Why Aren't My Tomatoes Turning Red? 7 Possible Reasons

Anticipation is likely one of the reasons it seems to take forever for your tomatoes to turn red. Dozens of varieties exist and tomatoes are fairly easy to grow, but it's the fresh, juicy taste and texture that make tomatoes the most popular crop grown in home gardens across the United States.

Waiting for them to ripen to perfect red can seem endless, but besides anticipation there are several non emotion-based reasons for why your tomatoes are still green. Here are some of the most common reasons why your tomatoes aren't turning red, plus what you can do to speed up the ripening process.

Temperature Too Hot or Too Cold

Temperature is one of the bigger factors for ripening tomatoes and a few degrees too hot or too cold puts the process on hold or even stops ripening altogether. The ideal temperature tomatoes need to acquire their red color is 68 to 77 degrees F. At 85 degrees, the production of lycopene ceases leaving large green fruits on the vine until temperatures lower to more better levels. Temperatures consistently below 60 degrees F. also inhibit ripening.

Fruits that are fully mature and have a slight blush can be harvested and brought indoors to finish ripening. They do not need to sit in a sunny window as long as the correct temperature is provided.

Too Much Direct Sunlight

Even though it might seem counterintuitive, too much sun exposure can slow down ripening. The heat is more important than light for ripening, and too much bright, hot, direct sunlight can raise temperatures to levels that inhibit lycopene production. Pruning leaves away from mature tomatoes to give them more sun exposure can also cause sunscald and cracking.

Too Much Water

Tomato plants need 1 to 2 inches of water per week when vines are actively growing and producing fruit. But once fruits reach their mature size, ripening occurs more quickly if irrigation is reduced or even stopped completely. Less water stresses the tomato plant and sends it into survival mode. The plant will focus energy into producing viable seed, which helps accelerate ripening.

Insufficient Nutrients

Tomatoes require a lot of nutrients and micronutrients throughout the growing season. Phosphorous and potassium are particularly important for the production and synthesis of lycopene in the fruits. Insufficient amounts can cause slow or uneven ripening. When the first small fruits appear on the plant, feed with a fertilizer higher in phosphorous such as and NPK 5-10-5.

Too Much Nitrogen

Tomato plants benefit from an application of balanced fertilizer such as an NPK 10-10-10 early in the season. This supports vine and foliage growth and encourages good root development and flower production. Once mature fruits are on the vine, fertilizing with a product that contains too much nitrogen can take away from ripening by refocusing energy on foliage growth.

Once green fruits have reached a fully mature size, withhold fertilizer and allow the natural processes of ripening to take place in the fruit.

Lack of Pruning

Limiting the number of vines on a plant by removing early suckers is another way to focus energy into the production and ripening of fruit. Not every vine produces fruit and plants with unproductive vines or vines overloaded with fruit will struggle. This is especially true for determinate type tomato plants that produce many fruits all at the same time. Early pruning of your tomato plants results in higher quality fruit that ripens more easily and quickly.

It's Not Supposed to Be Red

It's important to understand, starting out, what your tomato type will look like when fully ripe. Many varieties ripen to different shades of red or may be orange, pink, purple and even striped. If you're waiting for your tomato to turn red, make sure that's the color it's supposed to be when it's ready to pick.

Check your seed package for how many days to harvest for the tomato variety you've chosen. Some varieties need more or less growing time and may not work as well in your climate.