How Much Light Does Lettuce Need to Grow Indoors (This much!)

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How Much Light Does Lettuce Need to Grow Indoors
How Much Light Does Lettuce Need to Grow Indoors (This Much!) –

Lettuce is quick to grow, easy to harvest, and comes in a gratifyingly broad range of sizes, colors, shapes, and textures. The big question with growing lettuce indoors is its light requirement. And one of the questions is how much light does lettuce need to grow indoors?

Lettuce needs at least 6.5 mol m–2 d–1 of photosynthetic light to grow lettuce indoors, according to research. However, 9.7 mol m–2 d–1 would be preferable to increase growth, nutritional attributes, and visual appeal. In addition, daily light integrals below 6.5 mol m–2 d–1 could significantly compromise the growth and quality of lettuce.

Moreover, growing lettuce could save you a lot of money. Usually, lettuce is inexpensive, but if you like salad as much as I do, you’re in for a problem.

  • Do you want to enjoy fresh lettuce without the hassle of digging for soil?
  • Would you want to have clean lettuce at your fingertips anytime?
  • And, don’t know how much light does lettuce needs to grow indoors?

Read on to find out everything you need to know about successfully growing lettuce indoors.

See also: Difference Between Hydroponics And Soil Gardening: Pros & Cons of Both.

How Much Light Does Lettuce Need to Grow Indoors?

Lettuce needs between 12 to 20 hours of daylight, showed a study by Ohio State University‘s Department of Horticulture and Crop Science.

Eight hours is the minimal quantity of daylight required for strong leaf growth, according to a trial study conducted in 2019 at Ohio State University.

See also: Everything You Need Before Starting Green Beans Indoors

How Long Does It Take for Lettuce To Grow?

After you plant your lettuce, it takes 7 to 14 days for lettuce to germinate (a week at 50 F and 2 days at 70 F), according to Cornell University. In addition, lettuce is generally a full-sun vegetable and will germinate and grow more quickly if you provide it with as much daylight as possible. However, lettuce will also tolerate partial shade and may even benefit from it throughout warmer weather.

While you may be wondering how much light lettuce needs to grow indoors, there is one more thing you need to think about, which is how long it takes for lettuce to grow indoors. Lettuce grows fairly quickly, but growing them indoors differs due to various factors, including how much light is available, so the question may arise again of how much light lettuce needs to grow indoors.

Lettuces are delicate and hence require extra care and attention when grown indoors. Once your tiny plants grow their first set of leaves, start feeding them with nutrition and also monitor the water intake so lettuces can grow steadily and are not waterlogged.

Cut only what you need because lettuce is perishable after trimming, leaving the remaining leaves to grow for a few days longer.

See also: Will Vinegar Actually Kill Crabgrass? Here’s The Truth!

How to Germinate Lettuce Seeds in Summer?

Lettuce seeds will germinate at 35°F; however, optimum germination is 70 to 75°F, according to North Carolina State University. If you provide lettuce with enough hardiness, it will withstand freezing. Lettuce has a relatively high water requirement, so soil moisture deficiency will seriously stunt growth and head quality. Irrigation dramatically reduces the risk of crop failure.

Whether you are sowing directly or transplanting your lettuce, it is important to keep the garden soil evenly moist. Plant a few seeds every 7-10 days; salad usually doesn’t last long in hot climates.

If you want to enjoy fresh lettuce every week, start with a small number of plants every 7-10 days. They tend to turn up the heat before they form a thorn, so instead, just harvest the lettuce as a delicate green. When they’re only 4 “tall, cut the leaves off about 1” off the ground. 

Stumps cut off from young plants often produce a different crop. Harvest the lettuce early in the day For the sweetest greens, harvest the lettuce early in the morning.

Studies have shown that lettuce leaves contain more than twice as many natural sugars at the beginning of the day as they do in the afternoon.

Tips On Germinating Lettuce Seeds in Summer:

  • Choose a well-drained area in your garden that gets about 4 to 6 hours of the morning sun but is also preserved from hot afternoon sunlight to help reduce soil temperature.
  • Prepare 1 to 2 inches of compost into the top 6 inches of soil.
  • Plant the seeds 1/4-inch deep and 6 inches aside in rows set 12 inches apart.
  • Gently mist the soil daily with water, so it remains moist.
  • Water your lettuce plants once or twice weekly so the top 6 inches of soil remain moist.
  • Keep the soil evenly moist when transplanting your lettuce; water your seedlings for 24 hours before transplanting, again 1 hour before, and immediately after planting in the outdoor garden. This will help reduce the stress of the transplant. 
  • You can even put a layer of ice on the ground right after planting the lettuce seeds outdoors in very hot climates. In the afternoon, shade your lettuce plants either on the east side of a building or in the shade of larger plants. You can protect them at 40%, too. Just make sure you lift the shade cloth to allow enough air to circulate the plants. 

Lettuce Germination Temperature 

Lettuce is a cool-weather crop, thriving best in the spring and fall. Cornell University states that lettuce grows best at temperatures in the range of 60 to 65 degrees Fahrenheit. However, the exact month will differ, depending on how warm your climate is.

Lettuce germination temperature depends on how much light is available for lettuce to grow indoors. You may contemplate how much light lettuce needs to grow indoors.

The answer to this question varies due to different weather conditions and various varieties of seeds present. Lettuce adapts to cool growing conditions with optimal growing temperatures of 60 to 65 ° F. At 70 to 80 degrees F, the plants will bloom and produce seeds. 

However, repeated exposure to freezing temperatures can seriously damage or kill crops.

See also: What Gardening Tools Do You Really Need to Start a Garden?

What Is The Best Time to Plant Lettuce?

The best time to plant lettuce is in early spring or late summer. At high temperatures, growth is small, the leaves may be bitter, and the seed stalks too elongated. Some varieties and types of lettuce resist heat better than others.

What Are The Most Common Types of Lettuce?

Lettuce is a reasonably hardy, cool-weather vegetable that flourishes when the average daily temperature is between 60 and 70°F.

There are five distinct types of lettuce

  • leaf (aka looseleaf)
  • Cos or romaine
  • Crisphead
  • Butterhead
  • And stem (aka asparagus lettuce or celtuce)

See also: Best Insecticide for Japanese Beetles: A Complete Guide

What You Will Need To Grow Lettuce Indoor:

  • Flats or shallow pots filled with potting mix
  • Slow-release fertilizer
  • Light source.
    • Natural light: a south-facing window with enough light works; however, your plants will be leggy.
    • Artificial light: You can also use a grow light ( here is a link to purchase one on Amazon)

See also: Fertilizer Vs. Plant Food: Are They The Same

How to Grow Lettuce Indoors?

There is nothing quite like the taste of freshly-picked greens straight from the garden. For most of us, this is a treat for spring through autumn. Well, you need not worry now. These lettuce-growing tips will keep your kitchen and salad bowl full of crisps all year long.

Growing lettuce in a garden is not difficult, but growing them indoors is a luxury we all want and need in our life. Having your fresh salad bar year-round is a delightful feature to have in your house. 

Here’s how to grow lettuce indoors:

  • Load your containers with potting mix, scratch fertilizer into the top 2 inches of the mixture, and spread seeds across the surface.
  • Ensure that they are in contact with the mix because lettuce needs light to germinate (don’t bury the seeds)
  • Put containers under the lights and adjust until the lights are about two inches above the containers.
  • Lettuce grows better in cooler temperatures, so avoid areas near heat vents that circulate hot air.
  • As seeds germinate and seedlings grow tall, keep adjusting the lights higher, about two to three inches above plant tops.
  • Keep watering your containers by spraying the water on the container surface to keep seeds hydrated until they sprout.
  • Every week, add diluted water-soluble fertilizer to the water.

See also: An Ultimate Guide To Successfully Start Cucumbers Indoors

Best Lettuce to Grow Indoors

Names Days to
pH Seed Per
100 Feet
of Row
Little Gem (romaine)606.0 to 6.71/16 oz
Parris Island (romaine)606.0 to 6.71/16 oz
Buttercrunch (butterhead)656.0 to 6.71/16 oz
Bibb (butterhead)606.0 to 6.71/16 oz
Red Sails (leaf)606.0 to 6.71/16 oz
Black Seeded Simpson (leaf)506.0 to 6.71/16 oz
Deer Tongue (leaf)506.0 to 6.71/16 oz
Salad Bowl (leaf)506.0 to 6.71/16 oz
Ruby (leaf)456.0 to 6.71/16 oz
Grand Rapids (leaf)456.0 to 6.71/16 oz
How Much Light Does Lettuce Need to Grow Indoors (This Much!) –

Common Issues With Growing Lettuce

Tipburn is a physiological condition causing lettuce to “dieback” at the edge of the leaves. It results from a calcium deficiency at the early stage, rapidly growing tissue at the edge of the leaves.

However, frequent and light watering and liming the soil to help raise the pH will help prevent tipburn.

Common DiseasesPestsOther
– Damping-off
– Fusarium
– Mosaic
– Downy mildew
– Aphids
– Leafhoppers
– Leafminers
– Wireworm
– Cabbage loopers
– Slugs
– Cutworms
– Tipburn (lack of calcium or irregular moisture)
– Bolting
– Leaf rots due to soil or moisture on leaves
– Bitterness due to lack of moisture or high temperature
How Much Light Does Lettuce Need to Grow Indoors (This Much!) –

See also: Aeroponics vs Hydroponics: Which one should you choose?

Final Thoughts

Now that you know the answer to how much light lettuce needs to grow indoors, you might as well start planting and enjoying your favorite lettuce at home.

If you love salads as I do, you can grow lettuce indoors all winter long. Just ensure you have enough light for lettuce.


Hello friends, I am Altiné. I am SO excited you are here! I am the guy behind Plants Heaven is a blog that shares information about preparing, creating, and maintaining gardens in and out of your home, regardless of where you live. My goal is to help you learn to love gardening and reap the benefits that come with it. I am still learning; therefore, the information I share on this site may not always be “expert” advice or information. But, I do my VERY best to make sure the information shared on this blog is both accurate and helpful.

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