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How to Use Grow Lights to Start Seeds

By Marie Mulrooney ; Updated September 21, 2017

Grow lights can give you a jump on the growing season by enabling you to start plants from seed inside. Select a grow light that provides an abundance of blue and red lighting; the blue end of the spectrum is most important. If you’re willing to shell out a lot of money, metal halide high intensity discharge (HID) grow lights are the most efficient and effective. You can also use inexpensive fluorescent shop lights labeled as “cool” or “cool white” to good effect. While some seeds may have special needs in order to sprout, most will flourish if you follow a few simple steps.

Plant your seeds in containers about as deep as the seeds are long. Moisten the soil and cover it with plastic, if appropriate, to maintain humidity and heat.

Place the seed containers under your grow light fixture. If you’re using a shop light or other conventional fluorescent light, adjust it to hang between 2 and 4 inches about the soil's surface. HID lights should hang between 2 and 6 feet from the soil's surface, depending on their strength (the stronger the lighting, the higher it should hang).

Use a light timer, available from any home improvement or lighting store, to keep your grow light on a cycle of 16 hours of light and 8 hours of darkness to simulate spring light conditions.

Maintain your seeds by keeping the soil moist, but not soggy, and check every day for signs of growth.

Adjust your grow lights upward to allow for plant growth as seedlings emerge. If the seedlings look leggy or spindly, the light is too far away; if the leaves curl down and under, the light is too close.

Transplant the seedlings to their permanent location as soon as they’ve reached the desired size, or as conditions permit.

 

Things You Will Need

  • Light timer

Tips

  • Always label your seed containers, along with the date planted, so you can monitor your seedlings' progress.
  • Replace conventional fluorescent lighting tubes every six months, and more expensive grow lighting about every two years, to ensure the brightest possible light. The decrease in lumens is not visible to the naked eye, but your plants will notice.