Ideal Vegetative Timing Window
Topping must be performed exclusively during the vegetative growth phase. The plant needs to be robust and healthy enough to handle the immediate shock of the procedure and have sufficient time to recover.
For the first topping, wait until the plant has developed at least three to five distinct sets of true leaves, known as nodes. Cutting should occur just above the third or fourth node from the bottom of the plant.
This stage ensures the plant has an established root system and enough leaf surface area to generate the energy required for rapid healing and new shoot development. Topping too early, especially during the seedling stage, is highly risky because the young plant lacks the necessary reserves and may become severely stunted.
When Topping Becomes Detrimental
The window for successful topping closes the moment the plant transitions from the vegetative phase to the reproductive (flowering/fruiting) phase. This transition is signaled by hormonal changes that prepare the plant for flower or fruit production.
If a plant is topped after the onset of flowering, the procedure becomes detrimental because the plant is forced to spend valuable reproductive energy on healing the wound. This recovery period significantly delays the development of flowers or fruit, directly reducing the overall yield.
Late topping can also cause severe stress, which may lead to adverse outcomes like the development of abnormal reproductive structures in some plant species. Once a plant has entered the flowering stage, its hormonal balance shifts to prioritize floral growth, and it cannot easily revert to a vegetative recovery state.
Therefore, the window for topping is closed once the first reproductive structures, such as small buds or flower precursors, have begun to form.
Growth Management Techniques If The Window Is Missed
If the optimal topping window is missed, growers should avoid high-stress cuts and use alternative, less intrusive training methods. Low-Stress Training (LST) is an excellent technique that involves gently bending and tying down the main stem and branches to create a wider, more level canopy without cutting.
Another option is FIMing, a variation of topping where only about 75% of the new growth tip is removed. This technique is less stressful than a complete top and can still encourage multiple new colas.
Strategic defoliation, the removal of select large fan leaves, can also be employed to improve light penetration to lower bud sites and increase airflow. These methods manage the plant’s shape and light exposure without forcing the severe hormonal disruption and recovery time associated with late topping.