Tomato cracking, the splitting of the fruit’s skin, is a common physiological disorder that frustrates gardeners and commercial growers alike. This damage occurs when the tomato’s internal growth rapidly exceeds the limited elasticity of its outer layer. Cracking results from rapid environmental changes, particularly those that affect the plant’s water uptake.
The Internal Pressure Mechanism
The cause of tomato cracking is an imbalance between the water pressure inside the fruit and the mechanical strength of the skin. Water uptake is governed by osmosis, which drives water into the fruit’s cells, increasing turgor pressure. This pressure causes the fruit flesh to swell.
The skin, or epidermis, of the tomato fruit is composed of an outer waxy layer called the cuticle, which provides a protective barrier. As the fruit grows, this cuticle and the underlying epidermal cells must stretch to accommodate the expanding pulp. The skin has a finite elasticity, and when the internal pressure builds too quickly, the skin cannot expand at the same rate.
Cracking is most likely to occur as the tomato begins to ripen and change color. During this phase, cell wall modifying proteins disassemble the cell wall structure, causing the fruit to soften. This softening transfers the internal pressure directly to the epidermis and the cuticle, which are less flexible than the internal tissues.
The inability of the skin to deform further leads to mechanical failure, especially on fruit nearing maturity. The skin tears at its weakest point when the turgor pressure generated by the rapid influx of water overcomes the tensile strength of the cuticle and epidermis.
Managing Environmental Triggers
Preventing cracks requires managing the external conditions that initiate the pressure imbalance. The most important practice is maintaining a consistent supply of soil moisture throughout the growing season. Periods of drought followed by heavy rain or excessive watering are the primary triggers for the rapid water uptake that causes splitting.
Tomato plants generally require one to two inches of water per week, delivered slowly and deeply to the root zone. Drip irrigation or soaker hoses are effective because they apply water directly to the soil, avoiding the rapid, surface-level absorption that often happens after heavy rainfall. Watering deeply also encourages the plant to develop deep, resilient root systems.
Applying a two- to three-inch layer of organic mulch, such as straw or shredded leaves, helps stabilize soil moisture. Mulch reduces water evaporation and insulates the soil to keep root temperatures consistent. This buffers the plant against sudden changes in water availability, whether from a dry spell or a downpour.
Gardeners can also select varieties that are genetically less susceptible to splitting. Modern hybrids and smaller-fruited varieties have been bred to possess a tougher skin or a higher tolerance for fluctuating water levels. High-nitrogen fertilizers promote overly succulent, fast growth that increases the risk of cracking, so using balanced nutrition is another management technique.
Radial vs. Concentric Cracks and Harvest
Tomato cracks are categorized into two main types based on their appearance and the conditions that typically cause them. Recognizing these patterns can help the gardener adjust their management practices.
Radial cracks appear as splits that radiate outward from the stem end, like spokes on a wheel. These are the most severe type of cracking, caused by a single, sudden, and severe influx of water, such as heavy rain after an extended dry period.
Concentric cracks form circular rings around the stem end of the fruit. These cracks are associated with slower, prolonged environmental stresses, such as high temperatures or significant differences between day and night temperatures. They can also occur when ripe fruit is left on the vine for too long.
A cracked tomato is still edible and safe to consume if it is harvested immediately after the damage occurs. However, the open wound makes the fruit vulnerable to decay, pests, and pathogens. To salvage the fruit, it must be picked immediately, and any damaged sections should be cut away before consumption.