Tomatoes not ripening? Here are the four main reasons why your tomatoes aren't turning red, and what you can do (if anything) to help ripen your tomatoes.
Why do tomatoes turn red?
Tomatoes turn red because of their lycopene content. What is lycopene? From Web MD (emphasis mine):
Lycopene is a naturally occurring chemical that gives fruits and vegetables a red color. It is one of a number of pigments called carotenoids. Lycopene is found in watermelons, pink grapefruits, apricots, and pink guavas. It is found in particularly high amounts in tomatoes and tomato products. In North America, 85% of dietary lycopene comes from tomato products such as tomato juice or paste. One cup (240 mL) of tomato juice provides about 23 mg of lycopene. Processing raw tomatoes using heat (in the making of tomato juice, tomato paste or ketchup, for example) actually changes the lycopene in the raw product into a form that is easier for the body to use. The lycopene in supplements is about as easy for the body to use as lycopene found in food.
People take lycopene for preventing heart disease, “hardening of the arteries” (atherosclerosis); and cancer of the prostate, breast, lung, bladder, ovaries, colon, and pancreas. Lycopene is also used for treating human papilloma virus (HPV) infection, which is a major cause of uterine cancer. Some people also use lycopene for cataracts and asthma.
How does it work?
Lycopene is a powerful antioxidant that may help protect cells from damage. This is why there is a lot of research interest in lycopene’s role, if any, in preventing cancer.
So – no lycopene = no red tomatoes.
Reason #1 Your Tomatoes Don't Ripen = Time to Maturity
Each tomato variety has a time to maturity, i.e., days that it takes to ripen fruit from when the seed is planted. As a northern grower, I make sure to include some varieties that have a shorter time to maturity, along with some of the larger, longer season tomatoes. If we get a particularly bad year, the short season tomatoes may be the only ones to have time to ripen, but usually they are simply the first tomato plants to give me ripe tomatoes for the season. As the season progresses, more varieties ripen. Most tomatoes will ripen in six to eight weeks from when the blossoms are pollinated.
Some of my favorite short season varieties are:
Reason #2 Your Tomatoes Aren't Turning Red = Temps are Too Cold
We ran into this problem in the summer of 2014. The spring was cold and wet, and the summer was cold and dry. My friend, Tami, who busts her tail to start her seedlings early in her greenhouse and get them out in the garden as soon as absolutely possible, saw something she never saw before. Instead of getting red, her tomatoes stayed pink – but they rotted as if overripe. She harvested all the pink, soft tomatoes and made some very ugly tomato salsa, but the flavor just wasn't very good.
As the season progressed, the tomatoes that did ripen were bland and flavorless. I took to picking them as soon as they started showing the first blush of color and bringing them inside to fully ripen, because the nights were so cool. The peppers were the same way. Full size, but they stayed green until I brought them in to the counter, where they turned red in a couple of days.
Reason #3 Your Tomatoes Are Not Ripening = Temps are Too Hot
This year (2015), many area of the country are running into the opposite temperature extreme – it's too hot for the tomatoes to ripen. While tomatoes are generally heat loving plants, roasting heat is a problem. Cornell University Cooperative Extension notes:
The optimum temperature for ripening tomatoes is 70 to 75F. When temperatures exceed 85 to 90 F, the ripening process slows significantly or even stops. At these temperatures, lycopene and carotene, pigments responsible for giving the fruit their typical orange to red appearance cannot be produced. As a result, the fruit can stay in a mature green phase for quite some time.
What can you do if you're stuck with green tomatoes and intense heat? Once the tomatoes have reached mature size, you can bring them inside to finish ripening. Remember, tomatoes like it 70-75 F – just like many of us humans.
Never put your tomatoes in the fridge! With apologies to my husband's late great Uncle Bill, who worked on the railroad for many years and shipped tomatoes in refer cars – you don't store tomatoes in the refrigerator. Cold temps turns the sugars in the tomatoes to starch, ruining the flavor and making them mealy and bland. This is part of the reason many store tomatoes taste so bland. They are shipped in refrigerated trucks. They don't rot, but the flavor is subpar.
Reason #4 Your Tomatoes Aren't Turning Red – They're Not Red Tomatoes
With the growing popularity of heirloom tomatoes, there are many varieties now available that simply do not turn red, even when ripe. Tomatoes varieties may ripen to pink, orange, yellow, purple – even green. If you're trying a new variety of tomatoes, make sure you know what the mature stage is supposed to look like, so you don't miss out on the yumminess.
For instance, when I first tried garden peach tomatoes, I gave a plant to my mom. She didn't tell my stepdad what she was growing. He saw the thin skinned, lightly fuzzy tomatoes in the garden, and thought they were sick. He picked the ripe tomatoes and tossed them out. Mom went looking for her tomatoes and found them gone. They got it sorted out, but she had to wait a little longer to try the tomatoes.
Since I plant several different colors, I always note which plant is where on my garden charts. I also take care not to place plants that have similar size fruit but mature to orange and red next to each other, so I'm not mistaking underripe red fruit for ripe orange fruit.
How to Tell When Green Varieties of Tomatoes are Ripe
I've been growing Green Zebra tomatoes for a number of years, because the flavor is excellent and they usually produce a good crop here. As the name implies, they ripen green with stripes. As with other green varieties I've tried, you can tell they are ripe because the underlying color of the green tomato turns more yellow/golden instead of white/lighter green. The flesh will also turn soft and juicy.
Other Reasons For Strange Colored Tomatoes
Sunscald – Light colored, leathery patches, generally found on the top or side of the tomato may be sunscald, which is due to intense sun exposure. If not spoiled, the rest of the tomato may be used. Sometimes the scald leads to rot.
Soil Fertility Issues – Cornell University Cooperative Extension notes, “high levels of magnesium and low levels of potassium can lead to conditions like blotchy or uneven ripening or yellow shoulder disorder.”
Blossom End Rot – When the blossom end of your tomatoes has a small or large black lesion, this is blossom end rot. It's linked to low calcium availability in the soil, so adding calcium during planting may be helpful for avoiding it – BUT – even when there is calcium in the soil, too much or too little rain can make it unavailable to the plants. Regular, even watering is best. Read “7 Steps to Stop Blossom End Rot” for more on the causes of BER and how to prevent and control it.
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