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Growing Seedlings on a Light Stand

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My first year gardening, I concentrated on annuals. I sketched my plan in February, and, being both frugal and eager, I opted to start several types from seed indoors. My design included a row of sunflowers. The back of the seed packet said to direct sow them around the third week of June, but I forged ahead, planting them in plastic cups on the windowsill around St. Patrick’s Day. By the first of April I had sunflower seedlings—skinny, slouchy seedlings. I tried staking them with drinking straws. Then I consulted Roger Swain. 

The sun in a windowsill may look bright, but its intensity and duration often aren't enough to support strong growth in seedlings.

The sun in a windowsill may look bright, but its intensity and duration often aren't enough to support strong growth in seedlings.

“The word is etiolated,” he said—pale and drawn out due to a lack of light. “Throw them out and direct sow when the ground is warm enough for you to stand on it in your socks.” And so I learned (again) that patience is a virtue. But I also learned the value of artificial light.

How Plants Use Light

Plants make their own fuel, combining carbon dioxide and water to create sugar, which they burn through respiration to power their growth. What powers the manufacture of sugar? Light, in photosynthesis. Different plants require different amounts and intensities of light; for many plants, even these requirements vary over the course of the year, as they move into different stages of growth. In general, though, actively growing plants need 12 to 16 hours of light each day. Seedlings should get 14 to 16 hours. (Think about how much fuel they need to make to support their rapid growth.)

Why a Window Isn’t Always Enough

If you start your seeds indoors, providing enough light can be as difficult as it is important. Because our eyes naturally adjust to compensate for low or high light, it is hard for us to judge the true quality of light in a room. Our eyes work to make light appear even, but its intensity actually diminishes the farther you get from the window. Even if you place seedlings in a south-facing window, you will likely notice them stretching toward the glass rather than growing straight and stocky. The quality of light in a room changes over the course of the seasons, as the earth rotates. The light in any certain season may differ from year to year, as trees outside the window grow taller or buildings are built, creating more shade. Even if a room worked well as a nursery one year, it may not be ideal the next.

Types of Light Bulbs

Use fluorescent bulbs. They are more energy efficient than incandescent bulbs; fluorescents convert a greater percentage of power to light and a lesser percentage to heat than incandescents do. This also means they won’t scorch seedlings or create the warm environment that damping-off fungi relish.

Fluorescent bulbs provide light in the appropriate wavelengths for plants. Plants use the entire spectrum to grow, but the blue range seems to encourage compact growth. The red range speeds growth and may contribute to flowering, which could be important to you if you decide to use your light bulbs for houseplants after your seedlings move outdoors. Both cool-white and warm-white fluorescent bulbs emit light in the blue and red ranges, but in different proportions. However, a warm-white bulb does not provide enough blue light. You can use cool-white bulbs alone for seedlings; pair a cool-white with a warm-white bulb; or pair a cool-white with a “daylight,” or full-spectrum, bulb, which simulates the noon sun. Watts generally correspond to the length of the bulb. The amount of plants you’re growing and the space you have available will determine the wattage/size of your bulbs. Change the bulbs once a year.

Light Stand Design Features

Light stands—the setups that pair seed trays to light bulbs—may be homemade or store-bought. There are simple and elaborate versions within each category. 

Ready-made light stands appeal because they are designed to hold seed trays and to accommodate for seedlings’ growth.

If you go the homemade route, you could simply suspend a shop light over a tabletop, build it a frame out of plastic piping, or attach it to a baker’s rack or other freestanding shelving. 

The top leaves of the seedlings must remain three to five inches from the bulbs as they grow, so you should be able to lower and raise the light bulbs whether you make or buy your light stand. If your setup's bulbs are stationary—or if you are growing several types of plants that grow at different rates—move short seedlings closer to the bulbs by elevating their trays or pots. Shoeboxes and hardcover books make great risers.

Other design features to consider: timers to turn the lights on and off; clear plastic tents, which go over multi-shelf units to increase warmth and humidity; and clip-on fans, which keep air circulating around the seedlings, cutting the risk of fungal diseases.