Gardening under Lights
Not even the most enthusiastic Newfoundland patriots among us would claim that ours is the optimum climate for year-round gardening. Let's call it for what it is: five months of delight, except for the black-flies, followed by seven months of staring out the window at the rain and snow.
At times like this, one often considers growing plants under lights indoors. Wouldn't it be perfect to come into the Newfoundland Horticultural Society meeting next February with an armful of red roses freshly-picked from my basement. That would make the members green with envy!
O.K. It's time for a reality check. One can grow plants under lights but artificial illumination is never as good as old-fashioned sunlight. Even throwing technology at the problem does not always work as our trusty and well-beloved ex-Premier Peckford and his evil henchman Dr. Sprung found out to their chagrin. Fortunately they didn't have to pick up the tab personally for their foiled experiment.
All this having been said, one can garden quite successfully with artificial light; the secret is in the answers to two questions: Why is grass green? and Why are far-off street lights less bright? Plants, of course, use light as a source of energy but some light is better than others. Blue and red light is particularly valued but green light is useless. Plants are green because they absorb the colours in the spectrum except green light which they reject. It follows that artificial lights should have major blue and red components and little or no green. Such a colour mix seems harsh and unpleasant to us, but plants love it.
Fluorescent lamps are what amateur gardeners usually use, so let's talk about them. There are two Schools of Opinion: one swears by Grow-Lux (Sylvania) or Plant-Gm (Westinghouse) tubes, the other declares them to be a waste of money and uses regular domestic fluorescent tubes. I suggest a compromise; use both the special plant growth tubes and domestic cool white tubes in equal proportion. It is important, though, to realize that light production from fluorescent tubes drops off rapidly with time. Our eyes have a built-in system to adjust for changes in light intensity so we don't notice the drop-off in light output until the tubes have almost reached the point of failure. Plants do notice!
A good general rule is that the best subjects are plants whose foliage is between six and ten inches from the light source and don't have upper leaves shading the ones below. Dwarf cacti do quite well under lights because they meet these criteria exactly and can even be placed closer than six inches. Ferns also do well but are prone to scorching if the air is too dry.
Some people even grow salad crops under lights.
A frequently-heard suggestion from the experts is that fluorescent tubes should be replaced every 12 months, even if they seem perfect to our eyes. Light intensity is also determined by the distance between the plants and the light source: a plant that is 12 inches away from a light source does not receive half of the light intensity available at 6 inches; it receives only a quarter. The physics rule is that light intensity drops off proportionally to the square of the distance.
The moral is that plants should be grown as close as possible to the lights without burning. Rosette plants with compact growth, such as African violets, are perfect for growing under lights. On the other hand, taller-growing plants, such as Impatiens [and cucumbers!], do less well because only the upper leaves are close enough to the lights to derive much benefit.
How long should lights be left on? Surely, plants would relish 24 hours a day of illumination? Actually, most plants we grow indoors (our so-called house plants) come from tropical regions where the day-length never exceeds 12-14 hours. Many tropical plants have physiologically adapted to this regime and they pine away if the day length is too long. Just as we would! A 12-hour day is generally optimum for growing most house plants but some species grown for their flowers do better with longer days, up to 16-18 hours. Only plants adapted to living at the North Pole would enjoy a 24-hour day and there are not many of them!
It follows from all of this that timer is necessary. The general purpose timers available from hardware stores work perfectly well. Purists insist that these timers are designed for resistive loads (incandescent lamps) and should not be used for fluorescent tubes that use inductive starters. I have never found a problem but I recommend a reliable heavy duty timer, not one of those $5 specials.
And that is really all there is to it. Some plants will do well, others will not. Some are worth the space, others are not' Anyway it is fun trying to grow them and it beats staring out the window at the snow.
Dr. Ron Payne