How to Grow Lettuce Indoors

Lettuce grows quickly from seed. Plant 2 sites in a 6″ / 1-quart container. In larger containers, space sites 3″ apart. For each site press 2 seeds into the surface. Keep the soil warm ( 40-80°F, ideally 70°F). Sprouts typically appear in 7 days but can be as quick as 2 days or as long as 10 days depending on your conditions. 

How to Transplant Lettuce

Live starter plants give you a little jump start on your first harvest. When you’re in a garden center – pick the bushiest plant available (tall and lanky ones will be weak growers) and give it a good inspection for pests. Leaves should be dark green without holes, spots, or curled edges. A best practice is to actually “quarantine” your plant for about a week after bringing it home to make sure it’s free and clear of ride-on pests. 

1. Remove some soil from its final planter – leaving enough space for the bottom of the seedling to be just higher than the soil surface.
2. Hold on to the base of the stem with one hand, and turn the pot over while gently pulling the seedling. Giving the pot a few squeezes can help dislodge it.  
3. Place in its final container and fill around it with soil so that it’s tight, but not compacted.  

Where to grow your Lettuce plants

Out of all edible plants, Lettuce plants have some of the lowest light needs – but they still need to be in a very bright place that gets at least 4+ hours of direct sunshine. While you might be lucky enough to have a bright windowsill that works, most of us need to use a grow light (especially during the winter). For an introduction to grow lights, head over to our post on grow lights for indoor gardeners. We’ve also got a buying guide for screw in types, but to keep things simple in this guide, we’ll just provide directions for the 24W Screw in Bulb by Sansi, which we think is a good middle-of-the-road option.

How bright should your grow light be? 

Lettuce plants need the equivalent of 4+ hours of direct sunlight [DLI of 12+ mol/m²/day] to grow their best. In order to provide an equivalent amount with a grow light, it needs to be pretty bright! The 24W Sansi bulb should be placed 6 inches away from the top of the plant. This will give your PPFD (the standard measure of brightness) of 500 μmol/m²/s.

How many hours per day do your Lettuce plants need under a grow light?

Lettuce plants are known as “long-day”. When they sense over 12 hours of light per day, they’ll start the end of their lifecycle and work on making seeds.  We want to keep them in an earlier stage so we can keep harvesting the leaves, so we recommend setting up a timer to leave it on for only 8 hours per day.

Extend your harvest by keeping the Temperatures Cool 

Lettuce is known as a “cool weather crop.” If it senses warming temperatures it will “bolt” –  send up flowers and become bitter in the process. Where you plant them can have some effect on the temperature – lower positions on a growing rack, ceramic planters, and hydroponics with air bubblers tend to run cooler. It’s best to avoid windows that get really hot (like bay windows)

Week 1-2: Check for Sprouts

You could see seedlings in as little as 2 days (though 7 days is more typical). If it’s been 10 days and you still don’t have any sprouts, it’s likely that your setup is too cold.

Week 3: Check Your Seedlings

There’s no need to thin Lettuce, but you should check on your seedlings’ progress to make sure you’ve got enough light. They should be about 1 inch tall by the end of Week 3. If they aren’t you likely need a bit more light.

Week 5: How to Prune Lettuce

You’ll notice how all the stems and leaves of Lettuce grow from a single, central point (called radial growth). The plant puts out new leaves in the center and pushes old leaves outward, getting bigger and bushier over time. Pruning and harvesting are one-in-the-same with Lettuce. Once the plant at least 3 separate stems coming from the base take one of the outside leaves and cut it close to the base (½” above is fine). It’s good to leave at least 2/3rds of the plant left to regrow.

Month 2+: How to Harvest Lettuce

Just the lettuce at the base of the plant. 

Month 4: End of Life

Leaf lettuce is best harvested as the entire plant – so once you harvest it’s time to start over. 

Shop This Blog

The right supplies can take the guesswork out of caring for your plants – and turn care from a daily to weekly routine. Through our grow tests, we’ve found these products to produce the best indoor Lettuce (and also have simple maintenance).  Plants are adaptable and can grow in many different conditions, so they are by no means necessary if you already have other supplies.

Best Containers for Lettuce: Ceramic Self Watering Planters

Plants thrive on consistent moisture but can suffer if they’re waterlogged. A semi-porous ceramic self regulates ideal conditions. Our favorite is the COSWIP planter. Runner up is XS Self Watering Planter by Wet Pot.

Best Soil for Lettuce: Standard Potting Mix

Lettuce likes a rich and moist root zone – so you are best off with a standard potting mix – we like this Organic Mix by Espoma. 

Best Nutrients for Lettuce: Balanced Blend

Lettuce likes nutrients that are equal parts nitrogen, phosphorus, and potassium (with NPK numbers like 10-10-10). For a Balanced Blend we recommend: Dr Earth All Purpose

Best Light for Lettuce: DIY or Soltech

There is a very small chance that you have the bright windows needed to grow these without a grow light. If you are looking for a higher-end option – we love the Aspect Light by Soltech. For a more affordable option, a DIY setup using a 24W Screw-in Bulb by Sansi with a Clamp Light and Mechanical Timer works well too.  Check out our complete guide on a DIY setup for less than $40 or our buying guide for screw in bulbs.