Humidity is often one of the hardest requirements for hobby growers to provide on the windowsill – and yet it is such a vital ingredient to successful orchid cultivation. The average relative humidity (RH), how much moisture the air contains, in most homes rarely rises above 30%. In the winter with heaters on it can be even less. At locations where most orchids thrive humidity levels often reach 80-100%, but an average of between 50-70% will suffice for most orchids in cultivation. One very important point to remember, the higher the RH the better air circulation you need or the stagnant air will promote mold or diseases. There are many methods that try to elevate the humidity around the plants, but few are very effective. Grouping plants close together helps a little bit, adding humidity trays helps a little more (but hardly enough to be worth the effort in my opinion). Misting does very little for raising the RH for any marked amount of time. If you want results raising humidity, you really need to consider a humidifier. You run the humidifier at night when the plants best benefits from the added humidity.


Cold air humidifiers

This is what I would recommend for orchid purposes. Cold air systems are cheaper to run and cover a larger area than hot-air models. They are self-regulating which means that less evaporation occur when the air is already very damp. They also help to cool the air while supplying it with moisture.
Maintaining the humidifier is very important. The filters must be replaced and it must be cleaned frequently to make sure no dangerous mold or bacteria collects, which is then dispersed into the air we breathe. I clean mine once a month with a weak bleach solution or vinegar. I let it soak for about 20 minutes and then wash it out thoroughly.

Since cold air humidifiers will not sterilize the water you have to use reverse osmosis (R/O) or distilled water. (If you do not have an R/O filter you can use the condense water collected by the clothes dryer.) Regular tap water contains tiny microorganisms and minerals and the humidifier will disperse these into the air in form of a fine white dust that can clog the pores of the plants – and it is nothing I recommend you breathe either.

The three most common cold air humidifiers are

Evaporation (or wick)

The easiest system to run, consisting of a water tank, wick and fan. The wick absorbs water and the fan blows air onto the wick, the water evaporates and the humid air is blown out into the room, raising the humidity.


Pros: fairly inexpensive to buy and easy to operate
Cons: loud when running, moderately efficient


Impeller driven

About the same idea as the evaporation model above, but with a spinning disc or propeller that is breaking the water droplets into tiny droplets which creates a fine mist. You can actually see the mist when it comes out of the machine and it usually runs a little quieter than the evaporation models.


Pros: fairly inexpensive to buy and easy to operate
Cons: loud when running, moderately efficient



This system use ultrasonic sound waves to vibrate the water converting it into a cold fog that you can see.


Pros: easy to run, very effective, silent running, very efficient – well worth every penny in my opinion!
Cons: a bit more expensive


Warm air humidifiers

I do not really think these are suitable for orchid growing. Since they use a heating element to heat the water they use a lot of electricity so they are more expensive to run. The vapor also tends to stay pretty close to the unit and its benefits do not spread over a larger area – making them pretty ineffective in my opinion. The good thing about these hot air models is that by boiling the water first, mold or bacteria is killed and the minerals found in the water is removed before being discharged into the air.


My growing areas

*A lot has happened the past two years… things that has had major consequences on my growing areas. This page will be updated very soon to reflect this. 

The growing room

At first I chose an inexpensive cold air impeller driven humidifier, but thankfully that one broke down after about 9 months. I say thankfully because it was not very effective and it was very loud to run- Luckily I got to replace in under warranty. I replaced it with a 5L capacity ultrasonic cold air humidifier instead (Honeywell HH200E4). That one lasted about 6 months, and I have run through three of those now (luckily under warranty)… they just do not last. Last time they replaced it with a “Wilfa HU-6″ ultrasonic humidifier (still under warranty). We’ll see how long that one lasts…

Since the cool fog kind of blows out of the nozzle then immediately fall I needed a rig to bring the flow further up in my growing window then have it gently fall down on the 3 levels of orchids below so I get better coverage and at the same time raising the over all RH in the room. But I do not wish to keep the 5L water container for the humidifier 3 meters up in the air, so I built a chimney using regular PVC pipes and a cheap funnel. Three holes drilled in the pipe running across the top and the fog flows down the top like magic..! Read about the installation here.

In my small growing room, with the door closed, I get about 70% humidity at night. I keep it on a timer running the unit every other half hour for a half hour at a time every night – and once again at noon for good measure.


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Intermediate vivariums

In the intermediate vivariums I used to have 3 humidity trays on the bottom filled with water to help raise the humidity. But after filling the space with orchids I do not have to keep the humidity trays anymore, they serve as collection trays instead. Thanks to the amount of plants and the humid growing media, humidity stays fairly constant. But I run a small ultrasonic humidifier for about 15 minutes twice a day to help maintain a good level. I use the same humidifier for both of the intermediate vivariums, splitting the fog in two with the help of a rubber hose and some duct tape. Simple but effective. A temperature and hygrometer tells me all is working like it should. I spent about $15 on one that is showing both humidity and temperature, plus save the high/low value so that you can keep track of the measurements.

PS! See all those hard water stains I used to get on the vivarium glass? A pain in the, well, you know what. This was fixed when I finally got a reverse osmosis filter. The filtered water does stain the glass in this way. A very nice added benefit.


Intermediate vivariumVivariumIntermediate vivariumIntermediate vivarium


Cool vivarium

In the cool vivarium I use a “Wilfa HU-6″ ultrasonic humidifier with an option for either hot or cold steam (I will run it cold of course) with a capacity of up to 300 ml/hour and the water tank holds 6 liters. I use PVC pipes to make another “chimney” for the fog so I kan keep the unit on the outsde. I pipe it into the viv. through a hole in the side. I control the RH with a Lucky Reptile Humidity Control II humidistat, the same brand and concept as my thermostat, with two circuits making it possible to have different settings for day and night. I set mine for 75% during the day and 85% at night with a 5% differential, which means that the humidifier will start up as soon as the measured humidity drops 5% below the desired setting. A temperature and hygrometer tells me all is working like it should.


Orchid cool vivarium - fog systemFog updateOrchid cool vivarium - fog system installationOrchid cool vivarium - fogger