Gravel at bottom of pot

[Ray]

[Leafmite]

Interesting. I never noticed much of a difference between potting with gravel and not using gravel. The dirt tends to settle between the gravel anyway and so it really is kind of a moot point unless you are growing a plant that prefers rocky soil. The big rose companies still recommend adding rocks or pot shards to the bottom of the pot before planting a rose in a container but I am not going to be doing that when I get my roses.

I did get the idea to use lava rock as a medium for the orchids from this idea of drainage, though, so there was a benefit.

As for the soil leaking from the pot, that has never been much of a problem, either. I always put a saucer under the pot and there is never much dirt in the saucer. If the hole in the pot is very large, a coffee filter or a sheet of newspaper cut to fit the bottom will prevent the dirt/medium from exiting.

[lobotomizedgoat]

If you're concerned about moisture retention another option could be to add holes to the pot for ventilation. I used a $10 diamond hole saw bit with a basic electric hand drill to add holes to the sides of ceramic pots for a couple of my orchids.

[MateoinLosAngeles]

As many have pointed out, when you reduce the height of the water holding media (absorption and/or bridging) you increase the amount of water retained and lower the amount of space available for gas exchange, thus increasing the odds of the roots asphyxiating in their own gases and dying.

A quick rule of thumb is taller pots allow for better air flow.

One drainage hole is fine, if it's terracotta it's more than fine since the pot will also absorb water and facilitate air exchange (careful with it getting too cold with tropical plants), if it's a glazed pot then I think the choice of medium AND the watering technique will have an effect (glazed will retain more water and moisture for longer).

If you're using fairly uniform media, like Orchiata bark, that holds on to their shape and doesn't become mush then you're good to go. If you're using Sphagnum moss the paradoxical solution is to actually pack it more and water from below using the tray method for the moss to absorb moisture without the weight of the water affecting its structure. I don't think you will need bottom rockery under any condition.

Keep in mind Roberta's advice about choose the pot vs. saving the roots. I have many plants that are completely attachade to their baskets, in those cases I drill a hole for the medium to fall off and up-pot the basket into a bigger basket, then fill with fresh media. If I use a terracotta pot, I give it a good whack and up-pot the plant with any pieces still attached to the roots. I never use decorative pots as the sole pot, I would use a cheap plastic pot from Chula Orchids or Kelley's Korner as a "liner" and then put that in the glazed pot for decoration. All of my phals are in semihydro and I use decorative pots to prevent the plants from tipping over and reduce algae formation.

[SG in CR]

If your media is fine enough to infiltrate between the rocks they won't offer any improvement in drainage long term, unless you put some sort of filter in between the rocks and the finer stuff above. I've found the cheap synthetic cleaning sheets do a pretty good job of it.
If you're media is coarse enough so that it doesn't fill in the gaps between the rocks I don't know if it will improve drainage, though water retention might be affected.
I'll put rocks in the bottom of pots that I expect might have a tendency to get tipped over, be it from wind or just a top heavy plant. A heavy base helps counteract that.
But in the case of epiphytic orchids I think one thing that get's confused is wet vs. lacking oxygen. I've seen a lot of orchids that supposedly can't handle wet feet remain perfectly healthy with roots that never dry out for months at a time when growing mounted outside. Rainy seasons here can sometimes be a bummer with months going by without a single day where it's doesn't rain. I think the issue with wet roots is more of an issue of roots that aren't getting any oxygen. When the water is a thin film over the roots and moss, it can diffuse through it readily. But enclosed in a pot that's a different matter, especially if you have a substrate that is decomposing and using up the oxygen. So you may want to make sure your pot isn't sitting flat upon a surface that doesn't allow for air exchange from the bottom of the pot. Lots of pots have little gaps in the lower rim to allow for this. But I've also seen pots that sit in saucers that pretty much form an airtight seal as soon as any moisture gets in between them. I sort of want to try putting small perforated pipes vertically in pots with more water retaining media just to see if the roots gravitate towards them.