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photo courtesy of the AOS

Paphiopedilums are among those genera
that adapt easily to life under fluorescent
lights. Here, a specimen grown by Ken Smeltz
and his late wife, Marie: Paphiopedilum
'Kenmar', AM/AOS.

Fluorescent Light Gardening

Kenneth C. Smeltz


Where natural light is limited consider raising orchids under fluorescent lights. Convenience, climate control and reduced costs are among its advantages.

Twenty-one years ago, my wife, Marie, and I started growing orchids under four fluorescent tubes. Today, there are 49 tubes, ranging in length from 2 feet to 8 feet, hanging in the basement illuminating a 125-square-foot area. Among the orchids are 380 phalaenopsis, 170 paphiopedilums and about 50 assorted orchids - tolumnias, angraecums, aerangis, miniature cattleyas, eurychones, Amesiella philippinensis, Chiloschista usneoides, Leochilus oncidioides, Ornithocephalus and Howeara Mini Primi.

Growing under fluorescent lights requires more specific conditions than those prescribed for gardening outdoors or in a greenhouse. After all, there is sunshine every day.

The Light Source Since we began growing orchids under lights, a number of light sources other than fluorescent tubes have become available. However, the height of our basement ceiling, the number of new units necessary to light our growing area, the cost of the change and other factors precludes our switching from fluorescent lights.

Several combinations of fluorescent tubes are possible. I prefer those labeled full spectrum. These give off white light and have a spectrum resembling that of sunlight. Though rather expensive, they last about 18 months to two years. When guests enter our basement, they often comment on how bright it is. But this is relative. One can get only 800 to 1,000 foot-candles as measured by a GE-type 214 light meter right under the tubes and in the center of a mass of tubes. Two hundred and fifty to 450 foot-candles are measured near the tops of the leaves. The length of time these lights operate depends on the time of year: 14 1/2 to 15 hours for winter, 15 1/2 hours for spring and autumn, and 16 hours for summer. Six timers turn the lights on and off. The distance between the tubes and the top leaves of the phalaenopsis varies from 8 to 20 inches. Paphiopedilums are positioned 14 to 20 inches beneath the tubes.

Photo courtesy of the AOS

Phalaenopsis in flower flood the main isle
of the author's light garden with color.

Temperature The plants are near a gas-fired, forced-hot-air furnace and gas-fired hot water heater. In addition, heat is generated by the 28 ballasts that service the 49 fluorescent tubes. These heat sources maintain a temperature of 72 to 74F in winter during the day and 68 to 69F in the rest of the house. At night the thermostat is lowered to 58F. If the outside temperature is predicted to be no lower than 30F, window in the basement is opened and a fan draws air in from the outside. This create a 58 to 62F night temperature. Such manipulations in the autumn give us great differentials because the day temperatures are 70 to 75F. Summer presents a problem. We keep as many doors and windows open as possible or use the whole-house air conditioner to cool the space. This gives 78 to 90F day temperatures and 72 to 75F a night.

Air movement is equally as important as any other environmental factor. The air in the basement is moved by six strategically located fans (not including the fan at the window) that operate 24 hours every day.

Left: Paph. Aylingii 'Kenmar', HCC/AOS
Amesiella philippinensis can be grown under lights.

Containers and Media All paphiopedilums are in plastic containers. The potting mix is

4 parts of a local commercial grower's paphiopedilum mix (3 fine to 1 medium Douglas fir bark, small perlite, bone meal, granulated limestone, charcoal, organic fertilizer and Green Sand)
1 part medium fir bark
1 part redwood bark cut to 1/4 to 1/2 -inch size
1 part large coarse perlite
1/2 part "chicken grits" (chopped oyster shells, about 1/8 to 1/4 inch in diameter).

Where quality water is available, less-complicated mixes may suffice. At Longwood Gardens, where I volunteer, paphiopedilums are rooted in a mixture of equal parts charcoal and fir bark, and watered with well water.

The phalaenopsis are in plastic containers, too. The potting medium depends on the container size and age of the plant. New Zealand sphagnum moss is used for seedlings in containers 4 inches or less in diameter. Sprinkling a thin layer of small, granulated charcoal on top of the moss prevents algae from forming. This works if these pots are hand watered. If they are to be watered and fed with a watering wand at line pressure, an additional layer of clean gravel is sprinkled on the charcoal to keep it from being washed away. Larger containers are filled with a mix of equal parts medium-size Douglas fir bark and charcoal. When the pH of our municipal water rises above seven, redwood bark is added to the fir bark. For many years, we used chopped gum balls (seed capsules) from the sweet gum tree (Liquidambar styraciflua) with great success. These were gathered right after they had fallen to the ground and chopped in a hammer-mill-type shredder; a spinning blade shredder did not work.


Tolumnias, at home beneath fluroescent
lights, grew so large they ahd to be moved
to their own set of lights

Fertilizing Phalaenopsis and hanging plants are fed on a regular schedule: on a day-to-day basis of water/spray/water/ spray/feed/spray and repeat. We use room-temperature water from a mixing valve placed between the hot- and cold-water lines. Peters 20-10-20 is diluted to give 75 to 125 parts per million nitrogen. Because these plants are on two-tiered benches covered with 1/2-inch wire mesh, a watering wand is used both for watering and feeding (using a 50 to 1 M.P. Mixer Proportioner). Both the excess water and dilute fertilizer solutions drain onto an assortment of tropical foliage plants. Although these are beneath the benches and receive only 15 to 35 foot-candles of light, they have grown into a veritable jungle. Maintained in clay pots, these plants sit on a layer of TerraGreen baked clay that covers the cement floor. The baked clay is porous and retains a great deal of water. This increases the humidity in the basement, where the relative humidity varies from 50 to 60 percent in the winter and 60 to 68 percent in the summer. The excess water and fertilizer drain into a sump where a pump diverts the liquids outside.

Containers holding paphiopedilums and seedling phalaenopsis are set on stainless-steel trays containing pebbles and plastic "egg crate" (used under fluorescent lights to diffuse the light). Water covering most of the pebbles in the tray evaporates to bathe the plants with humidity. The water level is kept near or at the bottom of the egg crate. This allows air to circulate around and through the containers.

Paphiopedilums are fed one week followed by watering. This alternating schedule gives two waterings and two applications of Peters 20-10-20 (diluted at 1/2 teaspoon per gallon water) each month Most of the time on the remaining days, the plants are sprayed fairly heavily with water from a pump sprayer. When these plants are watered or fed, each pot is placed in an appropriate container and the water or fertilizer is poured from a watering can onto the potting mix. The effluent is discarded. Keep fertilizer off the leaves. If any gets on the foliage, wipe it off immediately with a paper towel. This may seem like a lot of work and excess tender loving care, but it has paid tremendous dividends - no leaf or crown rot, lots of flowers and big, healthy plants.


Water Quality Mention watering and most individuals think of how, how often and to what degree, among other factors. But questions are rarely asked about water quality. This is more important than all of the other water questions combined, especially if orchids are irrigated with municipal water. Based on the Congressional Clean Water Act, the Environmental Protection Agency on June 7, 1991, sent out an edict for all municipal water companies to reduce the lead and copper levels in their water to extremely low amounts. Depending on the age of the pipes and other conditions, pH (hydrogen ion concentration) plays an important role in this situation. Without telling anyone or understanding the ramifications of their actions, the municipal water companies raised the pH to as high as 8 or possibly higher. When chlorine is now passed into this water for disinfection, hypochlorite ions are formed, and depending on the base used, a metal hypochlorite is now present. Since sodium hypochlorite is the basis for commercial Clorox, we now have a dilute solution of Clorox or a relative thereof.


The slightly acid-loving orchids began dying, especially the tolumnnias and other plants attached to cork plaques. Top leaves on the phalaenopsis turned yellow. Soon whole plants were dead. Acidification of the water with sulfuric or phosphoric acids to pH 5.8 to 6.8 helped, but the increase of salts in the water was harmful to the orchids. Today, the tap water's pH is about 6.8 to 7.0 and is used for all watering and feeding of the phalaenopsis and hanging plants tended with the watering wand. The plants have stopped dying and are improving. For the pump sprayer, a 50:50 combination of rain water and excellent well water is used and the plants respond favorably. To learn more about water quality, read chapters four and five in Bob Gordon's Orchid Seedling Care (Laid-Back Publications, Rialto. 1991).

Insect Control Do not use chemical pesticides in the house. Do not hang chemical pest strips in the house. There is a good chance these contain Vapona, a substance that is supposed to attack the insects' nervous systems. In addition, avoid applying Cygon 2E, because it can cause health problems. Control insects with Sun Spray Ultra-Fine Horticultural Spray Oil. This is relatively non-volatile and non-toxic. When applied in the proper manner - including agitation when in use and hitting insects directly with the spray - it is effective for aphids, fungus gnats, mealy bugs, mites, scales and spider mites. Before spraying hard-shell scales, first flick the scale off the plant and then spray to kill the crawlers that were under the shell. There is a simple and safe way to control fungus gnats and other flying insects where heavy watering is not done. Place small yellow cups, buckets or small tubs throughout the orchid collection. Fill each container with water and six to seven drops of Physan 20. This algaecide also has the necessary detergent properties to get the oil off the insect and help it die by drowning. Add more water as the liquid in the containers evaporates. Yellow sticky strips are not used because of some light blockage.

When the cold winds howl and snow blankets the ground, it is wonderful to be able to walk down to this tropical haven. It inspires even more enthusiasm for orchids.

- Kenneth C. Smeltz dedicates this article to his late wife, Marie, who was the better half of the growing team responsible for AOS-awarded orchids bearing the clonal name 'Kenmar'. These award-winning orchids were raised beneath fluorescent lights. 1021 Crestover Road, Wilmington, Delaware 19802.


1Potinara Cherub is now correctly, Rhyncattleanthe Cherub.