To grow seedlings hardy enough to withstand a springtime move outdoors, you need to have a direct light source just a few inches away from your seed trays, said Calliope Correia, a horticulture therapist at Fresno State Ornamental Horticulture Nursery at the time of our interview.
Your home’s lamps and other light sources aren’t good candidates because they often can’t be positioned where your baby plants need them, and they might not emit the best light for growth. The winter sun also isn’t an option because it’s too weak, especially when filtered through a window.
“In its natural environment, the plant would be growing with sun all around, so the amount of light that’s coming in through a window is not enough,” Correia said. “The plant will actually stretch out to look for more light—and once it’s too stretched, it’s never going to be a big, healthy plant. So it’s really important to have designated light of some kind during the seedling stage.”
But when you just want to coax a plant to that seedling stage before moving it outdoors to let the warm-weather sun take over, you don’t need to use grow lights specifically. In fact, shop lights may actually be a better choice because of the kind of light they emit.
“The main difference between grow lights and shop lights is that grow lights usually emit just red and blue wavelength light, while shop lights also emit green wavelength light,” Gary Pilarchik, author of The Modern Homestead Garden: Growing Self-sufficiency in Any Size Backyard, said in a video interview. (Pilarchik also dispenses advice on his Instagram account, The Rusted Garden, which is where I first learned about the shop-light hack. I’ve since found similar advice doled out through several university extension offices.)
To photosynthesize, mature plants rely more on red and blue light than green light. (Instead, green light reflects off of them, which is why they look green.) But at the seedling stage, green light—which full-spectrum LED shop lights provide—can be a plus. As University of Minnesota Extension noted, “Typically, plants use more blue and blue-green light when they are seedlings, and more red light later on in their life cycles when they begin to flower and produce seeds.”
Wavelength is just one factor to consider when shopping for a light source, though; the brightness and color temperature of a light matter, too. “Brightness is measured in lumens, while color temperature—how warm or cool a light looks—is measured in kelvins (typically abbreviated on the packaging as ‘K’),” says staff writer Thom Dunn, who wrote our guide to the best LED light bulbs. “Standard incandescent light bulbs and soft white LEDs typically have a color temperature around 2,700 K.” But for proper plant growth, you need something with an even higher color temperature.
According to Pilarchik, any white LED shop lights with a brightness of 5,000 lumens or higher and a color temperature of 5,000 K or higher—like the Hyper Tough shop light—can be used as grow lights for seedlings. (Although Pilarchik sells seedlings and other gardening materials on his website and Amazon, he doesn’t have any financial relationship with Hyper Tough.)
Another knowledgeable gardener I’ve connected with through Instagram, Amanda Nadeau (who goes by @theeverhopefulgardener on social media), has had similarly great results using shop lights with 4,000 lumens and a 4,000 K rating. Following her advice, I’ve also produced healthy starts using these Braun 5500 Lumen 4 ft. Linkable LED Hanging Shop Lights, which have a 4,000 K rating.
Though less attractive than the Hyper Tough shop light, this model has chains that are longer for easier adjustability over seedlings. Even at 4,000 K, these lights nurture seedlings sufficiently indoors for transplantation in the garden. Link up to eight units.
