Overhead Mist System

Hi Zach. Unless your system is one of the high end, air-compressor-powered sort that produces super-fine mist, overhead misting for orchids can be fraught with dangers. Most orchid growers I know only use beneath-bench systems.

If you must use overhead misting, add on a regular timer to your cycle timer so that the cycle timer is only activated during the hours of the day that are warm enough for the water to evaporate quickly. Unless one is outdoors in the breezy tropics (or cloud forest), it's important to think of providing ambient humidity and actual water contact with one's plants as entirely separate.

As for how often to run your cycles, this is something that is best figured out as you go. I use misters on a cycle timer in my warm grow chamber and I find that at different times of year (varying day length, night temperatures, frequency of swamp cooling, etc.) change the equation every 2 months or so. The most important thing is making sure that your plants don't get wet from the misters. If they do get wet, you must make sure they can dry off properly before getting wet again. Having a hygrometer (or a couple) is essential to gauge the effectiveness of your misting schedule.

I can't speak to cooling with misters, but perhaps someone else can

 

And my only (potentially) worthwhile input is this: I completely replaced my overhead mister system with an under-bench system mere months after installing the overhead system. Wet is bad, and that is what I got with the overhead system. My system was only operating on about 100 psi so I didn't get fog - I got mist - which was the problem - there's a huge difference. My situation may be different than yours - I maintain a very warm house - but watch those overhead systems very carefully. I think air movement will have to be carefully coordinated with overhead water, and air movememnt is something that's rather rigid in my situation. Best of luck!

 

Zach, I installed an overhead mist system in my shadehouse a year ago. http://www.orchidsinteractive.com/showthread.php?t=6446&highlight=mist Unfortunately, I can't really speak to its long-term effectiveness yet because the darn thing has had many problems causing significant downtime. I do think it is up and running strong now. Mine is a 1000psi system, which comes close to creating a fog in my humid conditions, but it's still a little wetter than I'd like. So far, my multiple fans have done a nice job of reducing that moisture.

The system does reduce the temperatures, and it makes it much more pleasant to be in the shadehouse in the heat of the summer. I'd strongly recommed putting the system on a thermostat, instead of a timer, though! I have mine set to come on at 90°F, so it only runs during the heat of the day. The plants are nice and dry by bedtime, and I don't have to worry about them getting wet overnight; or in the cooler, very humid mornings.

Good luck!

 

I'm going to agree with everyone else. An overhead system is going to cause more problems than it's worth in your situation. Alexis can get away with it because of droplet size and the fact she's growing in a shadehouse. The (relative) lack of fresh air is going to cause issues with evaporation for you. Marni is an incredible grower, and she consistently advocates using below-bench cooling/humidification systems. Like Jacob mentions, there's a huge difference between humidity and wet plants.

 

I have an over head mist system, but it is over a walkway and not directly on the plants. I still get mist drifting on top of plants which causes some nasty calcium deposits. Even with a filter. We get some horrendously hot days here in the Sacramento area, so the overhead misters add that few degrees of cooling I need. But, I do have to watch the plants in the general area for too wet conditions and move them.

 

T. Migratoris has a good point... define your misting regimine based on conditions and not time. Unless it's your sole source of watering. Then do both.

 

I guess I don't understand this reply. You're going to leave things the way they are after everyone suggested you don't?

 

LOL!

 

Are all of your plants mounted or in baskets? If so, affix the misters on the walls down low so the floor is sprayed.

 

No. It's actually going to dry everything out because the humidity will act like a sponge and suck all of the moisture from the air above. It's going to create a desert-like environment above the misters. The high-humidity down low induces a process known as rheohydrolization that, somewhat perversly, transfers humidity from the warmer air above to the cooler air near the floor, thus creating a vacuum of sorts on the humidity in the warmer region. So, your floor area is going to be swampy while your areas above are going to be crisp and dry.

 

Jon, I'm sorry, but I have a very hard time accepting that, for a number of reasons.

1) You are forcing water into the air, and assuming sufficiently small droplets, that local volume of air will be saturated, meaning it cannot possibly absorb more.

2) That "rheohydrolyzation" process is in direct opposition to the fact that the laws of nature absolutely abhors gradients. If the air in one location has more moisture dissolved in it than in another, the natural tendency will be to spread it to a uniform concentration throughout the contained volume.

3) Add to that the fact that the warmer air in the upper reaches can hold more moisture to begin with, and it will try to draw moisture from below into the less dense strata.

4) Having fans running will mix the air thoroughly, accelerating the distribution of the dissolve moisture (humidity).

Maybe I'm wrong, but concerning "rheohydrolyzation", Google cannot find any reference to that - can you point me to something so I can learn about it?

An afterthought: if "rheohydrolyzation" is a fact - or maybe I should say "applicable" - then humidity trays would be wonderfully effective, as that very thin layer of local humidity concentration would draw in moisture from the rest of the house and the plants would love it....and we know that doesn't happen, because if it did, they'd never have to be refilled!

 

LOL Ray. Here's your sign.....

 

Oh man.