Do Tomato Plants Need Full Sun?

All plants need sunlight to grow but it’s particularly important for tomatoes. Without adequate light, your tomatoes won’t ripen—they might not even produce fruit at all. 

That brings us to the question, “How much light do tomato plants need?” And can they get too much sun? As with many things in gardening, balance is key. Insufficient sunlight can prevent your tomato plants from thriving but too much light can cause sun scald.

To put it simply, tomato plants need full sun. If you’re wondering what that means and how to find the perfect place in your garden for them, you’ve come to the right place. Let’s dive in!

3 Reasons Tomato Plants Need Full Sun

Where you plant your tomatoes makes a big difference, especially when it comes to sun exposure. Tomato plants need to be planted in full sun—a spot that gets at least 6 hours of direct, unobstructed sunlight per day. Here’s why:

1. To Grow and Mature

Sunlight is a plant’s primary source of energy. It’s a crucial ingredient for photosynthesis, the process through which plants convert carbon dioxide and water into sugar (food) and oxygen. Without adequate sunlight, tomato seedlings won’t grow the strong, healthy vines they’ll need later to support fruit. 

Getting at least 6 hours of direct sunlight per day is essential during the first 4-6 weeks after your tomato seedlings have been transplanted. Growing healthy vines requires a lot of energy and nutrients, so the more sunlight your tomatoes get during this stage, the better.

2. To Produce High-Quality Fruit

Somewhere between 30–45 days after transplanting, your tomato plants should start to develop little yellow flowers. These flowers will eventually produce fruit, so sunlight is also very important at this stage. Depending on the variety, you should start to see fruit forming about 70–100 days after transplanting. 

Tomato plants need a minimum of 6 hours of direct sunlight to produce fruit but 8 hours is better. The extra energy will yield more tomatoes and they’ll be sweeter for it, too. 

Keep in mind that temperature comes into play during the ripening phase (about 30 days after the fruit forms). The ideal temperature for ripening tomatoes is 70–75℉. When daytime temperatures hit 85-90℉, green tomatoes may fail to turn red and flowers may fail to form fruit. Healthy leaves can help shade the fruit when temperatures soar—another reason sunlight is important during the early stages of growth.

3. To Help Prevent Disease 

Adequate sunlight can help protect your tomato plants against disease. Not only does it help your plants grow robust enough to withstand shifting conditions, but it enhances their ability to defend against pests and pathogens. When your tomato plants are weak, they’re more susceptible to pests and disease.

When temperatures drop overnight, dew collects on the leaves of your tomato plants. Exposure to morning sun helps dry the dew so it doesn’t keep the leaves wet, creating the damp and humid conditions that can lead to fungal diseases. Even UV radiation can have a mitigating effect on some fungal diseases.

How to Find the Perfect Spot to Plant Tomatoes

By now it’s been made clear that tomato plants need full sun. But do they need 6-8 consecutive hours of direct sunlight? Not necessarily. Many plants (including tomatoes) can benefit from exposure to both morning and afternoon light. Here’s why:

• Morning light helps dry dew on the leaves and initiates the process of photosynthesis for the day.
• Afternoon light helps prolong the day’s energy cycle to promote healthy growth and fruit ripening. 

The best place for tomato plants is a sunny spot with well-drained soil. If daytime temperatures in your area exceed 75℉, consider planting your tomatoes in a spot that gets afternoon shade. In cooler climates or areas where achieving a full 8 hours of sun might be a stretch, try to orient the plants in an east-to-west direction so they’ll have first access to morning sun.

Tips for Avoiding Sunscald

In gardening, you can have too much of a good thing, including sun. Too much direct sunlight can raise the temperature around your tomato plants too high for the fruit to ripen. It can also cause ripe fruit to crack, damaging your harvest. If there isn’t adequate foliage to shade the fruit, excess light could also cause sunscald. 

Here are some simple tips for avoiding sunscald:

• Leave adequate space between plants when transplanting seedlings to ensure proper air circulation so conditions don’t get too damp or humid.
• Monitor the daytime temperature around your tomato plants and make a plan to intervene if they regularly exceed 80℉. 
• Scale back on pruning while fruit is forming and ripening—the leaves can help shade the fruit to keep it from overheating or scalding.
• Consider hanging a white shade cloth over your tomato plants to help protect them from the heat without affecting their ability to absorb sunlight.
• Harvest your tomatoes early, as soon as they start to color, and let them finish ripening in a shady spot.

Sometimes it takes a growing season to figure out what problems you’re likely to encounter. Do what you can to preserve your harvest and take what you’ve learned to make adjustments for the next growing season.

Final Thought: Consider Starting Tomatoes Indoors

Starting tomato plants indoors might seem counterintuitive, given that there’s no sun inside. However, a sunny windowsill could provide sufficient light, and there’s always plug-in grow lights to consider. But what’s the benefit of starting tomato seeds inside?

You want your tomato plants to be as strong and healthy as possible by the time summer reaches its peak—that’s the best way to ensure a bountiful harvest. Starting seeds indoors means you can transplant your seedlings earlier, as soon as the danger of frost has passed. They’ll still need plenty of sunlight and regular watering, but they’ll have a healthy head start.

Start prepping for the next growing season now by stocking up on seed starting supplies. Shop the collection on Park Seed.