How to Use Grow Lights for Seed Starting

closeup of tomato seedlings in plastic tray with soil under purple LED grow light


Project Overview
  • Working Time: 30 mins - 1 hr
  • Total Time: 30 mins - 1 hr
  • Skill Level: Intermediate
  • Estimated Cost: $12 to $200+

Growing your own plants from seed is a great way to garden on a budget, but even the sunniest south-facing window typically isn't bright enough for indoor seed starting. You can cultivate strong, healthy vegetable, herb, and flower seedlings indoors by using grow lights.

Without enough light, your seedlings will grow long and leggy as they attempt to reach the light source, producing skinny, weak stems. Plants raised under a grow light as seedlings grow stronger and more vigorous than those that were grown without. Grow lights shine down from above, encouraging seedlings to grow straight up, rather than bending over toward the light from a window. Here's what you need to know to start seeds using grow lights.

Why Use Grow Lights for Seed Starting?

Plants require certain wavelengths of light to photosynthesize, specifically those in the red and blue portions of the light spectrum, which regular white lights don't emit. Grow lights should be full-spectrum, meaning they put out similar wavelengths of light as those emitted by the sun, or emit blue and red wavelengths specifically. Full-spectrum grow lights provide the same colors that mimic daylight, perfect for starting your plants.

Grow lights come in a variety of sizes, types, and styles. They can be LED bulbs that fit into a standard fixture, LED panels that hang from the ceiling, or fluorescent tube lights mounted in a rack specifically designed for seed starting. Incandescent grow lights are available but less energy-efficient than LED grow lights or fluorescent bulbs.

When to Use Grow Lights for Seed Starting

When to start seeds using grow lights depends on the types of seeds you're planting. Seeds are often started in late winter and early spring, anywhere from four to eight weeks before the last frost date in your USDA plant hardiness zone. Some plants, like perennials, may need even longer. Check seed packets for information on when to start seeds indoors in relation to your region's last frost date.

Many plants don't need light until they've sprouted, so you'll start using grow lights once your seeds begin to germinate and the first leaves poke through the soil. However, some seeds must be sown on the surface and receive bright light to germinate in the first place, so be sure to check the directions on your seed packet.

Before Getting Started

As you shop for grow lights, consider your budget and how much space you have to devote to seed starting. If you have a small space and are only starting one or two trays of seeds, an LED grow light bulb may be enough. This kind of lighting setup only costs around $12, not counting a fixture to hold the bulbs.

If you want to start several trays of seeds and have the space, you can purchase a ready-made seed starting rack fitted with lights for $200 or more, or purchase the lights alone and turn a bookshelf or wire rack into a seed starting shelf. It's also important to note that fluorescent lights tend to be cheaper upfront but burn out more quickly, while LEDs may cost more to purchase but are more energy efficient.

Grow lights should be positioned close to the seedlings to avoid them stretching to the light and becoming leggy and weak. An adjustable light source that can be raised as the plants grow makes a perfect addition to your seed starting station. This can be as simple as inexpensive shop lights with full-spectrum bulbs, hung on chains that can be raised as the plants grow. Position the lights 2-3 inches above the seedlings, and move the lights up as the plants grow, keeping them always close--but not touching--the seedlings.

Note that seedlings need 14 to 16 hours of light per day. You can turn grow lights on and off manually each morning and evening, but an outlet timer is much more convenient and will ensure that your lights turn on and off at the same time each day. Make sure that your plants also have at least 8 hours of dark each day as well.

What You'll Need

Equipment / Tools

  • Grow light
  • Adjustable chains for light
  • Outlet timer
  • Pen or marker
  • Spray bottle for water


  • Seeds
  • Seed trays or containers
  • Seed starting mix
  • Plastic bags or tray covers
  • Labels


How to Use Grow Lights for Seed Starting

  1. Choose a Site for Seed Starting

    Before planting seeds, consider where and how you'll set up your grow lights and seed trays. If you're using bulbs, you'll need something to screw them into so they'll shine above your seed trays. Fluorescent grow light fixtures will need to be mounted or hung above seed trays. A seed starting rack can be kept in a spare room or empty closet.

  2. Install Grow Lights and Outlet Timer

    Follow manufacturer instructions to set up or install your grow lights at an appropriate distance from where your seed trays will be. Check to ensure they're operational before sowing your seeds. Plug your lights into an outlet timer so they'll turn on and off automatically when the time comes. Consider using adjustable chains to raise and lower your grow lights.


    Adjust the distance between your seedlings and a basic grow light by stacking books or boxes beneath your seed trays as the plants mature. Make sure to protect books from water and soil.

  3. Sow Seeds

    Moisten your growing medium, fill your seed trays, and sow seeds according to the directions on the packet. Label your seedlings so you know what's planted where. Cover seed trays with clear plastic lids or tent clear plastic over the trays to keep them from drying out. If the seeds you're planting require light to germinate, skip to step 5.

  4. Watch for Sprouts

    Keep an eye on your seeds to monitor moisture and watch for signs of germination. Your seeds should begin to sprout within one to two weeks of sowing. If using a heat mat, you may see sprouts within a few days.

  5. Turn on Grow Lights

    When seedlings first emerge, it's time to turn on your grow lights. (Or use lights immediately if seeds require light to germinate, like lettuce.) Make sure your lights are the proper distance away from the tops of your seedlings based on the type of grow light you have. Position your light so each seedling is getting the same amount of light. If that's not possible, rotate your trays periodically to help the seedlings grow evenly.

  6. Monitor Seedlings

    Check your seedlings regularly to make sure the growing medium is moist and to watch for issues. If your seedlings look long and leggy or bend toward the light, they're not getting enough light. Move the grow light closer or extend the duration of light exposure your seedlings receive each day.

  7. Harden Off Seedlings

    Before transplanting seedlings outdoors, you'll need to harden them off, or adjust them to conditions outdoors. Begin one to two weeks before transplanting. Leave seedlings outside in the shade for a few hours on a warm day, then gradually extend their outside time and the amount of sunlight they get. Keep seedlings indoors on windy or cold days when the temperature goes below 50 degrees. When seedlings are inside during the hardening-off period, leave them under grow lights.

  8. Transplant Seedlings

    When you've hardened off your seedlings, it's time for them live outdoors in your garden. You can use your grow light setup to seed additional successions of garden plants, experiment with using them on your houseplants, or put them away until it's time to start seeds indoors again next year.