If you have tomatoes that just won’t seem to turn ripe, you’re not alone. It’s not uncommon for tomatoes to be slow to ripen.
In fact, depending on the weather and depending on the circumstances, it is entirely possible for tomatoes to stop ripening altogether, even in the middle of the season.
There are some real explanations for why tomatoes sometimes stop ripening. Knowing why will help you to decide what to do about it.
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4 Reasons Your Tomatoes Aren’t Ripening
Temperature and weather are the big reasons why tomatoes don’t ripen on time. Often, that’s something you can manage. Most of the time, it’s a temporary issue and just a matter of time and weather turning to get your tomatoes ripening again.
Following here are the four most common reasons why tomatoes stop ripening when they should, and what you can do about it.
1. The temperature is too cold
Cool temperatures are a main reason why tomatoes ripen slowly or stop ripening. It’s all about ethylene gas production.
Ethylene is a gas that is naturally emitted by some plants and fruits during the ripening process. When the ambient temperature is too cold, tomato plants can’t produce ethylene gas well, and they need ethylene gas to ripen their fruit.
The ideal temperature is between 68 and 77℉ (20 and 25℃) for ethylene gas production, with a range of 70 to 75℉ (21.2 to 23.9℃) being even better. That’s the sweet spot, and when you drop down below 68 degrees (20℃), ethylene gas production slows. Much below 55 degrees (12.7℃), and ethylene production might shut down completely. Or, it may be very inconsistent, slowing the ripening process.
What you can do to speed tomato ripening in cool weather
- Cover plants with row cover fabric or clear plastic on cool days
- This helps to create a greenhouse-type warming effect
- The fabric or plastic will also hold heat in
- The cover will also help keep the ethylene gas produced closer to the plant and the tomatoes that need to ripen
- You can also pick off the green and underripe fruit and bring them inside to finish ripening
- Finishing inside may be the only option at the end of the season when temperatures do not stay warm enough for ripening outdoors
2. The temperature is too hot
Again, the ideal range for ethylene production is between 70 and 75℉ (21.2 to 23.9℃). When temperatures go above 75℉ (23.9℃), ethylene production suffers. At 85 to 90℉, it may stop, at least until the temperatures fall to more moderate temperatures again.
High temperatures are the main reason why tomatoes may start to ripen and then stop. Often, tomatoes will start ripening when the temperatures are moderately warm, and then a heat wave hits, and the fruit just stops changing color.
This is why you may see promising early development, and then it seems like it takes ages for the fruit to finish.
Fortunately, this is a temporary situation that will switch again when things cool down to more normal levels.
It is also a situation where you can step in to help the tomatoes along toward ripening.
What you can do to ripen tomatoes in hot weather
- Use shade cloth over the patch to lower the temperature around the plants
- Keep tomatoes watered at the base (hydrated tomatoes handle heat better and won’t be compromised by wilt or dried plant parts)
- Mulch the soil at the base of the plant to keep moisture in and to help cool plant roots
- Bring mature green and underripe fruit inside to a cooler space where they can ripen off the vine
3. The plants are overloaded with fruit
Can a tomato plant produce too much of a good thing?
Not really, but high-producing plants may be slower to ripen the bumper crop.
If your plants are producing prolifically, it will take longer for the tomatoes on that plant to ripen. The plant will divert energy to ripen the fruit, but there is a lot of fruit to ripen, and there is a limit to the plant’s energy that can be diverted. When a tomato plant has a lot of fruit on it that is ready for ripening, it simply takes longer to get all that energy to all those fruits.
This is an issue that we see more with determinate tomatoes than with indeterminate varieties. Determinate tomatoes set their fruit mostly all at once (or within a few weeks’ time), which means they end up with a lot of fruit on the vine ready to ripen in roughly the same amount of time.
Indeterminate tomatoes will continue to produce and grow, and they have fewer tomatoes on the vine that are ready for ripening at the same time. So the energy is being more evenly distributed in the plant, and only the ripe-ready tomatoes are getting the ripening energy expenditure.
This is one reason why you may see determinants growing tomatoes at the same time (or even later) as indeterminates, but the reason why those indeterminates may ripen long before the determinate varieties.
All of this said, if your indeterminate plants are having a bumper year and are slow to ripen, the abundance of fruit may be why it’s taking a while to get ripe tomatoes.
What you can do to ripen tomato-laden tomato plants faster
- Remove some of the tomatoes that are starting to turn, and let them ripen off the vine
- Take off some almost ripe green tomatoes and use them for green tomato recipes
- Make sure the tomatoes are well supported with nutrients and, most importantly, water, so the plant can access soil nutrients to support its energy needs
4. They have longer days to meet harvest requirements
Sometimes the problem is not the tomato plant at all, but our unreasonable expectations. Different varieties of tomatoes have different days to maturity. Sixty to 90 days is a common range, with some varieties being as low as 45 days, and some stretching as long as 100 or 120+ days.
It’s best to know how many days a tomato plant needs to reach maturity and ripening before you plant it. But if you’re not sure, and you think you should be seeing ripe tomatoes, check your label or look up the variety you’re growing. This should help you determine when the fruit should be ripe.
What you can do to ripen longer-day tomato varieties
- Check the days to harvest for the variety you planted to determine when the tomatoes should start to ripen
- Wait! You can’t make a 90-day variety into a 45-day variety. Have some patience and wait until the time is right for your tomatoes to ripen
Tips for Ripening Unripe Tomatoes Off the Vine
- Pick only tomatoes in the mature green or later stage to ripen off the plant
- It’s best to wait to see a blush of color before removing tomatoes from the plant
- Ripen tomatoes at room temperature
- Do not refrigerate tomatoes to ripen them; this will disrupt ethylene production and ripening just like cold temperatures outdoors will (and the taste and quality will degrade if you refrigerate tomatoes -- even ripe ones!)
- Ripening in a bag or cooler will speed ripening, as it will collect and concentrate the ethylene gas
- Adding another ethylene-producing fruit,l ike an apple or banana (or a couple if you have a lot of tomatoes) can help
- Bananas and apples both produce ethylene gas and can emit it to the tomatoes
