06/20/2026
One of the reasons I like to wrap up most of our growing before it really gets hot….🥵
Thanks Farmer Bev for always educating! Texas Tested Seeds
You spend months tending to your tomato plants, watching them shift from tiny yellow blossoms to heavy, beautiful globes. You pick the perfect fruit, bring it into the kitchen, slice through the middle, and... instead of a juicy interior, you are greeted by a tough, pale, woody core.
This is known as “internal whitening” (or white core disorder). It is actually a common physiological response to environmental stress.
Internal whitening is a physiological disorder, meaning it is not caused by a fungus, bacteria, or virus. It won’t spread from plant to plant like late blight. Instead, it occurs when the internal tissue walls of the tomato fail to ripen properly, turning into a hard, white, or greenish corky substance.
Often, a tomato afflicted with internal whitening looks completely flawless on the outside. The mystery only unravels when you cut it open.
What causes a tomato to essentially build a wall of cardboard inside itself? It usually comes down to a perfect storm of weather and soil chemistry.
Tomatoes get their signature red color from an antioxidant called lycopene. However, the chemical process that creates lycopene is highly sensitive to temperature.
When consistent daytime temperatures climb above 85°F, the plant's ability to produce lycopene slows down or stops entirely. The outside of the tomato might still look red due to other pigments, but the heat-stressed interior remains pale, hard, and underdeveloped.
Also, Potassium (K) is the driver behind fruit ripening and sugar distribution. Even if your soil has plenty of potassium, the plant might struggle to absorb it. High soil temperatures (often made worse by black landscape fabric), compacted soil, or heavy fruit loads can prevent the roots from drawing up enough potassium. When plant tissue levels of potassium drop, internal whitening or "yellow shoulder" disorder often follows.
Some older varieties with large, distinct seed cavities (locules) are simply more susceptible to internal whitening. Modern "beefsteak" types and cherry tomatoes tend to handle these stresses a bit better.
So, is it safe to eat? Yes, tomatoes with internal whitening are completely safe to eat.
Because it is a environmental ripening issue and not a rot, there are no toxins or pathogens involved. However, the white parts are tough, fibrous, and largely tasteless. The best practice is simply to take a sharp knife, cut out the woody white core, and enjoy the rest of the juicy sections.
While you can't control the summer weather forecast, you can take a few steps to protect your crop from the stresses that cause white cores.
First, an inch or two of straw, mulch, or shredded leaves keeps the soil cool and moist, allowing roots to smoothly absorb potassium.
Second, throwing a light shade cloth like 30% over your tomato canopy during extreme heatwaves drops the temperature just enough to keep lycopene production active.
Finally, look for modern hybrids or varieties explicitly noted for heat tolerance if you live in a region with scorching summers (aka Texas).
