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Growing Lettuce Indoors For Salad Success

Growing lettuce indoors is a great way to garden from the comfort of your own home. Whether you want to grow a head of lettuce or one of those loose-leaf varieties, these plants are a great way to try your hand at indoor gardening. And you’ll have a salad bowl full of fresh greens when you’re done. 

You can grow lettuce in potting soil in a pot indoors rather than in your garden. With so many lettuce varieties you have tons of plants to choose from. Try head lettuce, like Romaine or Tom Thumb. Or try microgreens from seed and cut them for salads and sandwiches when they are ready to harvest. 

Grow lettuce indoors in a hydroponic garden, in a pot or container, or in a grow tent. Keep your plants strong and have lettuce year-round. From seed to seed starting, to harvest, lettuce is a lot of fun to cultivate. And it’s healthy. If you have lettuce to grow, then there’s no excuse not to incorporate this crunch in your meals! 

Ways Of Growing Lettuce Indoors

Growing lettuce indoors
Growing lettuce indoors is not only possible, it can be really rewarding. Source: bezajel

Grow lettuce indoors in a sunny window. Bay windows are even better for growing lettuce. If you don’t have a window with extended amounts of sunlight per day, another method in this section is better. 

Lettuce plants have shallow roots, making them one of the easiest candidates for container growing. Both heading lettuces and loose-leaf varieties can be successfully grown in a window as long as there aren’t obstructions that will block out sunlight. This makes it possible to plant lettuce in a pot and grow it all year long — even in the winter when tender leaves would be damaged. 

If a window is not an option for you, grow lettuce or lettuce microgreens under grow lights. Because lettuce doesn’t like hard direct light, LED grow lights work. With advances in technology, there are tons of LED options. Pick up a grid LED for both heading and loose-leaf lettuces. Don’t have a grow light? No problem! A shop light also works.  

Growing lettuce under lights gives you leaf lettuce and crunch that you crave all year round. If you have enough space for a lettuce plant, this is a great option. However, if you don’t have room to host plants, lights, and trays to hold everything, try one of the other methods listed below.

Grow tents are excellent for people with enough space. Smaller grow tents sit on a countertop, and take up about 18 inches of space. Larger tents sit on the floor in a corner and take up about two by four feet of space. Because lettuce won’t require a lot of depth to grow, and it won’t get very tall, a small grow tent is suitable. 

Grow tents give both leaf and heading lettuces environmental controls that growers can’t get elsewhere. Temperature, humidity, light, and water are all easily maintained. But if you’re interested in growing a lot more than just a few lettuce plants, grow tents aren’t the best option. To grow lettuce indoors on a mass scale, try hydroponics. 

Hydroponics can be a great choice for growing indoors. Depending on the variety, try a stackable system that sits on a countertop or even one on a rack. These systems contain everything an indoor grower needs: lights, containers, and racks. However, they can be expensive. Instead of feeding plants with decayed matter like potting soil, hydroponics requires solutions to feed lettuce sprouts. Nutrient solutions cost money. 

Still, lettuces thrive in a fully functioning hydroponic system. Depending on the variety, you should be able to grow lots of fresh lettuce in this manner. Keep in mind, though, that any breakdown in the hydroponic system could devastate your crop. Keep an eye on your plants daily. 

Caring For Indoor Lettuce

Lettuce is a happy plant that is easy to grow as long as conditions are right. If you provide proper amounts of sunshine, water, and nutrients lettuce needs, you’ll grow a lovely salad mix in 7 to 9 weeks. 

Lighting & Temperature

Young leaf lettuce
Leaf lettuces are also an excellent choice for indoor growing. Source: metaphoricalplatypus

Lettuce appreciates at least 12 hours of full to partial sun per day outdoors. Indoors, how many hours of light you provide is dependent on the type of radiation given. Those growing lettuce in a window (north or south-facing depending on the hemisphere) should place pots where there is at least that same amount. 

Indoor lettuce under grow lights has varying needs depending on the setup, too. Lower wattage is best for these tender greens. Loose-leaf lettuce and heading lettuce appreciates shade outdoors, so don’t put a grow light close to the plant.

To begin starting seeds, give them at least 14 to 16 hours of light. Lettuce seeds need soil temperatures of 70 to 75 degrees, which is about the temperature of most homes where indoor growing takes place. Once your seed starting process is complete, move lettuce seedlings to an area that has 12 hours of light. 

If you place your lettuce plants or seedlings in direct proximity to an air conditioning vent, this could negatively impact growth. Air outflow dries out soil or creates conditions too cold for seed germination. Keep your station away from HVAC systems if at all possible. If it’s not possible, monitor your containers to ensure conditions are right for seeds or lettuce growing there.

Water & Humidity

The most important part of lettuce growing indoors is ample water. Use a spray bottle in non-hydroponic setups. Keep the soil moist, but not too wet. Prevent dryness in the soil where lettuce grows. 

Check the top inch of soil to determine whether or not it’s time to water again. The location of your containers will affect how to water. Windows with sunlight and lights dry out soil more quickly than those in a grow tent or hydroponic system. Wicking mats are one way to keep lettuce well-watered. 

Humidity should be at about 50 to 70 percent. Higher humidity can cause fungus development in your containers or on the lettuce leaves and head.

Spray bottles are the best way to water indoor seedlings, loose-leaf lettuce, and heading lettuce. This ensures the soil is moist enough but doesn’t leave the container in a puddle of water. But if the soil is really dry, don’t hesitate to give your plants’ soil a good soaking. Just be sure the excess moisture drains away without pooling under the pot.

In hydroponics, humidity is ambient. Change the water in a hydroponic system every two to three weeks. 

Growing Medium & Container

Soilless growing mixes work well for starting lettuce seeds. Use a combination of peat moss or coconut coir, vermiculite, and sand to prep your starting site. When lettuce seedlings get large enough, plant them into a mix of potting soil and sand and space them apart, or keep growing lettuce in a soilless mix with added fertilizer. The key to healthy lettuce you grow indoors is good drainage. Some types of lettuce will need richer media to thrive as they mature. For example, butterhead gets its flavor from nutrients in the soil. 

Containers don’t have to be deep since lettuce roots are relatively shallow. Some guides recommend plastic wicking trays to give lettuce the water it needs. But the container you choose is highly dependent upon location. If you’re using a full hydroponic setup, containers are provided. 

Terracotta pots heat up and dry out the planting medium quickly when under grow lights or in direct sun. Plastic containers are best. They hold moisture and don’t dry out easily. A self-watering pot doesn’t work for many indoor growing situations, but lettuce appreciates extra access to moisture.

Fertilizing

Since lettuce enjoys high amounts of water, you’ll need to replace nutrients that flow through the soil as it consumes water. Growing lettuce indoors involves applying fertilizer at planting time and a couple of times in the growing process. Hydroponically grown lettuce needs nutrient solutions replaced every few weeks. 

Add a full spectrum fertilizer in other indoor growing situations after each time you harvest your lettuce plant’s outer leaves. To harvest a full head of lettuce, apply a 10-10-10 or 5-5-5 dry or liquid fertilizer diluted to half-strength every two weeks. Avoid applying fertilizer to tender leaves which burn in contact with concentrated nutrients. 

Pruning

Lettuce in pot
Some varieties, like romaine, can do really well inside. Source: Mandie

To grow lettuce indoors, you’ll need to know how to harvest lettuce properly. Thankfully, you don’t have to fuss with this too much because lettuce is ready to harvest at almost any stage! 

To harvest baby greens sown close together, prune them by cutting them down about an inch above the medium. Make sure you have enough growth that you don’t prevent future harvests. You can prune outer leaves of heading lettuces, like romaine for instance, and use them as needed. The rest of the lettuce grows on even without outer leaves. To harvest a whole head of lettuce, take a sharp knife and cut the base. 

If you’re growing lettuce that contracts a disease, trim off damaged leaves as necessary. They will grow back. 

When lettuce gets too hot, it bolts. Remove flower stems quickly to keep growing lettuce indoors instead of allowing the plant to divert nutrients to flower production. However, if you’d like to collect lettuce seeds it’s perfectly ok to let them flower, then collect seeds. For the best fresh lettuce, you’ll want to carry out harvesting before bolting occurs as the leaves may turn bitter during flowering. 

Planting

Sow lettuce seeds one inch apart in a shallow container to start them. As they grow into a lettuce plant, transplant them in a pot, container, or hydroponic set up individually or up to six inches apart. Sow microgreen seeds closer together in their tray as they can be densely planted.

Hydroponically grown lettuce seeds start well in coir pellets. Sow a few seeds per pod. Thin the sprouts to the strongest seedlings. Transfer them into net pots in your setup when roots start to emerge from the medium. 

When growing lettuce indoors, don’t plant head lettuce close together. Planting lettuce seeds that will form heads close together prevents proper nutrient uptake. Instead, provide ample room between each heading lettuce. This could be one pot per plant or a location with at least six inches of room between plants. Taller lettuces, like Romaine, may be able to tolerate slightly more crowded conditions in your indoor garden than other heading lettuce.

Troubleshooting

Common indoor lettuce problems stem from improper conditions. Keep in mind, good drainage is key. Proper sunlight (or synthetic sources) will give you lush, crunchy leaves when harvesting comes. If there is an imbalance in one of these areas, you’ll know. 

Lettuce is a cool-weather crop that will bolt in high heat. Decrease heat sources to prevent bolting. Use lower wattage grow bulbs. If you’re working in a windowsill garden, move lettuce out of direct sunlight before it bolts, or provide afternoon shade. If heat and brightness aren’t a problem, harvesting at improper times can give lettuce the idea it’s time to bolt. Bolted lettuce has a bitter flavor due to the shift of nutrients to flower production instead of leaf production. 

Roots that are in oversaturated soil for too long may rot, causing wilting, yellowing, or damage to the lettuce plant. Dry soil may also cause leaf wilt. Remember to keep the soil moist, but don’t soak it. Check daily to ensure the water content is right. 

Wet media attracts fungus gnats, which aren’t a problem at first. Gnats feed on lettuce leaves when there are enough of them, though. Apple cider vinegar traps contain fungus gnats.

Lettuce that lacks nutrients will halt growth. Provide nutrients in the medium and via fertilizer to prevent this.

If you’ve ever seen streaks of red on your romaine lettuce and wondered what was going on, know this is due to the age of your plant. Older plants are prone to oxidation that causes discoloration and flavor changes. Harvest oxidized lettuce immediately and eat it. 

Lettuce plants without enough space that are competing for nutrients with each other won’t form heads. Try moving heads into containers with more space between them to remediate this issue.