Pruning is the selective removal of parts of a tomato plant. This common practice influences the final harvest, but whether it increases yield depends on how a gardener defines “yield.” Understanding plant physiology and variety is necessary to decide if and how to prune.
The Relationship Between Pruning and Yield
Pruning directly influences a tomato plant’s resource allocation, determining the size and quality of the fruit. The practice diverts the plant’s energy, specifically carbohydrates produced through photosynthesis, away from new vegetative growth and toward the existing fruit. These carbohydrates allow the fruit to swell and ripen.
Removing new stems, known as suckers, reduces the number of growing points competing for energy. This action typically results in fewer total fruits set on the plant. However, the remaining tomatoes receive a concentrated supply of resources. Consequently, the result is often a harvest of larger, higher-quality tomatoes, which can increase the usable yield by weight or value, even if the total fruit count is lower.
Pruning also contributes to yield indirectly by improving the plant’s overall health. Removing excess foliage increases air circulation around the stems and leaves, reducing humidity within the plant canopy. This drier environment is less favorable for the development and spread of common fungal diseases like early blight or powdery mildew, ultimately protecting the existing fruit.
Determining When and How to Prune
The decision to prune a tomato plant is dependent on its growth habit, which falls into two categories: determinate and indeterminate. Determinate varieties, often called “bush” tomatoes, grow to a predetermined height and set their fruit within a short period. These types require minimal pruning, as removing too much foliage or too many suckers can significantly reduce the overall crop.
Indeterminate varieties are vine-like and continue to grow, flower, and set fruit until the first frost. These plants benefit the most from pruning, as their continuous growth can become unwieldy and dense without intervention. The primary technique involves removing suckers, which are small shoots that emerge in the “V” shape between the main stem and a leaf branch.
If left to grow, a sucker will develop into a full, fruit-bearing stem that competes with the main vine for resources. Gardeners typically “pinch” off these small shoots with their fingers when they are less than four inches long to direct the plant’s energy into the main stem. This focused pruning helps manage the plant’s size, improves light penetration, and ensures the development of larger fruit on the remaining stems.
It is important to stop pruning later in the season, typically one to two weeks before the expected final harvest or when the plant reaches its desired height. Removing the growing tip of the main stem, called “topping,” shifts the plant’s remaining energy toward ripening the fruit that has already set. This action helps ensure the last tomatoes mature before the season ends.
Risks and Trade-offs
Pruning, while beneficial for fruit quality and plant health, carries specific risks if performed incorrectly or excessively. One common negative outcome is sunscald, which occurs when too much protective foliage is removed. This exposes the developing fruit to intense, direct sunlight, causing pale, blotchy, or blistered areas on the skin.
The foliage naturally provides a canopy of shade, and excessive cutting eliminates this protection, making the fruit vulnerable, especially in hot climates. Larger tomato varieties are often more susceptible to sunscald because they take longer to grow. Care must be taken to leave enough leaves on the upper parts of the plant to shade the ripening fruit.
Another trade-off involves the risk of disease introduction. Every cut creates a wound that can serve as an entry point for bacterial or fungal pathogens. If pruning tools are not cleaned between plants, diseases can spread from an infected plant to a healthy one. To mitigate this risk, tools should be disinfected with rubbing alcohol or a bleach solution before starting and when moving to a new plant.