Plants naturally favor vertical growth, a tendency that often results in tall, spindly specimens rather than the dense, bushy shape many gardeners desire. Shifting a plant’s energy from upward elongation to lateral expansion is possible through several targeted techniques. Controlling the growth habit is valuable for aesthetics, improving yield in edible plants, and enhancing a plant’s overall health by allowing better light and air circulation into the canopy. Successfully forcing plants to grow outward requires understanding the biological mechanisms driving their vertical reach and applying specific mechanical and environmental controls to override them.
Understanding Apical Dominance
The reason plants grow primarily upward is rooted in a biological process called apical dominance. This phenomenon is controlled by the plant’s main growing tip, or apical meristem, which is located at the apex of the stem. The meristem produces a powerful plant hormone called auxin, which is transported downward. Auxin actively suppresses the development of lateral buds located further down the stem. This inhibition ensures that the plant prioritizes height, allowing it to compete for sunlight by growing above neighboring vegetation. Removing the apical meristem is the immediate and most effective way to break this dominance and promote side growth. Once the downward flow of the inhibitory auxin signal is interrupted, the dormant lateral buds are released from suppression and begin to grow outward, initiating the desired bushy structure.
The Primary Technique: Pinching and Topping
The most direct way to encourage lateral growth is by physically removing the apical meristem through pinching or topping. Pinching involves the removal of soft, new growth, typically done using just the thumb and forefinger on tender, non-woody stems. Topping, or heading back, is a similar but more severe technique, usually involving clean, sharp shears to cut back a tougher stem to a specific node or set of leaves. The cut should be made just above a node, which is the point where a leaf and a dormant lateral bud are attached to the main stem. The removal of the terminal bud forces the plant to send growth hormones and energy to the lateral buds immediately below the cut, leading to the formation of multiple new branches.
Manipulating Light and Nutrients
Environmental factors can be adjusted to influence a plant’s growth habit without requiring physical pruning. Insufficient light intensity or poor light distribution causes etiolation, where the plant grows long, weak stems with widely spaced leaves as it stretches to find a light source. Providing intense, uniform light helps to naturally suppress stem elongation and encourages the plant to develop a more compact, dense form. The color spectrum of the light also plays a role, with a high blue-to-red light ratio tending to result in shorter, bushier plants compared to a high red-to-blue ratio. Regular rotation of the plant prevents one side from receiving more light than the other, ensuring that growth is balanced and the plant develops evenly.
Nutrient Balance
Fertilizer composition is another powerful tool, specifically the balance of Nitrogen (N), Phosphorus (P), and Potassium (K), represented by the N-P-K ratio. Nitrogen primarily fuels vegetative growth, promoting leafy development and stem elongation. Using a fertilizer with a high nitrogen number (e.g., 20-5-5) will encourage vertical growth, which is the opposite of the desired bushy structure. To promote structural and lateral growth, use a fertilizer that is more balanced or has a lower relative amount of nitrogen, such as a 10-10-10 or 5-10-10 ratio. This nutrient balance supports the development of strong stems and roots rather than excessive foliage, which is important when encouraging a plant to branch out and form a robust frame.
Structural Training Methods
Beyond pruning and environmental controls, physical manipulation can be used to redirect growth, especially for species with woody stems or for vines. Low-Stress Training (LST) is a technique that involves gently bending the main stem or branches and securing them into a horizontal position using soft ties or gardening wire. This forces the plant’s vertical energy into the side branches, which then begin to grow upward toward the light, effectively creating multiple main shoots and a wider canopy. By keeping the main stem bent and tied down, the plant is encouraged to maintain a flat, even canopy structure rather than a single vertical column. This technique minimizes stress compared to cutting and increases light exposure to lower parts of the plant, promoting uniform growth.