How to Grow Lettuce Indoors

Try your hand at indoor gardening with this easy crop

Containers of lettuce sit on a white windowsill.

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No need to splurge on organic lettuce from the supermarket - you can easily grow it yourself indoors all year round! Growing lettuce indoors is a great project for beginners or amateur gardeners as it yields quick results and requires little effort. In fact, lettuce is one of the easiest crops to grow indoors, and it can be continually harvested once it has reached maturity.

Botanical Name Lactuca sativa
Common Name Lettuce
Plant Type Leaf vegetable
Mature Size 4-6’ indoors
Sun Exposure Medium to bright indirect light, or partial shade (indoors), direct sun (outdoors)
Soil Type Fertile, well-draining
Soil pH 6.0 to 6.5
Bloom Time Summer and early fall
Flower Color Yellow
Native Area Mediterranean, Siberia, planted all over the world

How To Grow Lettuce Indoors

Lettuce is ideally suited to indoor gardening as it prefers mild temperatures and grows quickly. As with many herbs and vegetables, lettuce requires plenty of light and water in order to survive. Finding a good spot in your home with plenty of light is the key to growing this crop successfully inside. Before you begin growing lettuce, it is important to note that lettuce seeds do not keep well and old seeds may not germinate if planted so it is best to use fresh seeds for the highest chance of success.

Heads of lettuce with oil and vinegar on a white background.
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Light

At least 12 hours of light is required to grow lettuce indoors, with between 14 to 16 hours of light being ideal. Direct light is preferred as long as the growing location does not become too hot. Natural light can be supplemented with artificial grow lights, which may be necessary during the winter when the number of daylight hours is reduced. Yellowing leaves and thin, straggly stems are indications that your lettuce plant is not receiving enough light.

Water

Soil should be kept consistently moist both prior to and after germination. Before germination, using a spray bottle to gently mist the soil is recommended so as to not displace the seeds. Be careful not to overwater the lettuce seedlings - the soil should be moist but not waterlogged.

Temperature and Humidity

Lettuce thrives in room temperature conditions and should be cultivated in temperatures between 60F to 70F. Lettuce should not be exposed to warm drafts or cold winds, but instead kept at a relatively stable temperature.

Soil

Lettuce plants are not too fussy when it comes to soil, however, fresh soil should always be used. Reusing old soil won't provide the nutrients required for the lettuce to grow, and increases the possibility of introducing old bacteria and pests to the new plant. Seed starting mix (available at most nurseries and garden centers) is recommended if you are growing lettuce from seeds. If you are unable to find seed starting mix in stores you can easily make your own by mixing peat moss, vermiculite or perlite, and sand.

Fertilizer

Lettuce requires nitrogen-rich soil in order to thrive. As such, lettuce plants should be fertilized approximately three weeks after the seeds are planted, once the plant has established healthy leaves. When fertilizing the lettuce plant be sure to avoid the leaves of the lettuce to prevent leaf burn. Using organic, liquid-based fertilizer is recommended.

Propagating Lettuce

Lettuce is very easy to grow from seed and is generally ready to harvest a month after it is planted with germination occurring within a couple of weeks. To start lettuce from seeds, sow seeds approximately one inch apart in a seed starting mix and keep the soil consistently moist by misting daily until the seedlings sprout. Lettuce plants do not require deep growing containers as the root system is shallow, so seeds can be started in growing trays or recycled containers that can readily be found around the home - such as empty yogurt cups, egg cartons, or Tupperware containers.

Repotting

It usually isn’t necessary to repot lettuce plants if you are growing them from seed and the seeds are sowed properly (at least one inch apart). If you notice that the lettuce plants are looking crowded you can repot the plants into new containers to ensure they have enough space. Plastic containers work best for lettuce plants as they help to retain moisture, unlike clay or terracotta pots which tend to absorb water.

Varieties

There are five primary types of lettuce: leaf (loose-leaf), Cos or romaine, crisphead, butterhead, and stem (asparagus lettuce). Choosing the right lettuce variety to grow indoors is crucial to your success as some varieties adapt to indoor growing conditions more easily than others. Generally, loose-leaf varieties grow indoors more readily.
A couple of varieties that are especially suited to indoor growing include:

  • Black-seeded Simpson
  • Tom Thumb
  • Garden Babies
  • Merlot
  • Baby Oakleaf
  • Salad Bowl
  • Lolla Rosa
  • Red Deer Tongue

Arugula, Mesclun mixes, and baby spinach also tend to do well when grown indoors.

Harvesting Tips

After four to six weeks lettuce plants will be about four inches tall and should be ready to harvest. Try to harvest the lettuce in the morning as this is when the plant is the most hydrated and strong. Using sharp gardening shears or scissors, begin harvesting the lettuce from the outside and work inwards, snipping the lettuce leaves off just above the soil. Do not harvest the entire plant all at once, instead, clip three to four leaves at a time and leave the crown (or middle) of the lettuce plant intact to boost its overall harvesting yield. Since indoor lettuce plants grow and mature constantly, leaving the crown of the lettuce plant will allow the outside leaves to regrow and be harvested again. The lettuce should be ready to harvest again within two weeks.

Since lettuce is perishable, try to harvest only what you will immediately need. Lettuce leaves will only last between three to seven days in the fridge once they have been cut from the plant.