Snapdragons are among the plants that benefit from an early start under lights.
If you've ever tried to grow seedlings in a south-facing window, you know why supplemental light is necessary. Tall, spindly seedlings with floppy stems and pale green leaves are a good indicator that your plants are not getting enough light. Although some gardening books and online sources say that seedlings can be grown in your windowsill, I've never had this work successfully. It could be that in some sunny southern states it actually does work, but here in the Upper Midwest, the natural light from a window just isn't enough. Even a south window will provide only a few hours of direct sunlight and a couple of hours of indirect sunlight, and that's just not enough to grow good plants.
Enter the light cart. I have mine set up in my living room, in a south-facing window where my plants will get a little outdoor light plus artificial light. I'm a thrifty gardener, and plants are expected to pay their own way around here. For this reason, I skipped the expensive light sets advertised in gardening catalogs and purchased a plastic shelving unit at Menards. Because watering is one of my biggest challenges indoors, I turned the shelving unit upside down, which provided a pan-shaped area that catches any overflow from my flats. I use regular 48-inch shop-light fixtures, plugged in to a power strip, which is plugged into a three-prong grounded outlet. Making your own light cart is so ridiculously easy. Here are a few more ways to make sure you get the best seedlings that no money can buy.
The writer uses an inexpensive plastic shelving unit for a light cart.
One of the most affordable options for lighting is also just fine for producing healthy seedlings. Forget about the expensive grow-light bulbs (the violet-tinted ones). They might be better for flowering plants such as African violets, but are not needed for seedlings that are vegetative or leafy. Fluorescent bulbs come in several options, including warm-white (a pinkish or tan color) and cool-white (bluish white color). It's a little better to use one cool-white and one warm-white lightbulb, because they provide a wider spectrum of light. Fluorescent lights come very close to duplicating natural light from the sun. Don't use incandescent lights, which are mostly red light and produce a great deal of heat in proportion to their light output.
In order to fool your plants into thinking it's spring, you'll need to leave your lights on for 14 to 16 hours daily. This duplicates the light levels that they'd get during May and June. I turn my light set on as soon as I wake up in the morning, calling out “wake up little guys,” and turn it off when I go to bed at night. If you're the forgetful type, you can purchase a timer for the lights. Nothing terrible will happen if you forget to turn them off, but the plants will appreciate a rest period while they go through important metabolic processes.
Light levels are highest close to the bulbs, so keep them just a few inches away from the plants. Fluorescent lights are cool, so little, if any, damage will occur to the plants should a leaf accidentally touch them. Your lights will function best if they are clean (dust yearly), limit the number of times you turn them off and on, and don't let the ambient room temperature go too low (keep it above 50 F).
T12, T8 and T5 Fluorescent Bulbs
It turns out that fluorescent bulbs come in a range of options, like everything else these days. T12 bulb is the older-style bulb, the kind that's been around for a long time. Although cutting edge in its day, it is being replaced by the T8 bulb. This is much more energy efficient, as well as brighter, and is easily spotted because it is skinnier than the regular T12. A T8 bulb will work in a regular light fixture and can be purchased at most hardware stores.
The T5 bulb goes one step further in efficiency. It uses about the same amount of watts per foot as the old T12 bulb, but is approximately twice as bright. The bad news is that for now, T5 requires a special fixture and is not available in longer lengths at your local hardware store. Online, find them by searching for “GE Starcoat T5 HO Fluorescent Lamps.” I’ve noticed that some seed catalogs, which also sell equipment, offer T5 bulbs as part of their grow-light set-ups.
Keep the fluorescent lights a couple of inches away from the plants. Move the lights up as the plants grow.
Over the years, watering has been one of my biggest stumbling blocks. Watering cans tend to distribute water evenly over all surfaces, including ones that shouldn’t get wet. That might not be a big deal if your light cart is in the basement on a concrete floor, but since mine's in my living room, I can't spill very much before I have a huge mess. Bottom watering is a good option, but don't let your plants sit in water for very long, or you'll have problems with root rot. The other option is to remove the flats to a sink or bathtub and water them there. Either way, it's a bit of a hassle.
Professional growers sometimes talk about "air pruning" their roots. This just means that they allow some airflow underneath their flats. The roots will stop growing when they encounter the air gap. This prevents the well-known problem where roots grow out of their containers and form a mass hanging at the bottom of the plant. Ripping off these roots during the transplanting process can be hard on the plant. To create an air gap, you can support your flats using PVC rails or another building material such as wire screens.
Joe Schmitt, a professional flower grower in Madison Wis., uses a large-scale grow-light setup in his basement. He produces thousands of seedlings annually.
While you're checking and watering your plants, it's not a bad idea to rotate them. If the light from your fluorescent lightbulbs is a little uneven, you frequently end up with plants leaning in toward the center of the light fixture. By rotating the flats, you can achieve more even growth. This also gives you a chance to notice any problems and address them right away.
Of course, the best reason to start plants from seed under lights is that it’s fun. Watching young plants grow is a good way to chase your winter blues away and welcome the season.
A version of this article appeared in a March 2014 edition of the State-by-State Gardening eNewsletter.
Photography courtesy of Erika Jensen and Joe Schmitt.