Lettuce Light Requirements – How Much Sun or Grow Light Does Lettuce Need?

If you want to grow lettuce plants at home, providing them with the right amount and type of light is key. This is true regardless of whether you’re growing lettuce indoors or outdoors.

Over the years, I’ve grown hundreds of lettuce plants both indoors and out. And I’ve learned a thing or two about how much light lettuce needs to thrive!

I’m going to share all you need to know about lettuce light requirements so you can grow healthy plants.

How Much Light Does Lettuce Need?

Lettuce plants thrive when they receive at least eight hours of bright light each day. However, they will grow best if they receive twelve or even fourteen hours of daily light.

This much light allows them to properly complete photosynthesis—the process in which plants use energy from the sun to convert carbon dioxide and water into sugar, oxygen, and water.

How Much Sun Does Lettuce Need?

If you’re growing lettuce outdoors, your plants will be relying on the sun for light. And this is just fine!

When you’re growing lettuce outdoors, you generally want to plant in areas that receive full sun. This applies to all types of lettuce, including romaine, buttercrunch, bibb, little gem, and baby lettuce mix.

Full sun is especially important in the spring, fall, and winter. This is because days are shorter during this time, and you want to make sure your lettuce has access to every bit of available sunlight.

During the summer, you may find that your lettuce plants benefit from a bit of shade or dappled light. If that’s the case, you can utilize companion planting and tuck lettuce beside tall plants like tomatoes and peppers. Another option is to use shade cloth.

How Many Grow Light Hours Does Lettuce Require?

If you’re growing lettuce indoors, you may be utilizing a grow light. Unlike with the sun, it is easy to set the exact number of hours of light a grow light provides.

The amount of light you provide each day will depend on the intensity of the grow light, how close the light is to the plant, and the number of hours the light is on each day.

There are numerous measurements used to refer to light, including watts and lumens. Watts refers to the amount of power a light consumes while lumens refers to the amount of light emitted during a given period of time.

Therefore, if you want to determine the brightness of light, you should look at the lumens. Generally, lights with fewer lumens will need to be on for more hours each day.

If you don’t know how bright your grow light is, it’s a good idea to start with 12 hours of light per day. You can always adjust this amount later down the line.

And if you’re looking for a grow light to use, this is one suitable option and this is another.

When Should You Use Shade Cloth for Lettuce Plants?

While lettuce plants enjoy lots of sunlight, sometimes intense heat coupled with direct light can be too much for these crops to handle.

If you’re growing lettuce outdoors in the summer, manipulating the environment can help prevent the lettuce from bolting (going to seed) and allow for a successful harvest. One easy way to do this is with shade cloth.

As the name suggests, shade cloth helps limit the sun’s intensity, making it more suitable for lettuce plants. Generally, lettuce plants can benefit from shade cloth if they are growing in sunny conditions above 85ºF.

Numerous types of shade cloth can work well, but I like to use a 50% shade cloth. This cuts the sun’s intensity in half.

To use shade cloth, start by inserting metal hoops or stakes above your lettuce plants. You can then drape the shade cloth over these supports—the cloth should not be touching the plants.

It’s important to note that limiting the light can lead to tender and less colorful plants.

I often cover lettuce seedlings with shade cloth for the first few weeks they are in the ground. Once they have adjusted to the heat, I remove the shade cloth and allow the plants to mature in full sun.

Can Lettuce Grow in Shade?

While lettuce can handle part shade, it will suffer if it is grown in full shade.

If lettuce plants don’t receive enough light, they may become stunted, weak, and susceptible to disease.

The following signs may indicate your plant needs more light:

  • Dull coloration; plants may appear off-white
  • Elongated stems and leaves that appear to be reaching for light
  • Stunted growth

With that said, lettuce plants will often benefit from afternoon shade in the summer. Planting them on the east side of taller plants like tomatoes or peppers will help provide shade.

Can Lettuce Receive Too Much Light?

Yes, lettuce plants can receive too much light! Too many hours of light as well as both light that is too intense can lead to damage.

Lettuce plants should not receive more than 16 hours of light during each 24-hour period. Additionally, you should ensure that lettuce plants are not suddenly exposed to intense light.

Light that is too bright may cause lettuce leaves to become “burnt.” This appears as white portions of leaves that may eventually die.

Do Lettuce Seeds Need Light to Germinate?

While some types of seeds require light to germinate, lettuce seeds do not. Planting them a quarter of an inch below the soil surface is the best practice.

However, once the seeds germinate, you’ll want to ensure you provide the seedlings with lots of bright and direct light. If you are growing seedlings outdoors or in a high tunnel, provide them with full sun. And if you’re starting seedlings indoors, place a grow light a few inches above the seedlings.

Photo of author

Briana Yablonski

Briana holds a B.S. in Plant Sciences from Penn State University and has been working with plants, soil, and ecology for over ten years. She spent five years working on vegetable farms throughout the East Coast before starting her own farm in 2020. She has been writing about plants, food, and science since 2019.

2 thoughts on “Lettuce Light Requirements – How Much Sun or Grow Light Does Lettuce Need?”

  1. Hello Briana,
    You didn’t mention anything about the required DLI for lettuce.
    I had an argument with someone and he claims that 5 mol/m2/day is enough to grow lettuce commercially.
    Is this true?!
    Looking forward to hearing from you.

    Reply

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