The Q&A Archives: Lighting

Question: I have a greenhouse, and have several types of lettuce, radish, spinach, garlic and chives seedlings. I am adding fluorescent lighting, and am wondering what would happen if I give the plants 24 hours of light. If that would be bad then what amount of total (including the natural sunlight that they get in the greenhouse this time of year) would be optimal?

Answer: It's easy to think that exposure to light 24 hours a day should result in faster growing, larger vegetables, but the truth is that it won't. Plants need a rest period to recover from the day's work and to store energy in preparation for the next day. You can keep the lights on 14-16 hours each day, which will replicate the long days of summer, but you need to turn them out at night. If you leave the lights on longer, the plants will grow weak and spindly rather than stout and healthy, which will defeat the purpose of growing your own fresh and healthful veggies.

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