Tomato cracking, also known as fruit splitting, is a widespread physiological disorder that is not caused by disease or pests. It occurs when the tomato skin cannot accommodate the rapid expansion of the fruit’s interior volume. Splitting manifests in two patterns: radial cracks, which appear as vertical lines radiating outward from the stem end, and concentric cracks, which form circular rings around the stem scar. Radial cracking is the more serious type because the deep split exposes the flesh, creating an entry point for fungi and bacteria and leading to rapid rot.
Primary Mechanism: Inconsistent Water Uptake
The fundamental cause of tomato cracking is a sudden change in the availability of water to the plant roots. As a tomato ripens, its outer skin naturally loses flexibility and the ability to stretch. If the plant experiences a dry period, the skin may toughen further, making it less elastic.
When drought or low soil moisture is abruptly followed by heavy rain or excessive irrigation, the roots rapidly absorb the influx of water. This water is quickly transported into the fruit’s cells, causing them to swell instantaneously. The resulting internal pressure builds up faster than the inflexible skin can stretch, leading to rupture.
The speed of this water uptake and subsequent expansion is the factor, not the total volume of water. This rapid internal growth forces the fruit to burst its outer layer. Damage is most likely to occur as the fruit approaches maturity, particularly when it begins to change color, as the skin’s strength is naturally reduced.
Environmental Factors That Increase Risk
Temperature and Humidity
Environmental conditions beyond watering errors significantly increase a tomato’s susceptibility to cracking. High temperatures combined with high humidity exacerbate the problem by stressing the plant and affecting skin development. This combination encourages rapid, uncontrolled swelling during the fruit-ripening stage. High humidity also allows the plant to absorb moisture directly through its leaves, bypassing the controlled root system.
Genetic Susceptibility
The tomato variety itself plays a large role, as susceptibility is partly genetic. Cultivars with naturally thin skins or large fruit size, such as many heirloom or beefsteak types, are inherently more prone to splitting. Conversely, thick-skinned hybrid varieties are often bred with greater tensile strength, offering better resistance to rapid pressure changes.
Excessive Fertilization
Aggressive fertilization, particularly the excessive application of nitrogen, also increases the risk. High nitrogen levels promote quick vegetative growth and rapid fruit expansion. This causes the fruit’s interior to grow too quickly for the skin to keep pace, leading to cracking even if water levels are consistent.
Strategies for Preventing Tomato Cracking
The most effective method for preventing fruit splitting is to maintain the most consistent soil moisture level possible throughout the growing season. This means avoiding the cycle of allowing the soil to dry out completely and then soaking it with a heavy application of water. Deep, less frequent watering is generally preferable to shallow, daily watering, as it encourages deeper root growth and stabilizes the moisture level.
Applying a thick layer of organic mulch, such as straw or wood chips, around the base of the plants is a highly effective technique. Mulch helps to regulate soil temperature and significantly reduces water evaporation, which prevents the rapid drying and subsequent soaking that causes pressure spikes. This insulating layer helps to buffer the plant against sudden environmental shifts.
Another management strategy is to adjust the timing of the harvest. Picking tomatoes once they begin to show the first blush of color, often called the “breaker stage,” removes the fruit from the vine before it is fully exposed to the highest risk period for splitting. The fruit can then finish ripening indoors without being subject to unpredictable rain events.
For future seasons, selecting crack-resistant varieties is a proactive measure. Look for cultivars specifically labeled as split-resistant or those known for having tougher skins, such as certain paste or determinate varieties. These varieties possess the genetic traits necessary to better withstand the internal pressure changes that lead to splitting.