How to Use Grow Lights for a Healthy Indoor Garden

Nobody wants spindly seedlings and leggy houseplants. Here's the best ways to avoid these sad situations with the help of artificial lighting.

While many houseplants do just fine indoors with whatever natural light flows through your windows, certain ones can be coaxed to bloom more reliably, or will grow more healthy leaves, with additional light from artificial sources. And if you're starting vegetable and annual flower seeds indoors, they often need the help of lights to develop properly. While the amazing power of sunlight is tough to completely replicate, using grow light fixtures fitted with simple fluorescent or LED bulbs can come close. Here's what you need to know about setting up the best light systems for your houseplants and seedlings.

several houseplants under a grow light in a kitchen
A mix of houseplants thrive under a grow light. Marty Baldwin

Use Grow Lights for Seedlings

Bright lighting is key to getting a jump start on spring transplants indoors. Most rooms do not provide enough light to produce dense, healthy seedlings. Even a south-facing window often falls short when it comes to the amount of time the sunlight can shine through. Seedlings will usually germinate well and produce their first set of leaves in a sunny window. But then the "stretch" begins as stems reach desperately for more light to fuel their rapid growth.

Prevent leggy plants by growing your seedlings under artificial light created by standard shop lights ($16, Walmart) outfitted with fluorescent tubes or energy-efficient LED bulbs. These bright lights provide a combination of blue and red light waves necessary for good plant growth. Look for bulbs that are "full-spectrum," which your plants will need.

Using Grow Lights for Houseplants and Herbs

Illuminating your favorite blooming houseplant, such as an African violet, will encourage the plant to come into bloom more than it would in just natural indoor light. Likewise, you can use artificial lighting to boost your harvests of basil, rosemary, parsley, and other greens that are easy to grow indoors during the long winter months.

Red light waves spur flowering and fruit production for houseplants and edibles. Choose a light source that provides plenty of rich red wave light. For example, warm white light is deemed 2,700K to 3,200K on the Kelvin color temperature scale, and is rich in red wave light. Look for the Kelvin rating of a bulb on the product packaging.

How Many Hours Should Grow Lights Be On?

Illuminate interior plants for 12-14 hours a day. If you keep the lights on for 16-18 hours a day, flowering plants will likely bloom sooner. Seedlings grow best when supplied with light around the clock. Leaving the lights on 24 hours a day compensates for the lower level of artificial light compared to sunlight. This is when more energy-efficient LED bulbs pay off. Although more expensive to purchase up front, LED bulbs use less power to run and last longer than fluorescent bulbs. A simple mechanical timer ($7, Target) will make using grow lights easier and more efficient.

Tips for Using Grow Lights

Artificial lighting must be very close to the plants to be effective. As rays of light move away from the source, they dim significantly. Keeping the lamps close to plants increases the amount of light received, which keeps seedlings compact, preventing long, weak stems. Position lights 6 inches or so above transplants, moving the lights up as the plants grow, to maintain the 6-inch source-to-plant distance. Indoor plants and edibles grow best when they're within 12 inches or so of the light source.

There are many types of specially designed lights and fixtures for growing plants indoors. A simple setup with fluorescent or LED bulbs ($47, The Home Depot) is perfectly fine for growing seedlings to transplant into your garden. Blooming indoor plants and food crops will benefit from specially designed LED grow lights.

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