Your tomato plants have grown into tall vines, flowered, and produced fruit, but it isn’t ripening quite the way you hoped. This might not be a cause for concern, and there may be a way to solve the problem.
So, why are your tomatoes not ripening? The tomato ripening process slows down or stops in extreme temperatures. Temperatures above 85 degrees Fahrenheit (29 degrees Celsius) or below 40 degrees Fahrenheit (4 degrees Celsius) will inhibit ripening of tomatoes.
Of course, there are other reasons that can cause tomatoes to ripen slowly or unevenly.
In this article, we’ll talk about why your tomatoes are not ripening. We’ll also talk about ways to solve the problem, even if a frost is approaching.
Let’s get started.
Why Are My Tomatoes Not Ripening?
“Ripening and color development in tomatoes is governed primarily by two factors: temperature and the presence of a naturally occurring hormone called ethylene.”
https://www.purdue.edu/hla/sites/yardandgarden/tomatoes-not-ripening/
Let’s start with temperature – an extreme in either direction can cause trouble for tomatoes in the ripening stage.
Tomatoes Not Ripening Due to Extreme Temperatures
Both high and low temperatures can prevent tomatoes from ripening or slow down the ripening process. Unless you planted very late in the season or live in a cold climate, high temperatures are the more likely culprit.
Tomatoes Not Ripening Due to High Temperature
As the sun sends down stronger rays and the summer heats up, the tomato ripening process can slow down. Temperatures above 85 degrees Fahrenheit (29 degrees Celsius) will cause tomatoes to ripen slowly (or stop ripening altogether!)
At these temperatures, tomatoes are less able to produce the pigments lycopene and carotene. These two pigments give tomatoes their deep red color.
When tomatoes produce less of these pigments, the skin may get stuck at a light red, pink, orange, or yellow color. In extreme cases with extreme heat, the tomatoes may remain green for some time, even after reaching full size.
Don’t worry though – if the summer heat is too much for your tomatoes and is causing a failure to ripen, you have some options (more detail on this later in the article.)
High temperatures can also cause tomato fruits to develop tough skins.
You can see my illustration of ideal temperature ranges for tomato plants here.
Tomatoes Not Ripening Due to Low Temperature
On the other hand, low temperatures at the end of the season can slow or stop the tomato ripening process. As winter approaches and cold weather looms, the race is on for tomatoes to ripen before the first frost date.
According to the Colorado State University Extension:
“Extended exposure to cool temperatures interferes with ripening and flavor development … temperatures of 40 degrees are too cold to ripen mature green tomatoes and are colder than desired for ripe ones.”
https://planttalk.colostate.edu/topics/vegetables/1844-ripen-green-tomatoes/
If you are getting nervous about frost ending the growing season before your tomatoes ripen, there are some ways to force Mother Nature’s hand (we’ll talk more about this later in the article).
What Causes Uneven Ripening of Tomatoes? (Stripes, Streaks, or Spots on Fruit)
Sometimes, a tomato will ripen partially. One part will be orange, pink, or deep red, while other parts will be yellow or green.
Chlorophyll is what makes tomatoes green when the fruit first appears. The pigments lycopene and carotene are what make the fruit turn red or orange.
When chlorophyll is not uniformly replaced by lycopene and carotene, we sometimes see green or yellow unripe stripes, streaks, or spots on the fruit.
A nutrient imbalance is one possible cause of uneven ripening in tomatoes. According to the Mississippi State University Extension, too much nitrogen (N) or not enough potassium (K) can cause uneven ripening.
Some tomatoes are green when ripe, such as the Green Zebra variety. Others will have a different skin color when ripe, such as purple tomatoes.
Why Are My Tomatoes Not Ripening On The Top?
Sometimes when we hear about uneven ripening of tomatoes, we think of the green “shoulders” (ridges) on top of larger heirloom tomato varieties.
It seems like a mystery – why would the bottom and sides of the fruit ripen up nicely to a deep red, while the “shoulders” of the fruit stay green?
However, when we think it through, it makes perfect sense. Remember that high temperatures can prevent tomatoes from ripening.
In the height of summer, the sun beats down on tomato plants all day long. The tops of the tomatoes get most of the sunlight, so they heat up more so than the rest of the fruit (that is, the bottom and sides stay slightly cooler than the top).
This temperature difference could account for the lack of ripening on the top of the fruit while the bottom and sides ripen up nicely.
Do Tomatoes Need Sun to Ripen?
Tomato plants do need sunlight to grow, as I explain in my article here. However, tomatoes do not need sunlight to ripen!
Tomato plants use sunlight to produce energy via photosynthesis. Once they produce and store enough energy, it is a matter of sending it to the fruit so that they can reach full size.
Once the tomatoes reach full size, they will begin to ripen as long as the temperature is right. If it is too hot, the ripening process will slow down or stop.
Since too much sunlight can heat up the fruit on a tomato plant, it might be necessary to provide some shade for your plants later in the season to encourage ripening of the fruit.
Whatever you do, don’t prune off all of the leaves in an attempt to provide more sunlight! According to the Cornell University Extension, sunlight does not have much to do with ripening once the fruit is fully formed.
In fact, too much strong sunlight can cause sunscald of the fruit, even if it doesn’t prevent ripening.
How to Get Tomatoes to Ripen
Maybe it is too hot or too cold for your tomatoes to ripen, or maybe you just want to speed things up.
Either way, there are some ways to get tomatoes to ripen. So, what are the best ways to turn green tomatoes red?
Your approach will depend on whether they are still on the vine or not.
Do Tomatoes Ripen Faster On Or Off The Vine?
“When the tomato reaches the breaker stage, when it is about half green and half pinkish-red, a layer of cells forms across the stem of the tomato sealing it off from the main vine. When this occurs, there is nothing that can move from the plant into the fruit.”
https://www.johnson.k-state.edu/lawn-garden/agent-articles/vegetables/harvest-ripen-tomatoes.html
At that point, it is up to the tomato fruit itself to ripen. The plant cannot help it any more at that point, since it cannot send any more nutrients, hormones, or pigments to the fruit.
So, once a tomato reaches the breaker stage, there is no advantage to leaving it on the vine to ripen. You can leave it on if you want, but if a frost is threatening, pick the tomatoes and let them ripen off the vine (more on this later).
How to Get Tomatoes to Ripen On the Vine
There are a couple of ways that you can help your tomatoes to ripen faster when they are still on the vine.
Keep the Tomato Plant Cool
In the summer heat, it might be difficult to keep your tomato plants cool, but it’s worth a shot.
For one thing, you can use shade cloth to provide some shade and keep your tomato plants cooler. This mesh-like material blocks out some sunlight, and can keep plants up to 10 degrees Fahrenheit cooler.
This shade cloth from Gardener’s Supply Company can be used with hoops for support.
Also, avoid pruning branches and leaves off of the plant. Any pruning will allow more sunlight to hit the fruit, which will cause it to heat up and reduce ripening.
This strategy is better suited to the summer, when temperatures are still high.
Cull Some of the Tomatoes
The other half of the tomatoes will then have a better chance of getting to the breaker stage, since the plant can concentrate its energy on fewer fruit. This strategy is better suited to the fall, when temperatures have started to drop and you need the fruit to ripen before frost.
Pull Up The Whole Plant
As a last resort, you can pull up the entire tomato plant and bring it indoors, as long as it is not too tall. This will be necessary if the tomatoes have not yet reached the breaker stage (described earlier).
If the tomatoes have reached the breaker stage, you can cut off the vine holding the fruit and bring it indoors. This will allow the tomatoes to ripen “on the vine” (but off the plant!).
How To Get Tomatoes To Ripen Off The Vine (After Picking)
Sometimes, you just have to pick your tomatoes before they are ripe, either because of a looming frost or because pests are ruining your season.
In that case, you can get your tomatoes to ripen by keeping them close. Put them all together in a bag and wait.
As the tomatoes release ethylene gas in a closed space, they will cause each other to ripen.
What To Do With Tomatoes That Don’t Ripen
Of course, you might have tomatoes that don’t ripen for whatever reason, despite your best efforts. In that case, you can try some of the following recipes:
Conclusion
Now you know why your tomatoes are not ripening. You also know a few ways to solve the problem, whether the tomatoes are still on the vine or not.
Remember to be patient – if your neighbors have fast-maturing tomato varieties, then their fruit will ripen before yours.
Keep track of your planting dates and days to maturity so that you know when to start worrying about slow ripening.
You might like to read my article on when to pick tomatoes (to optimize for ripeness).
You can learn more about why tomatoes flower early in this article.
You might also want to read my article on how to make tomato plants produce more fruit.
I hope you found this article helpful. If so, please share it with someone who can use the information.
If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here. Enjoy!
~Jonathon