GROW LETTUCE INDOORS
Before you start growing indoors, learn the basics about type, temperature, and light.
If the basics are doable for you, then follow the step-by-step directions that are further down the page.
Lots of varieties can grow indoors and can be picked whenever to meet space needs. However, there are a few that are more popular for indoors.
Most lettuce varieties can survive basement temps or even beside a cooler window. Optimal growth happens between 60 and 70°F.
Lettuce isn't as light hungry as many other vegetables. You can grow well in most sunny south or west-facing windows or use grow lights.
Step #1 Prep
Nearly any seed will do! Get your seeds from a local garden shop, farmer, or trusted seed company. Common indoor favorites include Baby Oakleaf, Black-Seeded Simpson, Garden Babies, Lollo Rosa, Merlot, Red Deer Tongue, Salad Bowl, Tom Thumb.
You can also grow lettuce from the stem/heart of an existing head. The stem is just the butt end that you cut off or break the leaves off from before eating. Romaine is the easiest for this. Learn more about this method in step #2.
Transplanting lettuce can be annoying, so just sow where you'll grow. Using "Indoor Potting Soil/Mix" to both germinate and grow your lettuce is more efficient and just as effective. You can also reuse indoor potting soil that's healthy and that was previously used to grow other edible plants (it will just need fertilizer boosts). It's important to purchase an indoor-specific soil from a place that has kept the soil indoors as well. Indoor storage reduces the chance of bringing in unwanted house guests (aka bugs).
Lettuce has a shallow root system, but is always thirsty. The smaller and more shallow your container, the more frequent you may need to water. With that said, pick whatever container you want and experiment. Most window sill planters work great for lettuce.
As a loose rule, you'll only keep 1 plant in a 4-6" pot, 2-3 plants in a 8-10" pot and 3-4 plants in a 10-12" pot. You can always harvest a full plant out of a pot if it's too busy with lettuce.
No matter what size container you choose, make sure it has drainage holes and you have a plate/saucer beneath it.
You may also need fertilizer, a grow light, spray bottle, watering can, and a sharp scissors.
Step #2 Plant
Fill 3/4 of your pot with moistened soil. Sprinkle several seeds in your pot, perhaps twice the amount of seeds you actually want (e.g., if you want 1 lettuce plant, sow 2 seeds). Lettuce seeds are tiny, so this may be difficult. Don't worry! You'll later thin out (and eat!) any extra plants that might crowd your pot.
There's no need to cover the seeds. Most lettuce varieties germinate better with light and temps between 60 and 70°F, so place the pot wherever you plan to grow your lettuce.
Optional Step: Cover your container with a see-through glass or plastic cover/wrap at this point to create a warmer and more humid environment for your seeds. This may speed up germination and reduce the need to mist the soil with water (Step #3).
Romaine lettuce is the most successful variety to grow from a cutting. Just cut all the leaves off the stem end, to create a 1" tall (or so) stem and leaf cutting.
Fill a bowl/container with abou 1/2" of water and place the stem in with the cut end facing up. Any container/bowl that can hold a few inches of water works well.
Place the jar next to your best growing window or under your grow light (see step #6). Change out the water daily (don't forget- stagnant water breeds bad bugs). You can harvest the leaves in about 2 weeks. Harvests may start to dwindle unless you start using a bit of hydroponic-friendly fertilizer for future heads or bury it in dirt (see option below).
Option: After you see some leaves appearing, you can move your lettuce to soil.
Just fill a container 3/4 full of moistened soil. Dig a hole big enough to plant the stem and deep enough that only the very bottoms of the newly growing leaves are popping out of the soil. You can now head to step #5.
Step #3 Mist
Your fragile seeds don't want to be knocked around when they're trying to grow. To avoid disturbing them, use a spray bottle to mist them with water.
Mist them daily to keep the soil moist. You may need to mist in the morning and night if the soil seems dry. Remember, if you have a cover on your seeds, you may not need to water much.
Don't have a spray bottle? Dribble water on the soil close to your seeds by dipping your fingers in a cup of water and shaking off the water over your pot.
Step #4 Wait
Lettuce seeds are fairly quick to germinate, usually 3-5 days.
Once your little plants erupt, remove any clear covering you may have had on them.
Troubleshoot: If no leaves appear after 10 days, consider starting a new pot. Check the dates of your seeds and soil to make sure they're still healthy. Consider putting your next pot of seeds on top of the fridge for some extra warmth (just don't forget they're up there!).
Step #5 Water
Lettuce likes well-drained soil that is moist, but never soggy. There are two common methods for indoor watering: Top watering and bottom watering.
Top watering is the usual watering method. You'll simply water the soil near the main stem of the plant. Use a watering can that has small holes or continue to mist until your plant can handle the pour of a bigger watering can or jar.
Bottom watering just means placing water in the saucer/drip pan under the pot (rather than watering the soil from the top). The roots suck up the water through the soil. Some growers do this from the very beginning.
Bottom watering can help deter insects and help the plant grow even more stable and strong. That's a really good thing for top-heavy plants (like tomatoes or peppers). If bottom watering, it's also helpful to flush the plant monthly by top watering to soak. Dump out any water that flows into the saucer. Not sure about watering from the bottom quite yet? No worries! Water from the top.
Step #6 Light
Now it's time to feed your plants the light they need to grow.
South or West-Facing Window
Lettuce can grow well next to a non-drafty window that gets at least 8 hours of sun. Rotate your plant every few days for even exposure. You'll know if your window isn't doing the job. Your lettuce will get tall and weak, looking frail rather than full. If that happens, try a different window or a grow light.
- Standard Fluorescent: Keep this light about 2 inches from the top of your lettuce and keep on lettuce for 14-18 hours.
- Compact Fluorescent: Keep about 1 foot from the top of your lettuce and keep on for 12-16 hours.
- LED: Keep about 1-2 feet from top of lettuce and keep on for 8-16 hours.
Rotate your plant every couple of days or so to get even light exposure. Your plants will also tell you if the lights are too close or too far away:
- Too close: Leaves will get burned and look brown/yellow.
- Too far: Tall, weak-looking plants that are growing slow.
Step #7 Thin
Thinning lettuce is more of a progressive thinning/eating process. If you have more than one seedling in your pot:
- If there are two plants super|close together, then pull one to avoid a tangled mess later that you can't undo.
- If you like, move a few of the plants to space them out in the pot (gently!) or into other pots.
- You can also just leave as many plants as you have that aren't on top of each other and let them grow a bit. You can then harvest one or more of the young lettuce plant(s) when you feel the pot is getting crowded. You'll then make space for the chosen plant(s) to get bigger.
Step #8 Prune
You don't need to prune lettuce. However, if your lettuce starts to bolt, then you need to harvest the full plant (or wait and collect the seeds to plant again).
Bolting means that the seed stalk is now taking over and leaves will stop growing and will taste bitter. It's not worth trying to save the plant at this point.
Step #9 Fertilize
Lettuce grows so fast that it doesn't need much fertilizer. If your soil is new, check the bag as some soil mixes provide enough nutrients for several months and you won't need to fertilize at all.
If your soil needs a boost, then fertilize as early as 2-3 weeks after germination. Signs of needing fertilizer include dull colored leaves and flavor and noticeably stunted growth.
Just a 1/2 dose of an organic fertilizer is usually enough (I like seaweed based fertilizers). An organic, plant-based fertilizer is generally simple to use and is more forgiving of mistakes. Start with less and build up as needed.
Step #10 Harvest
If you have a leaf variety, you can harvest outer leaves in as soon as 2 weeks after germination. These still may be small, but these early leaves are delicious. You can continue to harvest leaves for as long as your plant offers. These leaf varieties are cut-and-come-again, meaning they continually produce leaves to replenish the ones harvested.
If you do a heavy harvest and only leave 1/3 of the plant remaining, then give your lettuce at least 1 week to heal up before harvesting again.
Romaine, iceberg, or other "head" varieties take longer. Refer to your seed pack for direction on when to harvest your particular variety. However, most heads take about 10 weeks if you want the full head.
Some of these head varieties can also be harvested leaf by leaf much earlier than 10 weeks. Simply cut each leaf off near the base.