Tomatoes Not Turning Red

You’ve waited patiently, watching your tomato plants grow tall and produce loads of green fruit. But now, those tomatoes are not turning red. It’s a common frustration that can test any gardener’s patience. Understanding why this happens is the first step to getting the ripe, red harvest you want.

When tomatoes stay stubbornly green, it’s usually a sign that something in their environment is holding them back. The process of turning from green to red (or orange, yellow, etc., depending on the variety) is called ripening. It’s a complex biological shift triggered by the right conditions. Let’s look at the main culprits and how to fix them.

Temperature: The Biggest Reason for Green Tomatoes

Heat is crucial for tomato ripening. The ideal range for the red pigment, lycopene, to develop is between 68°F and 77°F (20°C to 25°C). When temperatures stray too far from this, ripening slows or even stops.

Too Hot: Consistently temperatures above 85°F (29°C) can actually prevent lycopene and carotene from forming. The fruit may stay in a yellow-orange stage or just stay green.
Too Cold: When nights dip below 50°F (10°C), the ripening process grinds to a halt. The plant’s metabolism slows, and it focuses on survival, not fruit development.

If you’re in a hot climate, provide afternoon shade with a cloth. For cooler climates, choose early-ripening varieties next season and use black plastic mulch early on to warm the soil.

Variety Choice and Days to Maturity

Not all tomatoes turn the classic fire-engine red. Always check your seed packet or plant tag.

Color: Some varieties ripen to yellow, orange, purple, or even striped. Make sure you know what color to expect.
Days to Maturity: This number is from transplant to harvest. A ‘Brandywine’ (80-100 days) will take much longer than a ‘Early Girl’ (50-60 days). If you planted late, you might just need to wait a bit longer.

Nutritional Imbalances in the Soil

What you feed your plants affects everything, including ripening. An imbalance can cause problems.

Too Much Nitrogen: This promotes lush, green leafy growth at the expense of fruit production and ripening. The plant is too busy making leaves!
Lack of Potassium: Potassium is vital for fruit quality and ripening. A deficiency can lead to poor color development and uneven ripening.

Use a balanced fertilizer when planting, but switch to a fertilizer lower in nitrogen and higher in phosphorus and potassium once flowers appear. A simple soil test can give you the answers you need.

Overcrowding and Light Issues

Tomatoes need energy from the sun to ripen fruit. If they’re not getting enough, the process will be slow.

Dense Foliage: Overgrown plants create shade on the fruit. Good air circulation is also important.
Overcrowding: Planting to close together leads to competetion for light and resources.

Prune suckers (the shoots that grow in the leaf joints) on indeterminate varieties. Remove some of the older, lower leaves to let light and air reach the fruit. Always follow proper spacing guidelines for your variety.

Watering Stress: Too Much or Too Little

Inconsistent watering stresses the plant and can cause ripening problems.

Drought Stress: The plant will stop all non-essential processes, including ripening, to conserve water.
Overwatering: This can lead to root rot and nutrient uptake issues, which weakens the whole plant.

Aim for deep, consistent watering. The goal is about 1-2 inches of water per week, depending on your climate. Mulching heavily with straw or wood chips helps keep soil moisture even.

How to Prune for Better Ripening

Identify suckers on indeterminate plants (they grow between the main stem and a branch).
Pinch off small suckers with your fingers. For larger ones, use clean pruners.
Remove yellowing or diseased leaves from the bottom of the plant.
Thin out some inner leaves if the plant is very dense to allow light penetration.

The “Final Harvest” Trick: Ripening Indoors

As the season ends, especially if frost threatens, you can ripen green tomatoes indoors. They need to be at the “mature green” stage (full-sized, with a slight glossy sheen, and starting to turn pale).

Gently pick the tomatoes, keeping the stem attached if possible to prevent rot.
Wipe them clean and check for any bruises or damage. Use damaged ones quickly.
Place them in a single layer in a cardboard box or paper bag. Adding a ripe banana or apple can help. These fruits release ethylene gas, a natural ripening agent.
Store the box in a cool (60-65°F), dark place. Check them every few days and remove any that show signs of rot.
Be patient! It can take a few weeks for some to fully ripen.

Common Mistakes to Avoid

Planting to Early: Putting plants in cold soil stunts them and delays everything.
Ignoring Soil Health: Poor soil leads to poor plants. Amend with compost annually.
Over-fertilizing: More food is not always better. Stick to recommended amounts.
Leaving to Many Fruits: On late-season plants, consider removing tiny flowers and very small fruit so the plants energy goes into ripening the larger ones.

Prevention for Next Season

A little planning goes a long way in avoiding the green tomato dilemma.

Choose varieties with a “Days to Maturity” that fits your growing season length.
Warm your soil with black plastic mulch in early spring if you have short summers.
Get a soil test and amend your soil based on the results before planting.
Set up a consistent watering system, like a soaker hose, from the start.
Ensure your garden site gets a minimum of 6-8 hours of direct sun.

Frequently Asked Questions

Why are my tomatoes big but not turning red?

This is classic sign of temperature stress (too hot or too cold) or a nitrogen imbalance. The plant had enough energy to grow the fruit but not the right conditions to ripen it.

Will green tomatoes ever turn red?

If they are mature green tomatoes, yes, they can ripen off the vine using the indoor method. Very small, immature fruit likely will not.

What can I do with tomatoes that won’t turn red?

Don’t throw them away! Green tomatoes are delicious. You can use them for fried green tomatoes, green tomato chutney, salsa verde, or pickling.

Does picking tomatoes help others ripen?

Yes. Removing the largest, most mature green tomatoes can sometimes encourage the plant to focus it’s energy on ripening the remaining fruit.

How long does it take for tomatoes to turn red?

After pollination, it typically takes 6-8 weeks for fruit to develop and ripen. But this depends heavily on variety, temperature, and sunlight.

Seeing tomatoes not turning red can be frustrating, but it’s rarely a disaster. Most often, the issue is related to temperature, feeding, or simple timing. By checking these factors one by one, you can usually find the cause and take action. Whether you get them to ripen on the vine or finish them indoors, your patience will be rewarded. And remember, even a green tomato can be a tasty end to the season.