Growing with T12 Fluorescent Lights

Now that the season for sowing begins, many gardeners will think about how best to light their plants. A bright windowsill will do, but you’ll find that you get better results (faster germination, more uniform growth, etc.) under artificial light, especially if you need to start seeds very early in the season when the days are still under 12 hours a day. And you can also use artificial light to grow plants all year round: African violets, orchids, bonsais, ferns: you name it! They all grow beautifully under artificial light.

Growing with T12 Fluorescent Lights

Fluorescent lights are still the easiest garden lights for novice gardeners, and also the cheapest. Simply hang a fluorescent lamp about six to eight inches above the plant or seed tray, turn it on, and you’re ready to go!

Any fluorescent lamp can be used to light houseplants, but ideally, I suggest buying a 4 foot (120 cm) long workshop lamp with two tubes. Why?

First, 4 feet is the standard length for a fluorescent lamp. This means that a 4-foot lamp costs less than a 2-foot lamp…. And replacement tubes are cheaper, too.

Second, a single tube doesn’t give off enough light for most plants, but 2 tubes side by side do.

Third, a workshop fluorescent lamp is by definition designed to be hung from chains (making it easy to install and easy to adjust its placement) and includes a reflector that directs the light downward, concentrating the light your plants receive. This way you get more light for your money.

Finally, workshop lamps of this type are among the cheapest fluorescent lamps on the market.

The traditional choice of tubes (and the ones I use myself) for growing houseplants is a Cool White (CC) tube (excellent for growth and foliage) and a Warm White (WW) tube (they help stimulate flowering). However, Warm White tubes also tend to promote etiolation (“stretching”). So if you intend to use your lamps only to start seeds, it’s best to use 2 cool white tubes per lamp, as you’ll get more compact plants. You won’t want your seedlings to flower indoors anyway: they’ll transplant better to outdoor conditions before they start flowering.

What about horticultural tubes? There are legions of them… But you won’t find many home gardeners using them. Looking for high quality full spectrum light (which they usually promise), they trade lower intensity for higher quality, but most plants do better with more intense light, even if it’s perfect quality. They are also expensive, often very expensive. Ask other gardening enthusiasts: you’ll find that most use CC tubes for seedlings and CC/WW combinations for growing and flowering houseplants.

Add an inexpensive timer to all of this. Typically, 14 to 16 hour days are suitable for most plants, both seedlings and houseplants. The longer days help mimic summer sun and provide better growth.

What technique should be used?

Now for the important question: what type of fluorescent lamp should you buy?

When I started gardening indoors 40 years ago, it was an easy choice: there was only one common type of lamp: the T12 (tube dimensions are measured in 1/8 inch, so T12 means the tube is 12/8 inch in diameter (1-1/2 inches/3.8 cm). This is the fluorescent lamp you see in offices, department stores, and supermarkets around the world.

However, in the last 15 years, two other types of lamps have become popular: the thinner T8 tube (1 inch/2.5 cm) and the very thin T5 (5/8 inch/1.6 cm). Let’s leave the T8s aside, as they are not yet widely used in indoor horticulture. The T5s, on the other hand, are on the rise in our field. These are the most efficient fluorescent tubes currently in use. They give off more light than the others while using less electricity. (Each type of tube needs its own lamp, by the way: you can’t take your old T12 lamp and just put in T5 tubes!)

Personally, even though many growers have adopted T5 tubes in recent years, I still see a place for the older T12 tubes in indoor horticulture. Because the construction industry has not yet widely adopted T5 technology, T5s remain more expensive than T12s in all phases: lamps, tubes, and replacement ballasts. So even if T12s use more electricity, it would still take years to pay for them. If you only use fluorescents to start seeds indoors, for about 3 months a year, you would probably never recoup the cost difference.

Will T5s remain the best technology for indoor horticulture? My guess is that they won’t. LED lights are still much more efficient than T5s and last almost forever. I suspect that T5s will be replaced by LED lamps as gardening tools in the relatively near future.

But not just yet! There are LED gardening lights on the market, but their price is prohibitive. As in hundreds of dollars per lamp! Plus, the magenta light they emit is very unpleasant to the eye and distorts the color of the plants growing under them. Imagine: Your seedlings look black and the flowers they produce appear purple or gray! Of course, this is only because of the magenta light that is emitted: Once you put LED plants under natural light, you’ll see their true colors. But still, it’s disconcerting not to be able to see how your plants are doing. And if something is wrong with a plant, even if it’s just a lack of water, you’ll have a hard time noticing: it’s very difficult to clearly see a plant growing under LEDs.

For these two reasons (exorbitant cost and lack of visual appeal), I don’t consider the currently available LED horticultural lights to be a real option for the average home gardener…. but I remain convinced that interesting LED horticultural lights (or something similar) that are affordable and provide more natural lighting will soon emerge and become the plant lights of the future. Plus, we’ve seen other types of LED lighting go from prohibitively expensive to insanely cheap in recent years, and I see no reason why plant lighting won’t follow suit.

What should you do?

If you’re a beginner and just want to start seeds under lights, I suggest going with traditional T12 fluorescent bulbs, which are available everywhere at a low price.

Even if you already have T12 lamps, I would stick with that technology for now: upgrading to T5 will cost too much and, as mentioned, I suspect it won’t last long.

However, if you are new to indoor greenery and want to grow houseplants under lights year round (African violets, orchids, etc.), I think the T5s would be a worthwhile investment. The same is true if you need to replace a ballast on an old T12 lamp. Just go straight to a new T5 lamp.

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