Tomato cracking is a physiological fruit disorder, not a diagnosis that can be read from greenhouse humidity alone. A useful interpretation connects the crack pattern with fruit growth, skin elasticity, water movement, cultivar, fruit load, and temperature. Humidity can change the balance around ripening fruit, but it is one condition in a multi-factor process.
Recognize the crack pattern
UConn Extension describes radial cracks as lengthwise splits from the stem end, concentric cracks as rings around the shoulder, and irregular cracks as random shoulder splits. Rain checking appears as many small superficial cracks, while russeting is a fine brown cracking of the cuticle. These are growth injuries; deep openings can later allow fungi or bacteria to enter, which is a secondary consequence rather than the original cause. (UConn Extension)
The pattern helps frame the question, but it does not identify a single trigger. Look at the fruit stage and tissue around the shoulder alongside the recent greenhouse conditions.
Why protected crops can still crack
Purdue’s protected-cropping discussion explains that cracking can occur in high tunnels and greenhouses even when soil moisture is more consistent than in a field. Under high RH with moist soil, water is less likely to move back from fruit toward leaves through transpiration. If fruit water pressure rises while the skin cannot expand at the same pace, cracking becomes more likely. Heat can also raise internal fruit pressure and weaken skin strength. (Purdue Vegetable Crops Hotline)
This is a relationship between water supply, movement between fruit and leaves, fruit temperature, and skin properties. It should not be simplified into “high RH causes cracks,” or into a promise that changing room air will prevent them.
Cultivar and fruit load change the comparison
The University of Delaware discusses cracking in field tomatoes; that setting provides a comparison for protected crops. It links cracking susceptibility to skin elasticity, thin skin tissues, fruit size, temperature and humidity variability, and fruit load. Large-fruited varieties are often vulnerable, but many cherry tomatoes can crack too; small fruit is not automatically protected. The publication also identifies low fruit load and elevated fruit temperature as factors to consider. (University of Delaware Cooperative Extension)
Interpret the greenhouse record
Compare crack type, cultivar, fruit load, ripeness, canopy cover, root-zone moisture, air humidity, and temperature history. The record is for separating interacting causes, not for assigning a universal set point. Root-zone moisture vs. air humidity explains why the two measurements answer different questions. For persistent cracking or suspected secondary infection, consult a qualified crop advisor.
Related project questions
Keep fruit symptoms separate from other crop responses. See edema and the water-balance question and tomato pollination conditions. For the wider project context, return to agricultural humidity control.
