One of the delights of a summer vegetable garden is a luscious, ripe, red tomato. However, sometimes tomatoes don’t always do what we want. Tomatoes not turning red is a common vegetable garden frustration.
In general, the fruit on your tomato plant should begin turning red about 6-8 weeks after the flowers are pollinated. If this doesn’t happen, there could be several reasons why.
Factors such as heat extremes, incorrect pruning, too much nitrogen, and the variety of tomatoes planted can all contribute to the problem of tomatoes not ripening properly.
Keep reading to learn why your tomatoes are not turning red on the vine.
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Why are my green tomatoes not turning red?
Tomato ripening is triggered by a chemical called ethylene. This chemical is odorless, tasteless, and invisible to the eye but when the tomato reaches the green mature stage, it will start to produce ethylene and the tomato will begin to turn red.
When this doesn’t happen, other factors may be causing the delay in ripening. Let’s examine some of them.
Tomato types ripen at different times
The variety of tomatoes you plant determines when they will ripen and turn red. Not all types of tomatoes come to maturity at the same time; some have a delayed ripening.
Varieties that produce smaller fruit, such as patio and cherry tomatoes, will begin to ripen sooner than a larger variety such as a beefsteak tomato.
This is because larger tomatoes take longer to reach the green mature stage which is needed for the later red stage.
I planted both determinate patio tomatoes and indeterminate beef steak tomatoes this year, and my patio tomatoes grown in pots are almost done ripening, while the larger beef steak variety is just getting to the mature green stage.
The answer may simply be to have patience, if this is the reason why your tomatoes are staying green.
Heat extremes can delay ripening in tomatoes
Outside temperatures also play a part in the ripening of tomatoes. Tomatoes produce carotene and lycopene when the temperature is between 50°F and 85°F. (10°F and 29°F)
These substances are what cause tomatoes to turn red. This means when the temperature is colder than 50°F (10°C) or warmer than 85°F (29° C) your tomatoes will stay green.
These temperature extremes can not only keep tomatoes from ripening but also cause other problems such as tomato blossom drop, yellow leaves on tomato plants, tomato leaf curling, and low fruit set.
Too much sunlight delays the ripening of tomatoes
Although tomatoes need full sunlight to grow and produce fruit, too much sunlight can keep tomatoes from ripening.
My patio tomatoes were planted earlier in the year and had a chance to stay in the ideal temperature range. On the other hand, my larger tomatoes were planted later when there was more sunlight and heat which caused them to stay green.
Too much nitrogen can keep tomatoes green
While fertilizing tomato plants can give you a bumper crop, using the incorrect fertilizer or feeding plants too late in the season can delay the ripening of their fruit.
If you use a fertilizer high in nitrogen, it will encourage the tomato plant to divert energy into producing leaves instead of ripening existing fruit.
The timing of fertilization affects ripening too. As a general rule of thumb, when the plant starts to set fruit, it is time to cut back on fertilizing.
Too many tomatoes on a plant delay ripening
Sometimes, the reason for tomatoes staying green is that your plant has too much fruit growing at the same time. If this is the case, your tomato plant will have trouble ripening them all at once.
As hard as it is to do, pruning is the answer. If you remove about 1/4 of the tomatoes, the plant can concentrate its resources on ripening those that remain.
Pruning suckers early in the season can help tomatoes turn red later in the season. A tomato plant with lots of suckers along the stem is weak and stressed tomato plants will have trouble ripening.
Not all tomatoes turn red
Even though there are many legitimate reasons why tomatoes aren’t turning red, as we have seen, the culprit may be less obvious. Not all tomatoes turn red when ripe!
Some varieties, like “Yellow Brandywine” can be a bright yellow color, and others, such as “Purple Zebra” have red and green striped skin.
Some tomatoes are even meant to stay green. “Cherokee Green” is an heirloom variety that has a green-yellow skin when ripe with flesh that is also green.
Check the description on your seed package to give you an idea of what your ripe tomato should look like.
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