I think I am going to try it. I have a phal and oncidium in mind this might work on (the oncidium has just about finished its new growth that it was working on when I bought it).

I have a few more questions that hopefully someone could help me on:
1) Does there have to be sand/rocks in between the two pots or can I fill it with just water?
2) Will the plant(s) I choose have to be covered with anything to maximize cooling? (I'm asking because I'm not sure if a smaller scale zeer can cool as much as a big one).
3) For this to initiate a spike, I should fill it at night and empty it in morning, right?

1 If you fill the space with water, it will leak back into your inner pot through the drain hole. You probably don't want to grow it as an aquatic plant, though some people do grow some orchids in water. You could grow the orchid in an inner pot with no holes, but that isn't a good idea most of the time. Sand, not rocks, is what you want between the pots, because sand doesn't move when settled, and it wicks water better than larger particles.

2 The cooling comes from water evaporating from the outer clay pot. The roots are cooled. Cooling will be proportional to the surface area of the outer pot. The larger the outer pot the greater the cooling effect. Evaporative cooling only works when the dew point is below 55 degrees F / 13C. If you look at your local weather on weather.gov you can find the current dew point. In El Centro your humidity is almost always very low, so the dew point will almost always be below 55 degrees F.

Most orchids don't do well enclosed under a bag or jar when their roots are wet, so don't do that.

3 If you are going to use this method to cool your plants, the sand between the pots should be moist all the time. You need to use very pure water for this technique or salts from the water will quickly build up outside the outer pot and inside the inner pot, and potentially burn roots.

If you use 2 nested clay pots with sand in between, the moisture in the sand will also wick back into your orchid root ball. Water conducts heat quite well, so this would lead to the best cooling. If I used this technique I would be sure my plants were in a very well-aerated mix, such as very large bark. Fine mixes might stay too wet with too little air.

If your orchid is in a plastic pot nested in a clay pot, the cooling will still take place on the surface, but less water will wick from the sand into your orchid, since it will only go through the drain holes. Plastic does conduct heat but not nearly so well as wet fired clay.

Or you could grow semi-hydroponic with a single clay pot standing in a dish of water and LECA as growing medium, and get a similar effect. The water would wick up the clay pot and evaporate, cooling it. There is a large semi-hydroponic forum here on the Orchid Board. Most people who use this method (including me) use plastic containers because that is how the method was first described, and we aren't aiming at cooling. But after reading this thread, I think I'm going to try clay pot S/H for something that needs cooler temperatures and see how that goes.

Thank you Estación, I'm starting to understanding how the evaporative cooling works. I didn't even think about the salt buildup. I'll have to use my drinking water that comes from those water machines. I'd also seal the holes in the pots with aquarium sealant (I have fish tanks and used to create caves with it). I have a few more questions though that I'm hoping you might be willing to answer?

If I set the clear pot inside the middle they're not going to cool the same as if they were actually planted in the middle pot, right? Do you think it could cool enough to trigger a spike? My thermometer on the pant stand is normally 84°F during day and 77°F at night. I would remove the clear pot during day and place it back inside the pot night to try and get the biggest temp difference.

Could I use a bare root phal? I have two growing bare root. The larger one is in a clay pot and a couple roots are starting to wrap around the inside of the pot. Would this cool the same as if it were planted inside media touching the inner clay pot? Or would it at least cool better than a clear pot inside the center?

I know a lot of people use S/H with great success but I'm still weary. I wished the pellets were sold in stores here, then I'd probably buy some already. For now I just want to trigger a spike on a phal or onc. :)

Picture of the zeer
 

I thought I would post a picture of my zeer which has been in use for about 3 years:

Attachment 116174

You can see that the space between pots is filled with sand. The plant is actually potted in a black net pot, lined with U.S.-grown sphagnum, Inside the lining is a mix of bark, charcoal and about 10% sphagnum. Coelogyne cristata likes a fairly damp mix. The zeer keeps the roots both cool and moist. For plants needing drier roots, I would consider a larger gap between the zeer and the pot the plant grows in.

Thanks Orchid Whisperer! That's a beautiful example you have there. I'm finally getting how the moisture travels so now I know why I need the gap. I picked out which phal I'm going to use today. Now I need to go to the store and buy a couple terra cotta pots. I'm really excited to see if this will work or not. :)

Those roots in the pictures with the earthworm don't look bad at all and the bulbs are nice and green.
Just repot it, stake it so it does not wiggle and it should grow.

For a Phalaenopsis, if your goal is a temperature drop for spike initiation, it is probably easier to leave the plant where the temperature drops 10 - 15 F relative to whatever your summer high temperature was (but try not to go lower than 50 F).

If you do try the zeer for this purpose, let us know how it works out!

I know it would, but the temperature hasn't dropped enough here. The house doesn't get under 78F, by the windows its warmer. In winter I open the window by the orchids which'll let them get cool air. Otherwise they'd have to go outside, which might be to harsh for them. My backayrd is 100% dirt and the front yard has a little porch. This summer alone I killed 8 bushes, 5 haworthia, 4 kalanchoes, 1 lemon tree and a gardenia. I don't want my outdoor, black thumb of death to kill my orchids too... :_(

Since I've never rebloomed an orchid, you gave me the idea to try an indoor experiment until I give up all hope and just wait for winter to get here. :)