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Shedding some light on houseplant care

We're entering the dark months. Technically the days are getting longer. But for our psyches and our houseplants, January and February get long and dark indeed.

The parties and busy-ness of the holidays have passed, the snow and ice challenge and tire us out, and our spirits can sink very low. Some people develop the condition we call SAD (seasonal affective disorder). Our houseplants may appear to have it, too.

It is no wonder that the plants are sad. Our so-called houseplants come from all over the world. They may be bulbs, tropical perennials or summer-flowering annuals. They each need a particular duration and intensity of light and humidity, different day-lengths, and different rest periods, to grow or flower. So it's difficult to meet their real needs in an indoor setting; at best we can only come close.

Try keeping a variety of plants and you'll soon learn a lot about imperfect winter conditions, the lighting above all.

>Wrong lighting

When we first take the plants inside in September, they're still thriving from the great summer sunshine and humid air, and look great for awhile. (Only a few drop their leaves from the shock of the change.) But now is when you see the consequences of a few months of deprivation.

Sunlight provides plants with the full color spectrum, from red-orange-yellow to green-blue-violet. Plants use the whole range of light, but the blue (cool) and red (warm) parts of the spectrum are most important.

If plants get too much red light, they grow tall and leggy; blue light keeps them short and stockier. That's why easy foliage plants like philodendrons and snake plants thrive in offices with their typical fluorescent (blue) lighting. But the geranium and impatiens you brought to your desk won't keep flowering under those conditions, as they need a fuller light spectrum.

Poor lighting also produces plant stress, and stress exacerbates disease and insect problems. Plant stress comes from any struggle to live under the wrong conditions, and just as with animals, stress takes its toll.

The stressed person develops hives, heart disease, headaches or myriad other conditions, or recovers less quickly from a setback. Similarly, the stressed houseplant develops scale, whitefly, mealybugs, or succumbs to a disease, much sooner than the thriving, well-lit and humidified specimen.

Stress isn't the actual cause of the specific problem -- the insect egg or the disease spore had to be present in the environment. But stress is a precipitating condition.

Frankly, my schefflera and ficus always get scale around February; I control it somewhat with a natural houseplant product labeled for scale, and then I trust Mother Nature to fix it in the summer on the deck.

In other words, the potential for the problem is always there, but in the bright, humid world of outdoors -- no problem.

>A happier winter

If you have a greenhouse or Florida room, you don't need this article. You have enough light, unless you are starting seedlings or trying to force some plants to flower out of season.

In normal home conditions, most indoor plants really need supplemental lighting, and all benefit from it. A window is usually not enough; a kitchen full of windows may be.

Even full shade outside is usually brighter than your best window. So imagine: If a plant needs full sun to flower in the summer, how well will it like your little window?

Perhaps it's enough for you to have plants that barely survive the winter, but if you want more performance it's time to shop for plant lighting.

>Types of light bulbs

*Incandescent (house lamp) bulbs are too hot for plants. A plant under the old-fashioned reading lamp first gets spindly and then the leaves scorch.

Fortunately for the plants, as well as for energy efficiency, many of us have switched to CFL bulbs (high-quality compact fluorescent light bulbs) for indoor lighting. You can put plants very close to them without burning. One flaw is that much of the light is wasted (from the plant viewpoint), so consider some sort of reflective shades to direct their light.

Fluorescent tubes are still the popular choice of most houseplant collectors and amateur seed-starters, and give twice the light for the energy output. The typically cool office bulbs are enough for most foliage plants, but if you want lots of flowers you should try one cool white and one warm white tube.

Now you can find full-spectrum fluorescent tubes that work well, although they are a bit more expensive. HID (high-intensity discharge lamps) are used by professional growers, but they are costly, use a lot of electricity and produce a lot of heat. Types include metal halide, high-pressure sodium and mercury vapor lights.

>For better lighting

If you have supplemented the natural light with fluorescent tubes, remember not only to turn your plants around but also to switch their positions so they benefit equally. The center of the tubes gives the best light, and the ends put out less and less light as the bulbs age. When the ends are dark and bluish, replace them. It also helps to wash all light bulbs or tubes regularly (when they are off and cool), since the dust you can't see acts as a cloud.

One of the challenges in lighting a collection of houseplants is getting each plant the right distance from the light source. If you're using the "grow light" bulbs, put your hand on leaves nearest the heat source, and if you feel heat, that may be too close for the plant.

Usually people put plants too far from the cooler, fluorescent lights. I fiddle with a series of stools, wire shelves and hooks from the ceiling to get the plants all in their best positions. Then something changes, and I have to move them all over again.

It also pays to know the native light conditions for each plant. A rosemary (Mediterranean, natively) and a Mandevilla from Brazil might need to be 10 inches from a light source, but your dear old Dracaena (an understory shade plant) takes what it gets.

There's more to houseplant culture than light, and there's a lot more to lighting than this overview. Experts know the optimum light intensity for each species, the rest requirements, and the duration of light needed at each point in the growth cycle for plant health and flowering. For us regular folks, suffice it to say our plants probably need more light.


Sally Cunningham is a garden writer, lecturer and consultant.

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