How to Grow Lettuce Indoors

Spring may be a great time for planting vegetables outdoors, but it's easy to grow lettuce indoors anytime of year. Similar to growing herbs indoors, all you need to do is provide the right indoor growing conditions and you’ll be on your way to harvesting fresh lettuce from the comfort of your own home. Whether you want to grow leaves that are bitter or mild, tender or crisp, some types of lettuce are better suited for growing indoors than others. Use this guide to find the best lettuces to grow indoors, along with simple steps to grow indoor lettuce any time of year. 

Best Types of Lettuce to Grow Indoors

• ‘Green Oak Leaf': The frilly, green leaves of this loose-leaf lettuce are very easy to grow and tend to have a mild flavor and crunch.
• ‘Red Oak Leaf’: This loose-leaf variety is great for spicing up salads with its dark red leaves and slightly bitter flavor.
• Baby Leaf Varieties such as ‘Red Sails,’ ‘Refugio,’ ‘Parris Island,’ and ‘Defender’ can be harvested at an early stage of growth.

Step-by-Step Guide for Growing Lettuce Indoors

1. Choose Your Indoor Growing Space

Find the sunniest spot in your home that provides at least six hours of bright sunlight a day. Choosing an area near a south-facing window usually provides the best amount of sunlight for growing lettuce indoors. Keep in mind that lettuce plants should not be placed in direct sunlight during the hottest part of a summer day, or they'll burn. If you don’t have enough natural light, invest in grow lights that are specifically designed for indoor gardening.

2. Modify Growing Conditions

Lettuce prefers cooler temperatures, so you’ll need to make sure the room that you’re germinating your seeds in has a temperature between 55°F and 65°F. Seedlings should be grown between 50°F to 60°F to keep them from bolting (trying to flower). Warm growing conditions could cause the plant to bolt early which makes the leaves taste unpleasantly bitter. It's also best to raise humidity levels around your plants because the air in your home is usually much drier than most outdoor environments. Help prevent diseases on your indoor lettuce plants by increasing air circulation with a small fan that will keep moist air moving gently around the plants.

3. Select a Suitable Container

Lettuce has a shallow root system, so it grows best in a medium-sized container. A container salad garden will do better in plastic than in terra cotta pots because the clay will dry out the soil mix faster than the plastic. An oblong-shaped container is great for a short row of lettuces. If your container has no drainage holes, make a few small holes in the base before planting.

4. Use a Potting Mix for Vegetables

Plant your lettuce seeds in fresh potting mix that is designated for vegetable growing. This mix will have the right drainage and little, if any, fertilizer. You can also mix your own potting soil from equal parts bagged and sterile compost, perlite, and coarse sand. Starting lettuce seeds in a fresh potting mix helps minimize diseases, pests, and weeds.

5. Buy Lettuce Seeds or Seedlings

Lettuce seed is available to buy throughout the year, or you can buy seedlings in cell packs from a garden center from spring to early summer. Remember to look for loose-leaf lettuce varieties because they are better suited to indoor growing than head lettuce types. 

6. Plant Lettuce Seeds at a Shallow Depth

Fill the pot with soil, so there’s about one inch of space between the top of the container and the soil. Sow your seeds on top of the soil, making sure they're spread out instead of clumped together. Lettuce seeds actually require light to sprout, so either leave them sitting on top of the soil, or very lightly cover the seeds with potting soil.

7. Water the Seeds with a Mist Bottle 

Use a mister bottle to spray the seeds with water on a daily basis so that the soil stays moist but not soaked. Watering the seeds directly with a watering can could cause the seeds to sink deeper into the soil or to wash to one side of the pot. Depending on the lettuce variety, you’ll start to see plants emerge in about one or two weeks.

8. Keep Lettuce Seedlings Well Watered

Once the plants emerge, continue to keep the soil moist but not soaked. Avoid overwatering by following the best practices for watering houseplants. Prevent root rot by removing any excess water that may collect under your pot.

9. Thin Out Weaker Seedlings

If several seedlings are sprouting close together, remove the weaker seedlings so that the stronger seedlings will have more room to expand to their full potential. Check the seed packet for your lettuce varieties' mature size and make sure you space them out accordingly.

10. Harvest Lettuce Anytime

Snip lettuce leaves when they’ve grown to the size you want. If you prefer smaller lettuce leaves, cut them when they’re about 6 inches long. Avoid cutting the inner leaves of each lettuce cluster to allow the immature growth to continue developing into larger leaves for future harvesting.