As is the “norm” for today’s internet-spread information, many have misinterpreted and shared incorrect advice about the need for air movement around orchids. Let me offer some clarity.
First, let’s ask ourselves, “what is that air movement for? What’s it supposed to do?”
The primary answer is that air movement prevents pockets of damp, stagnant air forming around the plants, which can quickly become incubators for pathogenic bacteria and fungi. Secondly, it can aid in drying the plants off after watering, also eliminating breeding grounds for pathogens.
OK. That makes sense, so let’s now ask ourselves, “do we have pockets of stagnant air around our plants”, and “do they need help drying?”
If you grow within your home, the answer is “probably not’, as they are likely eliminated by your HVAC system, the opening and closing of doors, movement by people and pets, and convection currents caused by the cooling of the air near windows. Plus, with air-conditioned summer-, and heated winter environments, the home is usually dry enough that pockets of moisture don’t hang around for long.
Now then, if you grow in an enclosed environment, such as a terrarium, Wardian Case or greenhouse, that could be – and likely is – entirely different. A greenhouse, being a structure specifically designed to hold onto humidity and warmth, can really benefit from gentle, tumbling air to prevent stratification and stagnation. That is often accomplished by placing several horizontal air flow (HAF) fans in opposite corners blowing down the length of the structure to created a constant circulation of air.
If the structure is large enough, it may be beneficial to use ceiling fans or “turbulators”, instead.
Turbulator fans (on right) are particularly good in greenhouses, as tend to create constantly-varying, vertically tumbling pockets of air, rather than a breeze.
When it comes to indoor enclosures, the use of small fans to keep air circulating is almost a “must”. In grow tents and tightly-closed terrariums and paludariums, keeping the air moving is often done using small axial or “muffin” fans.
Such low-volume fans should be used to circulate the air within the enclosure, leaving a small opening for fresh air exchange. If fans are used to force that exchange with outside air, keeping a reasonable humidity level with be difficult.
Sometimes, however, even small enclosures don’t require fans. I have a glass cylinder enclosure on my desk for a couple of mounted mini-orchids. The top is closed with a piece of plexiglas, leaving a crescent-shaped opening that is only 1/4″ at it’s largest. That is the entire ventilation for the enclosure, and plants in it still dry within an hour of being watered.