Causes of Uneven Tomato Coloring

Most people choose tomatoes that are ripe, clean, and evenly colored, usually a rich red or another uniform shade, depending on the variety. They should look fresh and delicious.

Because of this, tomato growers face strong competition. Even small imperfections can affect the value of their crop. One common problem is uneven coloring. When tomatoes don’t turn fully red and have green or yellow patches, these tomatoes are harder to sell, lower in grade, and cost more to sort. This leads to lower profits and unhappy customers.

In this post, we’ll explain the common causes of uneven tomato ripening and share simple tips to help grow better, more uniform tomatoes.

Common Ripening Issues and What They Mean

Tomato ripening problems can be frustrating, especially when your fruits look patchy or uneven. Many of these issues stem from environmental stress, nutrient imbalances, or disruptions in the plant’s hormone regulation, particularly ethylene, the natural hormone responsible for ripening. Here are two common ripening disorders and what they typically indicate:

Blotchy ripening (Greenback)

This condition appears as irregular, discolored patches, often green, yellow, or gray, that don’t turn red, regardless of how long the fruit is left to ripen. These blotches can show up anywhere on the tomato’s surface.

The main culprits include high temperatures, significant day-to-night temperature swings, and cool nights during the ripening period. Nutrient imbalances also play a part, particularly low potassium levels or excess nitrogen, which promotes leafy growth at the expense of fruit development. Viral disease and heavy whitefly infestation can also cause blotchy ripening.

Yellow shoulder

Perhaps the most recognizable ripening issue, Yellow Shoulder occurs when the top of the tomato, near the stem, stays yellow or green while the rest of the fruit ripens normally.

This condition is primarily driven by heat stress, especially during prolonged periods of temperatures above 85–90°F (30–32°C). High temperatures interfere with the production of lycopene, the red pigment, particularly in the fruit's shoulder area. Direct sun exposure can worsen the problem by "sunburning" the top of the fruit. Additionally, insufficient potassium, essential for moving sugars and activating enzymes needed for ripening, can contribute significantly to this disorder.

Main Causes for Uneven Tomato Coloring

When tomatoes don’t ripen evenly, it can be confusing and disappointing. This usually happens because of three main things: stress from the environment, problems with nutrients, or the natural traits of the tomato variety.

Extreme temperature 

One of the biggest problems is temperature. When it gets too hot, above 90°F(32°C), the tomato’s natural red color doesn’t develop properly. The top part of the tomato, which gets the most sun, often stays green or yellow while the rest turns red. On the other hand, when it gets too cold, below 60°F(15°C), the red pigment also doesn’t form correctly, and the fruit can look pale or patchy.

Light intensity and duration

Light also plays an important role. Tomatoes need the right amount of light to ripen well. Too much direct sunlight can damage the tomato’s surface and stop the red color from forming, especially at the top. But if the tomato plant is too leafy and the fruit is hidden in shade, the tomatoes don’t get enough light either. This leads to pale or uneven coloring.

That’s why some commercial farmers use LED inter-canopy lights placed between the plants to make sure the whole plant gets even lighting. This helps the tomatoes grow and ripen more evenly.

Water stress

If a tomato plant gets too much water or too little at different times, it can become stressed. This stress affects how well the plant sends nutrients to the fruit. When parts of the plant are stressed, those fruits may ripen more slowly or unevenly, with some parts staying green longer than others.

Nutrient imbalances

Tomatoes need the right balance of nutrients to ripen properly. Potassium helps the tomato develop its color, move sugars, and keep cells working well. If there’s not enough potassium (K) in the soil, tomatoes can end up with uneven ripening, often showing blotchy patches or even white areas inside the fruit. Too much nitrogen (N) is also a problem. While nitrogen helps plants grow, too much of it causes the plant to grow lots of leaves instead of focusing on the fruit. This can delay ripening and create a thick canopy that blocks light from reaching the tomatoes.

Genetic and varietal factors

Lastly, the type of tomato you grow matters. Some varieties naturally ripen more evenly than others. For example, the Early Girl tomato is known for ripening quickly and evenly. It turns from green to red in a smooth, steady way. On the other hand, the Green Zebra tomato is meant to look different. It keeps much of its green color even when fully ripe, with yellow stripes. This isn’t a problem. It's just how that variety is supposed to look, due to its natural genetics.

Prevention and Management of Uneven Tomato Coloring

Now that the causes of uneven tomato coloring are better understood, several practical steps can be taken to prevent blotchy ripening and promote uniform fruit development.

Start with clean seed

Using certified, disease-free seed is essential to minimize the risk of Tomato Fruit Blotch Virus. This is the foundation of healthy crop production and one of the most important preventive measures.

Optimize growing conditions

Creating an optimal growing environment is also essential.

Lycopene, the pigment responsible for the red color in tomatoes, forms best at temperatures between 68 to 77°F (20 - 25°C). In greenhouse settings, it is helpful to use shade cloths during periods of intense heat, especially when temperatures exceed 85°F (30°C), to prevent conditions like yellow shoulder.

In winter, while increasing the temperature is a common practice, it is equally important to maintain good ventilation and consider the use of evaporative cooling systems. These measures help maintain a stable temperature and reduce humidity, both of which support even fruit coloring.

Manage lighting carefully

Tomatoes require different light intensities throughout their growth stages, so using LED grow lights with adjustable intensity is highly beneficial. Internal lighting can also help illuminate the lower parts of the plant, ensuring that all fruit receives adequate light and reducing the chance of uneven ripening due to inconsistent light exposure.

Provide balanced nutrition

Balanced nutrition is key to achieving uniform tomato color. Regular soil and tissue testing allows for accurate monitoring of nutrient levels. Fertigation programs should be carefully managed to provide enough potassium while avoiding excessive nitrogen, particularly during the fruit development and ripening stages.