How to Grow Hydroponic Lettuce

People sometimes view hydroponics as complicated and expensive, but the truth is that it doesn’t have to be either one. It’s possible for you to grow an annual plant such as lettuce (Lactuca sativa) hydroponically in your back yard, on your deck or even in your home with very little investment or effort. You may be enjoying fresh lettuce in a matter of weeks after planting.

A raft system is one of the simplest hydroponic systems to set up and maintain, and it’s ideally suited for leaf lettuce (Lactuca sativa var. crispa). Choose the size of the system's reservoir -- the container that will hold a nutrient solution -- that fits your needs, but ensure the reservoir is at least 6 inches deep. Decide whether to place the system outdoors or indoors. If you opt for outdoors, then create a large hydroponic garden by making a 4-by-8-foot wooden frame that is 6 to 8 inches deep, and line its interior with a 6-millimeter-thick polyethylene plastic sheet, or use a plastic, kiddie wading pool. If your hydroponic system will be indoors, then using a storage tote or similar plastic container for the frame is more practical than using a large, wooden frame. Cut a piece of 1-inch-thick polystyrene foam -- the raft -- to float loosely on the nutrient solution that will be in the reservoir inside the frame, and cut round, 1-inch-diameter holes all the way through the foam, spacing them 6 inches apart over the foam's entire surface.

Place your hydroponics system in a location where its reservoir will get adequate light but won’t get too hot. Lettuce does best in temperatures that range from 60 to 70 degrees Fahrenheit; it also grows best during days that have no more than about 12 hours of daylight. Too much light or heat can cause lettuce to flower, and then it will not taste good. If you grow lettuce hydroponically indoors but don't have a sunny window, then hang a fluorescent light a few inches above your lettuce plants' tops, and add a timer to turn that artificial light on and off so the plants are exposed to the same amount of light every day.

Begin making the nutrient solution by combining 2 teaspoons of water-soluble, 20-20-20 fertilizer with 1 gallon of water. Ensure the fertilizer contains micronutrients because hydroponic plants can’t get them from soil. Then add 1 teaspoon of Epsom salts to the water-fertilizer mixture, and combine all the ingredients well, completing the nutrient solution. Fill the reservoir to a depth of at least 5 inches with the nutrient solution. Add more of the nutrient solution to the reservoir as needed to keep the solution at least 5 inches deep, but make fresh nutrient solution every time you need to add any to the reservoir because the solution doesn’t store well. Install an aquarium air pump near the reservoir, and insert an air stone in the reservoir to provide oxygen to the lettuce plants’ roots. Let the polystyrene foam float on the reservoir's nutrient solution; the floating foam is like a raft.

A hydroponic raft system can be used to grow many varieties of leaf lettuce. Some options include red or green leaf lettuce such as "Grand Rapids," "Oak Leaf," "Ruby" and "Red Fire." Soak one rock wool cube, available from hydroponics suppliers, for each hole in your system's polystyrene foam raft, and sprinkle a few lettuce seeds on the cubes. Insert the cubes so that each one fits snugly into its own hole in the polystyrene foam raft and just pokes through the foam's bottom. Water the cubes with plain water until the resulting lettuce plants grow enough for their roots to reach into the reservoir, watering themselves. As the plants first grow, remove excess ones as needed to avoid overcrowding; in general, keep only one plant in each cube. Harvest when the plants reach the desired size or stop growing, typically about four to six weeks after planting.