Artificial Lighting for your Plants

With seed-starting season upon us, lots of gardeners will be thinking about how best to light their plants. A bright windowsill will do, but you’ll find you’ll get better results (faster germination, more even growth, etc.) under artificial light, especially if you have to start seeds very early in the season, when days are still below 12 hours a day. And you can also use artificial light to grow plants all year long: African violets, orchids, bonsais, ferns: you name it! They all grow wonderfully under artificial light.

Fluorescent lamps remain the easiest horticultural lamps for novice gardeners and also the least expensive. Just hang a fluorescent lamp about 6 to 12 inches (15 to 30 cm) above the plant or seed tray, turn it on, and you’re off to the races!

Any fluorescent lamp can be used to illuminate indoor plants, but ideally I suggest buying a 4-foot (120 cm) two-tube workshop-type lamp. Why?

First, 4 feet is the standard length for a fluorescent lamp. That means that a 4-foot lamp will cost less than even a 2-foot lamp… and replacement tubes will also be cheaper.

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

Thirdly, by definition, a workshop fluorescent lamp is designed to hang from chains (making it easy to install and its placement easy to adjust) and includes a reflector that directs light downward and thus concentrates the light your plants will receive. So you get more bang for your buck.

Finally, workshop lamps of this type are among the least expensive fluorescent lamps available.

The traditional choice of tubes (and the one I use myself) for growing houseplants is one Cool White (CC) tube (excellent for growth and foliage) and one 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 for starting seeds, it’s best to use 2 Cool White tubes per lamp, as that will give you more compact plants. You won’t want your seedlings to bloom indoors anyway: they transplant better to outdoor conditions before they begin to bloom.

What about horticultural tubes? There are legions of them… but you won’t find many home gardeners using them. In their search for high quality, full spectrum light (which is what they usually promise), they trade off lower intensity for increased quality, yet most plants cope better with more intensive light even if it is of perfect quality. Plus they are expensive, often very expensive. Ask other gardening friends: you’ll find most use CC tubes for seedlings and CC/WW combinations for growing and flowering houseplants.

Add to all the above a cheap timer. Normally, 14 to 16 hours days are suitable for most plants, both seedlings and houseplants. The longer days helps imitate summer sun and give better growth.

What Technology to Use? 

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

When I started gardening indoors 40 years ago, that was an easy choice: there was only one common type of lamp: the T12 (tube dimensions are measured in 1/8 inches, so T12 means the tube is 12/8 of an inch in diameter (1-1/2 inches/3,8 cm). This is the fluorescent lamp seen in offices, department stores, and supermarkets all over the world.

However, over the last 15 years, two other lamp types have become more available: the thinner T8 tube (1 inch/2,5 cm) and the very thin T5 (5/8 inch/1.6 cm). Let’s skip the T8s, as they haven’t been widely adopted in indoor gardening. The T5s, however, are rapidly making inroads in our field. These are the most efficient fluorescents in current use, giving 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 simply insert T5 tubes!)

Personally, although many gardeners have adopted the T5 tubes in the last few years, I still see a place for the older T12 tubes in indoor gardening. Since the construction industry has not yet widely adopted T5 technology, T5s remain more expensive that T12s at all stages: lamps, tubes and replacement ballasts. So even if T12s use more electricity, it would still take years of use to break even. If you only use fluorescents for starting seeds indoors, and therefore for only 3 months or so a year, you’d probably never recuperate the cost difference.

Also, will T5s remain the best technology for indoor gardening? I suspect they won’t. LED lamps are much more efficient yet than T5s and last almost eternally. I suspect the T5s will be replaced by LED lamps as gardening tools in the relatively near future.

But not yet! While there are LED horticultural lights on the market, their price is prohibitively expensive. As in hundreds of dollars per lamp! Plus the magenta-colored light they give off is very disagreeable to the eye and distorts the color of the plants that grow under them. Imagine: your seedlings will look black and any flowers produced will appear purple or gray! Of course, this is only because of the magenta light given off: once you place LED-grown 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 there is something wrong with a plant, even 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 those 2 reasons (exorbitant costs and lack of visual appeal), I  don’t consider the currently available LED horticultural lamps a true option for the average home gardener… but I remain convinced that interesting horticultural LED lights (or something similar), affordable and with more natural lighting, will soon emerge and become the plant lights of the future. Also, we’ve seen other types of LED lighting go from prohibitively expensive to insanely cheap over the last years and I see no reason plant lighting won’t follow.

What Should You Do?

If you’re a beginner and only want to start seeds under lights, I suggest going with the traditional T12 fluorescent lamps, available everywhere at a low cost.

Also, if you already have T12 lamps, I’d stay with this technology for now: the conversion to T5 will cost too much and, as mentioned, I suspect it won’t last.

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

But those are my thoughts in 2015. We’ll talk about this again in 10 years and see!

Larry Hodgson
The Laidback Gardener