ive had this arrangement on my breakfast table for the last year. It hasn't changed much except for the orchids, which i replace every two to three months.
1. 10 -12" glass bowl, mine is from Target, ~$6. I like glass so i can see the moisture level.
2. the bottom is a one inch layer of hydroton, for drainage. expanded shale can also be used. these keep the soil from sitting in water and have an absorbent outer layer that wicks water upward.
3. next is a layer of potting soil, i used Pro-mix. any professional peat based soil mix is fine, but it needs to wick well so there are no dry spots after watering. I like miracle gro potting mix also.
4. Add plants!
your orchid stays in its pot, so place that in first. i used two mini phalaenopsis in three inch pots.
add a layer of soil to anchor the position of the orchids.
add other plants directly into the glass bowl and top off with soil.
the soil should not reach more than 1/2" below the rim of the bowl. you don't want water running off onto your nice table.
5. i water the orchids, until the Hydroton layer is full of water. in a couple of hours the entire bowl of soil is evenly moist and there is no more water standing at the bottom.
* I once had a 4" regular sized phalaenopsis in the bowl. the pot was too high, so i cut off the bottom and stuck the pot in the soil, concealing the rim with moss
*orchids grown in bark lasts much longer than ones grown in sphagnum moss.
*for the first month i added dilute organic fertilizer but the plants did not like it. since the water doesn't run off, i don't think the plants even need it. I've used no fertilizer whatsoever for the past year, yet the plants have grown and filled in well.
*these are growing near a north and west facing window. the bright afternoon sun is too much, so the blinds stay closed. yet the north window doors not provide enough light to get the orchids to rebloom. i just take them out once they are faded and give then to my mom. she gets bright indirect light which allows them to rebloom within a few months.