Tomatoes Not Turning Red? 5 Fixes that Worked for Me

After maturity, tomatoes take 20-30 days to ripen, turning red from green. But sometimes, they never ripen at all. I know this is frustrating for home gardeners and commercial tomato farmers, so I’m going to share 5 tips I use to ensure my tomatoes are ripe on the vine.

Quick tip:

The best way to turn green tomatoes red while on the vine is to cover them with row covers or cloth when temperatures drop to about 55°F. Prune overgrown vines and feed your tomato plants 2-3 times when they’re actively growing.

Let’s dive deeper into the causes and solutions that have work for me.

What causes tomatoes not to ripen?

If your tomatoes don’t ripen as normally, many reasons are causing them not to turn red. I admit, extreme temperatures make tomato growing a challenge in most places in the United States. Most days late June through mid-September are over 90, many in the 100s.

The primary reason tomatoes don’t turn red is extreme temperatures below or above the optimum range of 66-77°F, affecting the pigmentation process. Overgrown branches spend most of the plant’s energy and can also prevent the tomatoes from ripening on the vine.

High temperatures 

Depending on the variety, tomatoes ripen from dark green to light green to red, yellow, pink, and orange. Temperature affects the production of the hormones lycopene and carotene responsible for pigmentation or color change. 

For pigmentation, temperatures must be between 66-77°F. Constant temperatures above 85°F make pigmentation difficult. Consequently, the tomatoes will start looking yellowish-green or orange.

Cold temperatures or cold drafts

Low temperatures below 50°F prevent tomatoes from turning red. As mentioned earlier, tomatoes ripen at temperatures of 66-77°F. Extremely low temperatures below 50°F affect pigmentation since no lycopene forms. 

You’re growing the wrong variety for your location

Tomatoes cultivars take different times to mature and ripen. If you plant a tomato variety that takes more time to ripen, it won’t even if the growing season is ending. The tomato plant will need more time to turn red.

 If summer is ending and a cold draft is approaching, but tomatoes aren’t red yet, check the variety against the ripening time.

Note: Tomatoes have short and long growing seasons. Short-growing season tomatoes mature within 50-60 days from transplant, while longer-growing season tomatoes take up to three months. The tomatoes take 20-30 more days to change color.

Stress from overgrown vines

Stressed tomatoes with overgrown vines don’t turn red since they use almost all their energy to develop new leaves or flowers.

These are also characterized by low yield that results from the overgrowth spending most of the plant’s energy instead of putting it into flowers and fruit.

Overfeeding your tomatoes

Excessive fertilizer does more harm than good. This article by Mississippi State University reports that high nitrogen and low potassium concentrations from fertilizer can lead to no color change since the plant uses the excess nutrients to grow greener foliage instead of pigments.

How to turn green tomatoes red on the vine

There is nothing more stressful than having your tomato plants not ripen. Below are my best fixes for turning green tomatoes red:

1. Cover the tomato plant

If your tomatoes aren’t ripening due to low temperature, protect them from the cold using row covers, old bedsheets, or a plastic tarp. 

But there’s a catch. The temperature must be 50-55°F to turn the green tomatoes red using a cover or plastic tarp. Otherwise, the tomatoes will ripen with soft spots and odd shapes.

Tomatoes never ripen on the vine if the night temperature is below 50°F while the daytime temperature is below 60°F.

2. Grow the correct variety in your area

Plant a tomato variety that has a similar growing period as the season in your area to make them ripen on the vine.

Before purchasing your tomato seeds or transplants, check the variety to confirm how long it takes to mature and ripen and choose one that matches the period before the first frost in your area. Growing the right variety ensures they ripen before the first frost.

Examples of short-growing season tomatoes to add to your garden include the early bird (hybrid), stupice (heirloom), and glacier (heirloom).

You might also want to find out if you’re growing determinate or indeterminate varieties of tomatoes.

3. Prune overgrown branches or vines

Cut overgrown branches or vines to unburden the tomato plant. Pruning prevents blossoming; thus, the tomato plant will concentrate its energy on reddening. Additionally, pruning encourages airflow, protecting the fruits from diseases.

Cut the overgrown branches with a pair of shears or scissors.

4. Fertilize tomato plants with enough fertilizer

Tomatoes need fertilization at most three times when they are actively growing. Applying enough fertilizer makes the plant grow leaves, flowers, and fruits and ripen at the right time.

You may be overdoing it if you use organic fertilizer options like coffee grounds to supplement vegetables with nitrogen. Excessive feeding can also cause too much foliage and overgrowth, leading to tomatoes not ripening.

5. Give your tomatoes more time

Turning a green tomato red due to hot temperatures is complex. Wait a little more for about two weeks to let temperatures drop to 68-77 degrees Fahrenheit for effective pigmentation.

FAQ

If there’s a frost approaching in a few weeks and your tomatoes aren’t ripe yet, pick the light green tomatoes and ripen them indoors. Also, pick light green tomatoes when temperatures exceed 85°F.

Pro tip: Pluck the tomatoes leaving a little stem where the fruit is attached to prevent them from decaying.

Bring your tomatoes indoors and store them inside boxes in a well-ventilated room at a temperature of 55-70°F. Your pantry area is an ideal storage room.

Let the tomatoes ripen in about 14 days, after which they’ll be ready for use. Remember to check them often while waiting to remove those spoiled from the good ones.

Caution: Don’t refrigerate mature green tomatoes to make them red. Essentially, a refrigerator has low temperatures below 40°F that discourage pigmentation. Besides, I find that tomatoes ripened in a refrigerator have a funny taste.

Conclusion

Tomatoes may fail to turn red when lycopene is not produced. If your tomatoes don’t turn red, check the temperatures to confirm they are within 66-78 degrees Fahrenheit.

Extremely low or high temperature is the most common reason tomatoes don’t turn red. Be sure to plant the right variety and feed the plant correctly.

To turn tomatoes red, fertilize them three times in the growing season. Cover them with row covers or old bedsheets when temperatures drop.

For extremely low or high temperatures, harvest mature light green tomatoes and ripen them indoors by storing them in a well-ventilated room with temperatures of 55-70 degrees Fahrenheit.

References

• The University of Maryland Extension: Growing Tomatoes in Home Garden.
• The University of Missouri: Hot Weather Tomato Problems.