It is a common scenario: the windowsills are overflowing with orchids and a greenhouse is out of the question. The solution: Grow orchids under HID (high-intensity-discharge) lights.

In my HID light garden, a diversity of orchids are cultivated beneath these lights. Full-size vandas (including some with multiple spikes and semiterete varieties), cattleyas and tall cane-like dendrobiums thrive within 3 feet of dainty, shade-loving pleurothallids and cloud-forest dendrobiums from New Guinea. Subtle differences in illumination and temperature create microclimates that cater to the needs of different genera.

Choosing a System

Homeowners who consider light gardens often zero in on fluorescent lights. But HID lighting is an alternative that is gaining popularity where a spare room, a large closet or even an unused area of the basement is available. Fluorescent lights are a boon to the orchid grower. But these bulbs provide insufficient light to flower those orchids that demand high illumination. While modern fluorescent lighting that offers a spectrum coverage comparable to the sun is available, the tubes lack sufficient output in lumens to coax a big vanda or dendrobium to reach its full bloom potential.

Several HID-type lights are available. Metal-halide lamps match the tropical sun's color spectrum more closely than other HID lamps and are the best for vegetative growth and development (Figure 1). High-pressure-sodium lamps are somewhat more cost effective and help increase flowering, but their spectrum is more limited. They are better utilized as a supplement to metal-halide lamps (Figure 2). High-pressure-sodium lights are also effective when positioned to supplement natural sunlight in a greenhouse. Low-pressure-sodium lights are of limited utility due to their narrow yellow spectrum.

Mixing metal-halide and high-pressure-sodium tubes achieves the best lighting environment. HID lights deliver much more light in lumens than fluorescent lights per watt of output (Figure 3). They are available in 150-, 175-, 250-, 400- and 1000-watt systems. Bulbs placed horizontally deliver more light to the plants than those placed vertically. For safety and peace of mind, be sure that any system purchased is UL (Underwriters Laboratories) approved.

Light Movers

To illuminate a larger area with only one or two bulbs, invest in a light mover. It will provide more even distribution of light and cast virtually no shadows. This moves the light fixture back and forth along a 4-, 6- or 8-foot rail (Figure 4). Two lights can be positioned end-to-end to extend the rail up to 16 feet or create a circle (Figure 5). The mobile lights can accommodate more plants than stationary fixtures. For every foot light travels from the source, the intensity decreases significantly (Figure 6). A light mover permits installation of lamps so that they will deliver the maximum amount of light to the greatest number of plants over the shortest distance.

A light mover will also reduce the heat cast from the tubes onto the foliage below. The heat intensity generated by HID lights is considerably more intense than fluorescent lights; a plant set within 6 or 12 inches of stationary HID bulbs will burn. But those beneath mobile fixtures can be set closer without harm. For example, a vanda that can be 3 or 4 inches away from a mobile HID unit would need to be set 24 or 30 inches beneath a stationary one. Experiment to determine the distance between bulbs and plants. Touch the foliage; if it is hot, move the plant away from the light. A pink cast to the foliage or a red margin around the leaves indicates excessive illumination.

Maintain the system to ensure it operates properly. Twice a year, wipe the tracks with a paper towel or cloth moistened with T-9 or a similar marine lubricant. Inspect the motor. New models contain self-lubricating bearings, but some old models do not. If you purchase a used system, it may be necessary to lubricate the bearings yourself. Keep the system in shape to prevent any breakdowns that could leave the light stranded on the track and damage the plants below.

To assemble a moderate starter set-up that will adequately cover a 10 x 10 foot growing area, assemble these supplies:

An initial investment of $ 1,000 for this type of set-up is realistic. These lights operate on 110 current and should be on their own circuit. Anyone lacking electrical expertise is encouraged to hire an electrician to make the necessary modifications. It is easy to determine the impact operating these lights will have on your electric bill. One thousand watts is equal to one kilowatt. Electric bills are calculated in kilowatt hours. Therefore, a 1000-watt bulb that burns for 12 hours per day will add 12 kilowatt hours per day to the bill. A 400-watt fixture will use 5.6 kilowatt hours.

My primary growing environment consists of a 10 x 18 foot portion of a converted garage that includes a 1000-watt metal-halide unit on a 6-foot light mover set end-to-end with a 400-watt high-pressure sodium unit on a 6-foot light mover. Plants in containers are positioned on benches; those on plaques are suspended from wire mesh attached to the wall. The majority are in slatted baskets suspended from chains near the ceiling. A stationary 250-watt metal-halide light and a four-tier light cart with fluorescent lights supplement the HID lighting. About 1,000 orchids are in this area.

The room is illuminated the same number of hours as outdoors. This ranges from 11 hours in the winter to 18 hours in the summer. Every two weeks, the timer is adjusted at 15-minute increments.

For anyone on a budget, or with a smaller area to illuminate, there are kits available through dealers that take the guesswork out of assembling a HID light garden. Some are in attractive cases and finishes that blend into a home's decor. A variety of sizes permits installation in many situations.

Culture

An initial investment of $ 1,000 for this type of set-up is realistic. These lights operate on 110 current and should be on their own circuit. Anyone lacking electrical expertise is encouraged to hire an electrician to make the necessary modifications. It is easy to determine the impact operating these lights will have on your electric bill. One thousand watts is equal to one kilowatt. Electric bills are calculated in kilowatt hours. Therefore, a 1000-watt bulb that burns for 12 hours per day will add 12 kilowatt hours per day to the bill. A 400-watt fixture will use 5.6 kilowatt hours.

My primary growing environment consists of a 10 x 18 foot portion of a converted garage that includes a 1000-watt metal-halide unit on a 6-foot light mover set end-to-end with a 400-watt high-pressure sodium unit on a 6-foot light mover. Plants in containers are positioned on benches; those on plaques are suspended from wire mesh attached to the wall. The majority are in slatted baskets suspended from chains near the ceiling. A stationary 250-watt metal-halide light and a four-tier light cart with fluorescent lights supplement the HID lighting. About 1,000 orchids are in this area.

The room is illuminated the same number of hours as outdoors. This ranges from 11 hours in the winter to 18 hours in the summer. Every two weeks, the timer is adjusted at 15-minute increments.

For anyone on a budget, or with a smaller area to illuminate, there are kits available through dealers that take the guesswork out of assembling a HID light garden. Some are in attractive cases and finishes that blend into a home's decor. A variety of sizes permits installation in many situations.

Thoroughly research the needs of plants to be grown. Make sure the growing area is capable of meeting their specific requirements on a continuing basis. Under HID-lighting conditions, plants require watering more frequently than those cultivated beneath fluorescent lights. A significant decrease in humidity is noticeable. The minimum-maximum thermometer will monitor temperature patterns and indicate if any supplemental heating or cooling is necessary.

In my growing area, no heating or cooling is required. There is always a 15 to 20 degree differential between day and night temperature caused by the heat generated by the HID lights and ballasts. Ventilation is provided by opening a skylight and/or a patio door when needed and three wall-mounted fans that operate continuously.

Figure 6. The intensity of light decreases as it travels from the source.

To reduce maintenance, I designed an automated misting/watering system with a Dos-a-matic fertilizer proportioner that will operate one week at a time completely unattended. To compensate for the hot lights, water is applied three to six times each day beginning at 6 am. This might sound like the plants are being overwatered, but they are not; the excess moisture evaporates quickly. The misters turn on for two minutes every 60 to 90 minutes and drench the plants with a heavy mist. No water is applied after 1 or 1:30 pm to guarantee the plants are dry by night. Dyna-Gro 7-7-7 and Mag-pro combined in a weak solution are applied with every watering. A five-gallon pre-mix lasts one week. Then I water without fertilizer for two days to leach out accumulated salts. It is important that homeowners adjust the watering schedule to reflect the peculiarities of their environment, plants and potting media.

Due to an uncontrollably heavy hand when watering, I grow my orchids primarily mounted on cork bark, tree-fern slabs or in slatted baskets. No medium is placed around the roots of vandas in baskets; chunks of tree fern and cork buffer the roots of miltoniopsis, phalaenopsis and cattleyas.

Humidity is maintained by a direct-plumbed Herrmidifier 500 humidifier that is controlled by a humidistat set at 70 percent.

Summer Care

From late April or early May through October, most of the orchids are set on a deck or under trees in my front yard. Many are moved directly to their summer quarters, except for the vandas and dendrobiums destined for direct sun. These are moved to their new locales in three stages over one week to adjust their foliage to the increased light levels. Some warm-growing species and other plants that have shown an aversion to the cool and damp conditions occasionally encountered outdoors remain indoors year round.

Before returning the plants indoors, each one is sprayed with Sunspray, a light-grade horticultural oil.

When an orchid collection has consumed all available space, investigate the possibilities of growing these plants under HID lights, especially if dendrobiums and vandas are among your favorites.

Orchids to Try

Kenneth M. Rossman is a real-estate appraiser. He has been growing houseplants for 15 years, during five of which he has been cultivating orchids under lights. Joyce, Ken's wife, now frisks him and searches the car for contraband orchids after meetings and shows. 92 Harbour Lane, Bay Shore, New York 11706.