How to Grow Lettuce Under Lights
- 1). Fill a seedling tray with a soilless potting mixture. Water the potting mix until it is evenly moist throughout.
- 2). Sow the lettuce seeds on the soil surface, spacing the seeds 2 inches apart in rows that are also spaced 2 inches apart. Cover the seeds with a 1/8-inch layer of potting mix.
- 3). Slide the tray into a clear plastic bag. Set it in a 65 to 75 degree Fahrenheit location to germinate, which takes approximately seven days. Lettuce doesn't require light for germination.
- 4). Remove the plastic bag once the sprouts emerge from the potting mix. Set the tray under a fluorescent grow light, adjust the light so it sits 6 inches above the top of the plants. Leave the lights on for 14 to 16 hours a day.
- 5). Water the lettuce when the soil surface dries. Provide just enough water to moisten the potting mix without making it soggy.
- 6). Thin the plants once they are 4 inches tall. Pluck out the excess plants so the remaining ones are spaced 4 to 5 inches apart in all directions.
- 7). Adjust the height of the light fixture as the lettuce grows, maintaining the 6-inch distance between the plants and the light.
- 8). Fertilize the lettuce every two weeks with a balanced, soluble fertilizer applied at half the rate recommended on the package. Begin fertilization two weeks after the seeds germinate.
- 9). Harvest the lettuce once the plants have at least six leaves. Remove the outer leaves for use while leaving the interior leaves as those at the top of the stem in place to continue growing.
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