How to Grow Hydroponic Lettuce: Plant Care Tips

There’s a reason why lettuce is one of the most popular hydroponic crops for beginners and experts. The crisp, leafy green is easy to grow hydroponically, plus it's super versatile in the kitchen.

Lettuce is an extremely fast-growing hydroponic crop—it matures in about a month. You can easily germinate the seeds in a soilless growing medium before transferring them into a hydroponics system fitted only with a nutrient-rich solution.

The plant is a great source of minerals, fiber, and bioactive compounds—such as folate, B-carotene, and lutein—that promote a nutritious diet. Studies show that certain types of lettuces (those with darker or red pigments and leafy types) have anti-inflammatory, cholesterol-lowering, and anti-diabetic properties thanks to their bioactive compounds.

So, if you’re curious about starting your first hydroponics garden and need a beginner-friendly plant to kick it off, lettuce is what you're looking for. The following tips will get you going in the right direction. 

How to Plant Hydroponic Lettuce

Get started with hydroponic lettuce by germinating your seeds in a growing medium, such as rockwool, lightweight clay aggregate, coconut fiber, or perlite.

Growing From Seed

Don’t expect all your seeds to germinate properly—you'll likely have success with closer to 75% of them, depending on the type of lettuce. Fill your trays with a growing medium and slowly add water so the medium is moist but not soggy. Sprinkle up to three seeds in each plug and cover with about a quarter-inch of medium, compacting the seeds slightly. 

Continue to mist the seeds regularly to keep the growing medium moist as the plants develop. Once your lettuce has produced a few mature leaves and roots that stick out of the bottom of the medium (usually around two to three weeks or when they’re about two inches tall), it’s time to transplant the plants into your permanent hydroponics system. 

Transplanting

When transplanting your seedlings from the plug trays to the hydroponic system, it’s important to avoid pulling too hard at the new stalks since it can easily kill the plant. Gently, loosen the roots with your fingers and carefully place each seedling into its pot, tucking the roots through the slats so they dangle into the nutrient solution below.

Hydroponic Lettuce Care

Since hydroponic lettuce is extremely easy to grow, it doesn’t require much maintenance once established in your system.

Your plants' success will mostly come down to providing adequate light (which varies depending on whether you grow outdoors or indoors), maintaining air temperature, and adjusting the nutrient levels to ensure the best results.

Light

Lettuce doesn’t demand a lot of light, so start with 10 to 14 hours of moderate to low light each day. If plants don't get enough light, they won’t grow efficiently, while too much light may cause the leaves to go bitter.

Keep in mind that darker red leaf varieties won’t maintain their vibrant color under low light quality, so consider supplementary lighting if you notice your lettuce is a muted shade.

Water

Check your nutrient solution regularly for signs of evaporation and supplement accordingly (you’ll likely have to replace the entire solution every two to three weeks). After harvesting, you can use the spent solution to water your regular garden or house plants.

Temperature and Humidity

Remember to maintain a cool air temperature, preferably under 75 degrees Fahrenheit, as lettuce is a cool-season crop (hotter temperatures can cause your lettuce to grow bitter).

Keep day temperatures between 68 and 75 degrees Fahrenheit and night temperatures slightly lower, between 60 and 65 degrees Fahrenheit.

Growing Mediums and Nutrients

Since hydroponic lettuce grows with its roots directly in water, there’s no need for soil. Instead, gardeners use a growing medium to help the seedlings sprout initially and provide for the roots as the plant grows.

Stone wool (rockwool) and phenolic foam are common growing mediums for germinating lettuce, as are coconut fiber and perlite.

Leafy greens like lettuces require more nitrogen than other plants (nitrogen is best for providing nutrients and stimulating leaf growth). Lettuce also needs plenty of phosphorus to promote maturity and increase the harvest yield.

Hydroponic Lettuce Varieties

It’s possible to grow practically every type of lettuce hydroponically, though gardeners tend to lean towards loose-head varieties since it’s easier to harvest those leaves individually—thereby prolonging the entire plant’s harvest life. Some of the more popular types of hydroponically grown lettuce include the commonly grown butterhead lettuce, robust and crispy romaine lettuce, and varieties of mild loose-leaf lettuce.

Growing times for various types of lettuces vary as well. Butterhead and romaine, for example, are ready to harvest in about three to four weeks, while sturdier lettuces like iceberg are ready to eat in six to eight weeks.

How to Harvest Hydroponic Lettuce

Except for crisphead types (like iceberg lettuce), most lettuce varieties are best harvested by taking the bigger, outer individual leaves without removing the entire head. That way, the smaller, inner leaves have room to continue growing. That being said, you can also harvest the entire head at once, though it will take longer—anywhere from five to six weeks—to develop.

To harvest the whole head of lettuce at once, either remove the entire plant by cutting from the roots or cut off all of the leaves from the base of the plant.

If you plan on continuing your hydroponic lettuce garden, ensure you have replacement seedlings ready to replant into the system.

How to Store Hydroponic Lettuce

Eat individual lettuce leaves immediately. If you want to harvest your lettuce but won't be consuming it for a while, pick the entire head and store it in the refrigerator to keep it fresh for longer. To extend your lettuce's life even further, wrap the crown in a damp paper towel or place the bottom in a shallow bowl of water.