How Long Do Tomatoes Need to Be Under Grow Lights?


All plants require light in order to perform photosynthesis. Tomato plants require a large amount of light for the majority of each day. Grow lights provide consistent and dependable light to tomato plants regardless of weather since the plants and lights are kept indoors. Up to 30 plants can utilize one full size grow lamp, or other plants can be grown alongside a smaller number of tomato plants.

Time Span

Leave the lights on for most of the day. Tomato plants outside can survive on six to 10 hours of sunlight. recommends 12 to 16 hours of light a day under grow lights to maximize the number of tomatoes for harvesting. Healthy tomato plants under grow lights are capable of producing fruit in as little as four to five hours under consistent light. According to the Web site Planet Natural, tomato plans take 90 to 140 days from seed to mature plant. Transplanted plants or those that are already past the seed stage will begin producing fruit within 60-90 days. During the growth period until the end of fruit production, plants need to be under grow lights for the majority of each day. Fruit production periods can last a few weeks to a few months depending on the health of the plant.


Install lamps in an area where the distance between the tops of the plants and the lights is two to three inches. The plant's shelf or the lamp fixture should be movable to adjust as the plants get taller. Having the plants closer than two inches from the surface of the lamp can cause a fire hazard as well as damage the plants. A 48-inch long fluorescent light fixture with GE Aquarium and Plant tubes is recommended by GrowYourTomatoes. Connect the lights to a light timer and set the timer to keep the lights on for 12-16 hours a day. For example, set the timer to turn on at 6 a.m. and turn off at 8 p.m. Do not leave them on all the time.

Keywords: grow light setup, photosynthesis by lamp, indoor vegetable gardens, tomato sunlight requirements, producing plants

About this Author

Maxwell Payne has been a freelance writer since 2007. His work has appeared in various print and online publications. He holds a Bachelor of Science in integrated science, business and technology.

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