Growing Plants Indoors by Mark Robbins

(From presentation to Maryland Orchid Society in June 2001)

Overview. You can grow and bloom any type of orchid in your house. However, houses were designed for your comfort and not for that of orchids. Creating places with an environment that orchids will like, or at least tolerate, can be easy or hard depending on the particular plant. You have to decide how hard you want to work when choosing plants.

Some plants that like conditions that are typical in the home are phalaenopsis and doritaenopsis, many pahiopedilums (especially Maudiae-type, concolor, niveum and some brachypetalum hybrids), miniature and compact cattleyas, and compact dendrobiums. I find the biggest limitations are temperature and plant size.

The American Orchid Society provides culture sheets for most types of orchids and they can be found at the web sites listed below. These give general guidelines for the temperature range, and the amount of light, water, fertilizer, and humidity that different plants need. Most orchids will tolerate a wide range of conditions and there are large variations within a given species or hybrid. Brief notes on how to provide plant needs in a home follow. Many people give their plants a summer vacation outdoors, but I haven't found that necessary.

Light. The simplest choice is a window. Plants have adapted to the sun's spectrum of light frequencies and sun is free. The problem is that the light is difficult to regulate and highly variable. Culture sheets generally suggest an East or South window for low or high light plants, respectively. Keep in mind that much more than the direction of the window is important. A window that works well in winter may be shaded by leaves in the summer, or a nearby building may block the lower winter sun. Dirty windows can block a lot of light and screens can block 1/4 to 1/2 of the light. I've had leaves burn when I took the screens off in the winter. The distance from the window is also very important. Moving a plant 6 to 12 inches back from a window can keep it from burning or keep it from blooming.

How does one tell where to put a plant? In many cases you will have other houseplants to guide you. Phalaenopsis and paphiopedilums are often happy where African violets grow well. Light meters can also help, but the light intensity varies greatly over the course of the day and year. The best guide is to watch the leaves of the plant. Move the plant to a darker place if you see leaf burn or bleaching of the leaves. Move the plant to a brighter spot if the leaves are too dark a green or the plant doesn't grow and flower well. This can be frustrating because some changes take months to establish. Having several plants at different locations can speed things up.

The simplest alternative, or supplement, to windows is fluorescent lighting. Most orchids that are commonly cultivated can get enough light to grow and flower under 4 foot fluorescent lights. Shorter lights are available, but are much less efficient. Eight foot lamps are harder to work with and not much more efficient. Putting four tubes side-by-side creates bright uniform lighting over a 2' by 4' area. One of the best things is the lack of shadows - almost every leaf gets light from somewhere. I grow cattleyas with the top of their leaves between 2 and 6" from the tubes and paphiopedilums and phalaenopsis at 4 to 10" from the tubes. The distance is not as important as some books say when you have several tubes side-by-side. I vary the day length from 11 or 12 hours in the winter to 14 in the summer on most lights. However, my phalaenopsis have a steady 12 hours all year and don't seem to mind. Some plants are reported to need a long dark night, but I haven't found this to be common. This might become an issue if the lights were on more than 14 hours a day. Some growers recommend 16 hours.

Not all fluorescent fixtures or tubes are the same. I have found that cheap shop lights and fixtures wear out quickly. I also get more light from the same bulb in a slightly more expensive fixture. EB Flourescent, a local fixture company, says that most shop lights have a 30W balance rather than a true 40W. My light meter sees a variation from over 5000 at the tube to 3000 to 3500 with cheap shop lights. People grow successfully with all types of bulbs. I have been happy with Wide Spectrum Grow-Lux, which are not that expensive when bought by the dozen. You will frequently see statements that fluorescent tubes need to be replaced once a year. I have measured the intensity and see no evidence for this. However, bulbs that are two or more years old are noticeably dimmer at the ends. Cheaper fixtures cause bulbs to wear out more quickly.

The next step up is high-intensity-discharge (HID) lighting. There is a 150W bulb ($50) that is fairly easy to install, but having light come from a single point leads to lots of shadowing. This bulb is probably best for small areas or to supplement a window. Larger lamps need a special ballast and are much more expensive (~$300). However, they are much more efficient, and the bulb replacement cost is not much more. The metal-halide lights are closest to sunlight and said to be best when there is no other lighting. High-pressure sodium lights are more efficient and good for blooming, but have less energy at the frequencies needed for growth.

I found that a single stationary HID light gave uneven lighting. I would recommend spreading the light with a light track or mover, or mounting several lamps in a line. I grow plants 18 to 36 inches from my 400W metal-halide on a 4-foot long light track. I put high light plants in the center and low light plants at the edges. The day length is the same as for fluorescents. These bulbs dim by 1/3 after a year and should be replaced annually. I have recently concluded that my 4’x6’ growing area is too big for one 400W bulb and plan to use two side by side.

Whatever the light source, you can use white paint or reflective mylar to direct more of it on to your plants. Mylar is more reflective, but the light bounces off like a mirror. Paint spreads the light in many directions. Bob Travers has found that utility companies give a better rate if you use power at off-peak hours. The company puts in a meter that determines when power is used and charges according to the time. By keeping the lights on at night while he is home, Bob saves substantially on his bill.

Water and Fertilizer. The basic requirements for water and fertilizer don't change when you grow plants indoors. However, the rate at which plants dry out depends greatly on humidity, air movement, temperature and other factors. You will have to water at a different frequency than a greenhouse grower, and change the frequency with the environment around the plant.

One of the biggest challenges is getting water into pots without damaging your house or spending all day watering. A small number of plants can be carried to the sink and placed under the faucet. This is easier if one has perforated trays inside watertight trays. The perforated tray can then be lifted out and placed in the shower for watering, and then back in the watertight tray for transport back to the growing area. A larger number can be placed over watertight trays that hold the runoff below the pots. Evaporation from the trays (and nearby plants) helps maintain humidity around the plants. With luck the water will evaporate fast enough that the trays don't need to be emptied. They may need to be siphoned dry from time to time. I find this approach works best for promix ("mud") and sphagnum because I get less runoff than for bark. I water with a pressure sprayer. This takes a little longer, but limits the runoff. A little spilled water is less serious in my basement setup. I water with a wand attached to a hose and let the runoff go into a reservoir. When the reservoir gets full I empty it with a sump pump.

Temperature. Temperature can be hard to control. My plants get very hot in the summer because they aren't air-conditioned. Some sensitive plants summer in my office. My plants also don't get very cold nights in winter (the other residents of the house complained). Cymbidiums and some of the most beautiful miltoniopsis and related intergeneric crosses either won't bloom or won't bloom with the desirable deep colors if they don't get cold nights. If you have a sun porch or other area that gets cold at night you may have more luck with these. You may also find a drafty window or pantry that works well.

Humidity. In the winter a house may drop below the minimum 50% humidity recommended for most orchids. My skin has similar tastes as the orchids and I try to keep the humidity up around 50% with a humidifier. My basement doesn't have a humidifier and may get down to 30% in the winter. The plants seem to survive this, perhaps because the local humidity is higher due to evaporation from the potting media, trays and nearby plants. I have not found that misting plants is needed.

In the summer the humidity and temperatures may get much higher than recommended. In general, plants tolerate higher humidity at low temperatures and vice versa. I aim for lots of air movement in the summer. I used to use box fans, but have switched to 16” and larger rotating fans. Air movement helps to limit heat buildup in the summer and limits bacterial and fungal infection in the winter. I think it also helps the potting mix to dry out more evenly.

Potting Media. Because my growing conditions are dryer and warmer than most greenhouses I find that some plants need, or can tolerate, a more absorbent mix. I try to make the mix less absorbent as the pot size increases so that plants dry out at more comparable rates. I find anything grows in sphagnum and it is easy to look at the surface and know it is time to water. Phalaenopsis and phragmipediums seem to do well in promix, which changes color when it's time to water. I sometimes use clear plastic pots so I can see when some plants need water. I judge others by the weight. To make this easy I avoid heavy clay pots and mixes with too much charcoal or lava rock.

I don't water on a schedule, but mark a calendar or special sheet to keep track of when I watered which plant. This helps me focus on the plants that are likely to need water and helps keep me from forgetting to water plants. Plants are grouped by drying time and water requirements. While this makes life simpler, plants do better when each is watered at its own time.

Suppliers for indoor growing that I've found reliable:

IGS 734-426-9080 (www.indoorgardensupplies.com) igsmi@aol.com. Full line of lights, stand, fixtures, etc.

Hydrofarm East 800-227-4567 (www.hydrofarm.com) High Intensity light setups and info

Charley's Greenhouse Supply 800-233-3078, More for greenhouse growers, but some useful supplies

IPM Laboratories, Inc. 315-497-2063 (www.ipmlabs.com). Mite and other predators for controlling pests

The Orchid Mall: http://www.orchidmall.com/index.htm

Antec Laboratory (www.ladyslipper.com) for paph info.

The Maryland Orchid Society page has links to some sites: http://www.pha.jhu.edu/~mr/mos.html