Tomatoes are one of the most common produce items in the American home garden.
While the plant grows well in many climate zones, the fruit is sensitive to cooler temperatures, and you may find yourself needing to harvest your crop before the tomatoes are ripe.
The best way to ripen your tomatoes is to keep them on the plant, unless your climate does not allow for a mild, consistent development phase. If you are unable to keep them on the plant, bring them inside, keep them out of the sun and at room temperature, and place them in ventilated storage (like an open cardboard box or on newspapers) where they do not touch.
Either way, you can successfully ripen your tomatoes as long as they have begun to change color on the plant.
How Tomatoes Ripen
First, you must understand how tomatoes ripen. Once you understand what happens behind the scenes, you can manipulate the process.
The Ripening Process
Ripening is triggered when ethylene is introduced into the development process, and the plant’s cells respond by entering the breaker stage (source). The plant then forms a cell wall that blocks the stem from nourishing the fruit, which means the tomatoes no longer need the plant to continue ripening (source).
Once this happens, the fruit starts developing white streaks (the mature green stage), and then color.
Color changes will happen even if your tomato variety is green when ripe. Most varieties will be a light green before the ripening stage, and will at least change hues or develop stripes when the breaker stage begins. Watch for color changes to radiate out from the tops and bottoms of the fruits.
How Lycopene Influences Ripening
Lycopene influences tomatoes that turn red, orange, and yellow when they ripen. Lycopene is a pink/red pigment in tomatoes, watermelons, and similar fruits, and it has been linked to lowering the risk of strokes and certain cancers.
As the color changes, you are actually watching lycopene develop (unless you are growing a green or white variety).
This red color development is dependent on temperature. Lycopene develops best in mild temperatures between about 65⁰-80⁰ (source). If tomatoes are kept in proper, consistent conditions, this pigment should develop fully and evenly.
How to Ripen Tomatoes On The Vine
The ideal way to ripen tomatoes is on the vine.
Although you can replicate the ripening process by recreating favorable conditions, nothing matches the flavor and nutrient content of a vine-ripened tomato.
Temperature and Sun Exposure
Keeping the tomato connected to the plant is the best way to ripen them if the weather allows for it.
In milder, even-tempered climates, sun exposure will benefit the fruit by encouraging sugar production, although sunlight is no longer necessary for the fruit development. Tomatoes ripen best on the vine when the temperature hovers around 75⁰, which helps the tomato reach its peak flavor.
At around 86⁰, the red color stops producing as efficiently, and tomatoes that should be red can be yellow or orange. In areas where summer temperatures regularly exceed 90⁰, sun exposure can heat the fruit too much, which can halt the lycopene production or damage the fruit.
Sun-damaged tomatoes will be tough, leathery, and discolored with spots. They may eventually begin to rot.
To combat the effects of hot temperatures, research which tomato varieties do well in your climate. You can also consider putting your plants in containers so you can transfer them to cooler places if necessary.
In our article Ultimate Guide to Watering Tomato Plants (link), we cover why consistent, at-the-root watering is vital for tomato plants. Thorough watering 2-3 times per week is essential for proper fruit development.
However, once the fruit hits the breaker stage, it is no longer dependent on the plant. Watering at this stage is more for plant health. If your plant is not healthy enough to support the weight of the fruit, the fruit could sink to the ground or fall off the plant, which increases the risks of insect damage and rot.
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How to Ripen Tomatoes Off The Vine
The most common reason gardeners ripen tomatoes off the vine is because of impending inclement weather.
Generally, this is due to an upcoming frost or freeze that may kill the plant or damage the fruit if they are left on the vine. However, you may also choose to ripen your tomatoes off the vine if you live in an extremely hot, dry climate and your tomatoes are rotting or splitting instead of ripening into a firm, juicy fruit.
To ripen your tomatoes off the vine:
- Keep them at room temperature
- Do not expose them to direct light
- Keep them ventilated
- Encourage ethylene production (cover tomatoes with newspaper or place near apples)
- Remove rotting tomatoes immediately
When to Harvest
Tomatoes can be picked as soon as the breaker stage begins. Before reaching this stage, tomatoes will be firm and solid green.. Once the color begins to change, or stripes appear on the fruit, you can pick them for ripening indoors.
Wash fruits and throw away any with cracks or spots.
Then, sort the fruits into similar color categories (put the mature green tomatoes together, the blush tomatoes together, etc.).
At this point, the general rule is to not let the tomatoes touch each other and to keep them ventilated. You can store them on newspaper sheets or in open cardboard boxes- preferably in single layers.
If you want to keep the fruits on the plant, you can uproot the entire plant and store it in a room-temperature area. Although this isn’t necessary, it can help prevent rot while the fruits ripen.
Temperature is one of the most important aspects of successful ripening. If the fruits are too cold in storage, they will not ripen quickly enough and the fruits could go bad. If the fruits are too warm, the lycopene could form too quickly, and the fruits could look ready before the sugar develops.
Store the tomatoes at room temperature, or between about 65⁰-75⁰.
Mature, green tomatoes can be kept as low as 55⁰, but no lower. Once color appears, move them to a warmer area.
Temperatures below 50⁰ will kill the ripening enzymes and slow the flavor/color production, so do not store them in the refrigerator.
Do not expose green fruit to direct light. Once fruit begins to develop lycopene, you can move them into an area with indirect natural light to promote sugar development, but make sure fruit remains at room temperature.
Fruits ripen when they are exposed to ethylene. Other ripe fruits, like bananas and apples, produce ethylene gas that can encourage the ripening process in tomatoes.
You can also cover green fruits with a light layer of newspaper. This will trap ethylene gas without hindering ventilation.
When fruits are nearly ripe, remove the newspaper and other sources of ethylene or else the tomatoes may become overripe and rot before you can use them.
Why Won’t My Tomatoes Ripen?
If your tomatoes refuse to ripen, the most likely culprits are poor ventilation and lack of temperature control.
Unfortunately, some of the more common advice for ripening tomatoes can lead to these exact conditions. Don’t follow advice that results in lack of air circulation or recommends temperature extremes:
- Place your tomatoes in plastic bags: Plastic will trap ethylene without allowing air to circulate. Ultimately, tomatoes stored in plastic bags will rot before they ripen.
- Keep your tomatoes in the sun: This is often recommended because it will result in a color change. However, premature color development can halt true ripening, and the fruit may not have time to increase sugar content. Wait until the color begins to change naturally before you place the fruit in indirect natural light.
- Store your tomatoes in cooler temperatures: Cool temperatures kill the ripening enzyme, so make sure your tomatoes stay above 55⁰.
- Seal the box where you store your tomatoes: This will trap ethylene and encourage rot and mold.
For more information on growing healthy tomato plants, please read (link to tomato watering article). For more information on building a healthy soil profile to support a bountiful tomato harvest, read Soil Conditioner vs. Compost.