Greenhouse Orchid Care

General Information

There are many types of greenhouses out there, ranging from the humble tent and hoop greenhouses to the professional structures with automation.  Greenhouses may or may not contain supplemental lighting, but they all contain fans, a heating/cooling system, and some way to water the plants.  In general, greenhouses are muggy environments, and require a lot of energy to run.  You may be able to grow certain orchids in a greenhouse better than indoors, but there are some orchids that will never do well in a greenhouse, because of the heat – you can (and should) grow all your cool-loving orchids indoors instead.

Some greenhouses are free-standing structures, and others are partially buried underground.  Some shipping containers have been converted to being greenhouses that are run entirely off of artificial lights.  They moreso fall under indoor growing conditions because the climate is so stable.  Greenhouses require stricter sanitation methods than indoor growing because they are wet, warm environments – perfect for pests and fungi in which to wildly spread.

Greenhouses also have a problem with temperature management – especially in southern latitudes, and in northern latitudes in the summer.  Many greenhouses use a combination of fans and a water-cooling system (kind of like a swamp cooler) to cool their greenhouses.  It also helps to use shade cloth if greenhouses are having a heating problem, as well as even opening up the roof of the greenhouse entirely during the summer!

Additionally, it’s helpful to know the angle of the sun in the sky and the duration of daylength.  You can generate a solar chart for your exact location on Earth by visiting the University of Oregon’s Solar Radiation Monitoring Laboratory.

Whatever the size, similar suggestions for selection, design and installation apply. There are three major types of greenhouses to consider. The lean-to greenhouse is usually small, about 6 to 10 feet long. One of its long sides is formed by the side of the house to which it is attached. Relatively inexpensive to make and maintain, its major drawbacks are a lack of space for an expanding collection and a tendency to heat up and cool off more rapidly than is desirable.

The attached greenhouse is an extension of one's home, connected at the narrow end rather than the long side, as with the lean-to greenhouse. It is generally large and thus capable of providing more reasonable control over humidity, ventilation and expansion problems. Some homeowners incorporate a living area into a lean-to or attached greenhouse.

The free-standing greenhouse is unattached on all four sides. It is the most expensive to construct but, aside from some inconvenience of access in inclement weather, it offers maximum light and the best control. Some space must be sacrificed for a work bench and storage area.

Visit as many orchid greenhouses as possible, and consult books on and manufacturers of greenhouses before making a final decision. Where space is limited inside the home, window greenhouses offer a prime space in which to cultivate small-growing orchids. Opt for a model with vents and small fans that enhance ventilation. Two or three shelves increase space; they may be solid, to prevent water from dripping on the plants below, or perforated to aid air circulation.

The optimum size with which to begin is a greenhouse 14 feet wide and 14 to 20 feet long. This affords a center bench as well as two side benches. Such a greenhouse may seem enormous at first, and unnecessary for an initial collection, but there are several factors to consider. First, those contemplating a greenhouse are serious about orchid growing. Consequently, the collection will inevitably grow by leaps and bounds. What seems to be adequate space today will become a major limitation in two years. Second, since a large greenhouse is preferable in the long run, it is less expensive to build it now than to add an extension onto a smaller one in the future.

Greenhouse procedures

Cleanliness is next to godliness.  Picking off dead leaves and removing old dead sheaths is essential to limiting areas where pests and fungi can hide and breed.  Regularly cleaning the benches and greenhouse floors with either a fungicide (like Physan) or 10% bleach is essential to keeping the water molds (fast killer of orchids) at bay.  Create an Integrated Pest Management (IPM) program where you either spray insecticide regularly, or cultivate plants that house beneficial insects.  You can combine some beneficial insects with treatments of systemic pesticides, if you so wish for greenhouses to get maximum as-organic-as-possible pest management.  Consult your local agricultural extension for more details on IPM plans, beneficial insects, and local growing conditions.

Take the following information as general guidelines, not biblical commandments.  In general, follow the following guidelines, and your plants will be set off on a good start:

  • Greenhouses end up with being too hot, especially during the summer and at lower latitudes.  Ensure that you have an adequate cooling system, use shade cloth, and if possible, create a temporary wall to shade and block out the sun for a part of the day, if your greenhouse is too exposed.
  • Proper sanitation and regular cleaning will save you weeks of headaches down the road.  Remove dead leaves and sheaths to remove places where fungi and pests can hide and breed.
  • Slime molds and wet rots can splash back up from the floor, and make a home in concrete or the soil readily.  Keep the floors well-swept, and once a month, bleach the floors or spray down with Physan/a fungicide.
  • You will water daily, or nearly daily.
  • Orchids that need a temperature swing over time to bloom will do particularly well.
  • Because of the humidity and the daily waterings, you will need to switch to coarser media – the coarser, the better for most plants.
  • Thin-rooted orchids tend to do well in finer, non-sphagnum media.
  • In general, in a greenhouse, you do not need to use much sphagnum in your mixes as you do inside.


The foundation of a greenhouse is an additional but necessary expense. All greenhouses should have one. In areas where temperatures dip below 35 F, the foundation, whether of poured concrete, brick or cinder, must extend well below the frost line. Otherwise, the greenhouse will warp and twist. The floor is always the leveled earth, never a slab of concrete, thus ensuring proper drainage. A clay-earth floor may be covered with several inches of cinders or gravel.


Construct the height and width of benches for convenience, generally 30 inches tall and 33 inches wide. The center bench may be twice this width as it is accessible from two sides. Select treated lumber that is resistant to moisture, or aluminum and steel, which have proven more durable, even though initially they are more expensive. The top surface of the benches should provide aeration and so should be formed either by redwood or cypress strips, spaced about their own width apart, or by a strong aluminum mesh. Air can thus circulate upward through the pots.


A heating system is essential in any area that has recorded temperatures below 45 F. It is wise to provide an emergency heater as well. Too many collections have been lost to freezing due to oversights, power failures or lack of proper maintenance of the heating system. A wide choice of heating systems is available: steam, circulating hot water, ducted hot air, natural gas. Where bottled gas must be used, absolutely no fumes should penetrate into the greenhouse. Orchids are notoriously susceptible to ethylene gas and will soon die if any is present.

Cooling and Ventilation

Except in very warm climates, a cooling system is usually not essential, because manual ventilation is adequate for those extra warm days. To grow odontoglossums and similar cool-growing genera, it may be advantageous, even necessary, to invest in an evaporative cooler in order to provide the low temperatures these orchids require. Automatic humidifying devices are necessary and should run in conjunction with adequate ventilation mechanisms. Side and roof vents operated automatically or manually, in addition to several fans running continuously, will keep the moisture-laden air moving freely throughout the greenhouse. Shading will depend largely on the characteristics of the particular climate and will have to be adjusted accordingly.

Additional Information