Help your houseplants, seedlings, and herbs thrive by giving them the right supplemental lighting.
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Sure, all plants need light, but the amount they need can vary quite a bit. A space with a sunny window may be all your low-light houseplants need to do just fine, but other indoor plants demand brighter, more consistent amounts of light to grow properly. For example, if you're starting veggie seedlings for your spring garden, coaxing a blooming houseplant to produce flowers, or even raising fresh herbs on your kitchen countertop, the right grow light is your friend. Depending on what you're growing, here's what you need to know to choose the best lights for your home and your plants.

indoor green cart lighted with potted plants seedlings and metal watering can
Credit: Peter Krumhardt

Types of Plant Grow Lights

LED and fluorescent bulbs both produce full-spectrum light that plants need to grow. There are many plant light kits on the market that include LED or fluorescent bulbs, but an LED system ($45, The Home Depot) offers several advantages that make them the better choice. For starters, although LED bulbs cost more than fluorescents at purchase time, they use half the electricity fluorescents require and last five times longer than the average fluorescent bulb. They also give off less heat and mercury-free LED tubes don't shatter like glass fluorescent tubes, leading to fewer safety hazards.

Best Lights for Growing Seedlings

Newly emerged seedlings and young plants grow well with the aid of full-spectrum light, which has both blue and red wavelengths. Special LED and fluorescent "grow lights" will work, but so will less expensive fluorescent tube bulbs. Be sure the light source is within 6 inches of the plant foliage for the best results. For easy movement, suspend the fixture on chains or elevate your plants on a table or this DIY seed starting station. To keep your lights working efficiently, gently wipe down the light tubes to remove dust and grime before using them each year.

Best Light for Flowering Plants

Red light waves are essential for spurring plants to flower and growing fruit indoors. Shop for LED bulbs and fixtures that are specifically designed for growing plants. They're usually labeled "grow lights" because they're created to produce a high number of red light waves.

Some electric brands produce plant-friendly LED bulbs called "high-output LEDs." High-output LEDs are generally twice as bright as standard LED grow lights. These ultra-bright lights are excellent for growing plants that are native to sunny, dry climates such as cactus, citrus, rosemary, and geranium. Plan to light flowering and fruiting plants for 16 to 18 hours a day. Place the light source 12 inches or so away from the foliage.

How Much Light Do You Need?

Once you've decided which kind of plant grow light you want, it's time to decide how big a bulb you need for the space you have. First, determine how much space you need to illuminate. As a rule of thumb, aim for 20 to 40 watts per square foot. Divide the wattage of your bulb by 20 (such as 400 watts divided by 20 = 20), and then divide the wattage of your bulb by 40 (400 divided by 40 = 10).

The answer gives you the extremes of your light intensity range. With one 400-watt system, you can light between 10 and 20 square feet of interior landscape. Also, be sure to match the wattage of your bulbs with what your fixture is designed to handle. For example, that 400-watt bulb should not be used in a 250-watt system. Adjust your setup as you observe how well your plants grow. Increase or decrease the intensity of the light by shifting the placement of your plants or light fixture so the plants are closer or farther from the light source.

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