Seed starting under fluorescent lights
From Tiny Farm Wiki
In small farming and home gardening, particularly in shorter season regions, plants are often started early indoors under artificial light, for later transplanting outdoors. Fluorescent light is a popular choice, because it is easy and relatively inexpensive to set-up and run, compared to other indoor light sources for seed starting.
IMPORTANT NOTE: All of this relates specifically to raising seedlings headed for transplanting outdoors. The goal is to use artificial light for as short a period as possible. The lighting situation is TOTALLY different if you're trying to maintain plants for long periods, or entirely, indoors. For indoor growing, much more care has to be taken with light quality and intensity!!
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[edit] Which crops to start?
Many crops benefit from being started indoors, and the more so the shorter your regular growing season. The list includes tomatoes, eggplant, peppers, broccoli, cauliflower, cabbage, Brussels sprouts, tomatillos, melons, summer and winter squash, cucumbers, leek, onion, okra.
You can start just about any vegetable or herb indoors. Many crops that are not recommended for transplanting in various garden books still do well, so you should experiment whenever you feel that a transplant may help.
It's usually not worth starting crops that are planted quite densely and grow quickly when direct seeded in appropriate conditions. These include corn, peas and beans. The large number of transplants required for a market garden make transplants a costlier route. On a smaller scale, like a backyard garden, that's not such an obstacle.
[edit] Quality of fluorescent light
[edit] Types of fluorescent light
Regular 48" cool white fluorescent lamps seem to be the popular, effective choice. I've read up a bit on other lighting approaches, and considered moving to high intensity lights (e.g metal halide), but I've stuck with the plain old cool whites. Since I'm only starting seedlings, and trying to get them into outdoor conditions as quickly as possible (the unheated greenhouse, then, transplanting), it's quite a different condition than if was doing winter growing, or growing plants to maturity indoors. I'm just giving 'em a headstart.
Trying for "full spectrum" light: The basic science is that plants apparently need light in the blue spectrum for vegetative growth (leafy greens!), and red light for flowering and fruiting, so the ideal artificial light source would provide both of these in proper intensity. It gets way more complex than that, but again, all this really applies if you're trying to maintain plants under artificial light, not just start them.
Some people recommend mixing cool white (blue spectrum) and warm white (more in the red range). I tried this for a couple of years: one cool white and one warm white in each two-tube fixture. I noticed no difference. Thing is, fluorescent tubes are such a weak, poor substitute for SUN in any case, that light INTENSITY is the key factor, and this color mixing I found to be an unnecessary extra complication (stocking both types of bulb, rotating trays so they'd get even time on the redder side and bluer side,...) and I didn't notice any difference whatsoever in any of the veggies and herbs I started. Some further indication that cool white is all you need here: Fluorescent Lights for Plant Growth.
Then there are the special "full-spectrum" fluorescent grow lights, which haven't sounded even worth trying (so I haven't). They seem more expensive than they're worth, for the same reason as above.
[edit] High-intensity lighting
I've also thought about upgrading to high-intensity grow lights, like metal-halide, where the intensity is much better. But again, I think all of this is only a big factor if you're trying to mature plants in artificial light, like 100% indoor plants or winter greenhouse growing. For seedlings that'll be heading outside, on the small scale, cool white fluorescents seems to be the most inexpensively effective route.
I experimented for two years with reflectors to increase the overall light on the plants. This is often recommended. I first tried aluminum foil glued to foamcore (like, cardboard), and then bought a roll of Mylar, which is that mirror plastic sheeting (got mine from hydroponics catalog). I tried different tenting set-ups, and hanging from the sides of the rack. The light level seemed higher, but I noticed really no difference in the seedlings, they still stretched towards the bulbs. So I haven't bothered in the last couple of years. This year, I have a plant light meter (just for fun!), so I will try to measure and see what reflectors really do.
Fluorescent light fixtures: Over the last couple of years, T-8 fixtures have been replacing T-12. T-8's are narrower, use less electricity, produce more light, AND they emit pretty even light for the length of the tube. That last bit is the most interesting for seedling production. The old T-12s provide way more light intensity in the middle of the tube: even 2-3 weeks into seedling production, you can see significant growth difference between seedlings near the center and those near the ends of the tube. So T-8s are better much better in that respect. However, I've been told by someone who maintains a school that partially converted to T-8's a few years back, that they don't last nearly as long as T-12s. And the fixtures and tubes are more expensive.
The even newer T5 fixtures come in standard and high output configurations, and offer advantages for seed starting, like more light! They're still expensive, compared to T12 and T8, but worth checking out, either for now or in the future when prices will likely drop.
If you have a choice of fixtures that fit your budget, look for ones that have a more open reflector, and the widest separation between the two tubes. Around here, the standard shoplight fixture has two tubes close together, which concentrates light on an unusefully narrow area. Of the narrow-spaced ones, some have reflectors that extend below the level of the bulb, which concentrates the light even more directly below. Since you're working so close, you want to have light going to the sides. I recently found a hardware store with the older style fixtures, with two tubes well-spaced, and these would be WAY better than what I have, my new rack this year will have them.
This is all common sense based on a little experience. If you're into a little more of the how and why to make sense of things, here's one web page that goes into a fair bit of practical scientific detail, seems to make sense, and is fairly quick and painless to read: Light and Plants.
[edit] Managing germination and small seedlings under lights
Most (North American) common garden veggies are covered when seeding, and can germinate in little or no light. They need moisture and heat. Soil temperature of around 70°F is optimum for most, so if your room is 65-70, you should be fine.
Putting clear plastic over the tray or pot (in these seed-starting photos, you'll see the plastic I use) keeps the moisture in, so you usually don't have to rewet until germination (or for at least a week), but always check! Some people put a few holes in the plastic to allow air circulation, but I don't, I lift it up to peek every day, and don't seal the edges. The plastic also creates a greenhouse effect, trapping heat from the lights and heating up the soil a bit more. Plastic does about the same thing as those clear tray covers.
Oh, you also want to remove plastic as soon as germination starts, because it's not good to keep seedlings and the soil surface too wet and humid, that can promote...disease.
As long as you're clear on the effect of plastic—retain moisture, increase soil temperature—common sense and keeping an eye on things should guide you well.
[edit] Light intensity and distance from plants
Regular 32W or 40W fluorescent lamps are quite weak. Comparison with the sun is quite complicated (you can find lots of good articles online). For one, it has to do not only with intensity, but usable spectrum. Basically, though, you have to keep fluorescents quite close or the plants will stretch towards it. 2-4" is usually recommended and works out well for me.
Keeping the lights really close is important. Every inch of distance significantly reduces the intensity. I try to keep them 2-3" (5-7.5cm) or so, but usually have to raise them to cover more area. Fluorescents are cool, they won't burn plants even if they touch the leaves.
Once the seedlings start growing, unless they're in small pots or flats that fit directly under the lights, the plants right under the lights will grow faster than the ones on the edges, and as you raise the lights from them, the ones on the edges start getting further away. It sounds more complicated than it is. But keep in mind that even an inch added distance from the light makes a measurable difference. So, you just figure out height adjustments as you go, and probably rotate trays every day or two if you can to try and give all seedlings the same amount of light. Or you can install more lights.
[edit] How long under lights?
Overall, try to keep seedlings under lights for the least possible time. Instead of starting a tomato at 8 weeks, try starting it at 6. For many veggies, the extra growth indoors may produce a bigger, nicer-looking seedling, BUT, this doesn't necessarily translate into faster growth in the garden. The longer a plant is in less than ideal conditions (cramped, relatively weak light), the more adjusting it has to do when it gets set free!
It's really pretty simple, especially once you're been through it once. If something doesn't seem to be working out, don't hesitate to plant some more. It's almost never too late to start things...late, even if it's way after the recommended starting dates.
