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Planting Hydroponic Lettuce

Hydroponic lettuce at four weeks and one week.

Greetings from western Pennsylvania! I have been learning hydroponics throughout my summer internship at Yarnick’s Farm. I have found great interest and opportunity learning about the entire system from seedling to sale.


Green and Red Bibb lettuce, kale and Red Oakleaf lettuce are all grown hydroponically in the greenhouses. Plants grown without soil are considered to be hydroponically grown. Confusing as it may be, hydroponics encompasses plants grown in foam, gel, perlite, or water. On Yarnick’s farm, the lettuce is grown hydroponically in foam and water.


The process begins with a foam tray. One lettuce seed is placed in each hole in the foam tray. This tray is then watered as any normal sprouting seedling would be. The sprouting seeds must be kept in moist conditions. The trays must constantly be monitored; a dried tray equals a loss of seeds, foam, money and most importantly, time.


After the first two true leaves erupt from the young seedling, each foam square containing this delicate seedling can be planted. Due to timing issues, the plants may have two true leaves or five beautifully developed, upright leaves. The foam squares are carefully separated. If the seedlings are damaged, have abnormal growth (sideways) or look inferior (yellow leaves, small, signs of oxidation), they are discarded or left to grow a little longer.

Planting Red Bibb lettuce in the hydroponic channels.


Each foam square will be planted into one channel. The foam is slightly smaller than the square hole and must be level. If the foam is slightly tilted, the plant will grow in a tilted manner. This disrupts the uniformity that the greenhouse gives a grower. It also interferes with the surrounding plant’s growth habits, causing greater uniformity problems. To many consumers, an abnormal looking plant is unappetizing, even if its nutritional value is not affected.


A fertilizer is mixed into the water that is pumped throughout the system. A filter will capture roots, dirt, bugs or unwanted items that can plug the entire system. The lettuce must routinely checked to make sure it’s nutritional and environmental needs are met. If the system was to get plugged or turned off for any reason, the plants will immediately begin wilting, dying and crop loss will become inevitable.


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