I have been growing in NZS since about 1988. I grow flasklings exclusively in New Zealand Sphagnum, and have since about 1989.
Why do I prefer NZS? Because, first, I get substantially better growth. We all know the old Orchid business model of growing the same plant for years on the bench is history. Turnover is the name of the game. NZS reduces time to market. Second, plants in NZS in plastic pots (the small ones) use about one tenth the amount of water, and need to be watered half as often as plants in bark. The plants in terra cotta use more than the plants in plastic, but they still use significantly less water than plants in bark (in plastic pots), and can be watered on about the same schedule.
I began to wonder if you could just leave the plants in the NZS, and began to grow larger and larger plants in NZS. Like many other people, I noticed that in pots at about 6 inches, it seemed to pack down and smother the roots. I started using a layer of styrofoam packing material in the bottom of the pot. This seemed to help. I started using more, so that the layer of NZS was no more than about 2 inches thick. This worked great, but now the Phals, which would grow huge in in the NZS, would topple the pots over that have no mass when the moss dries. This was especially true when they were in spike, and ready to market.
After considering adding some sort of ballast, I switched to terra cotta pots for the larger plants. Over the years, I have "discovered" that you can grow very large plants in NZS, but unless you want to lose the roots periodically, you need to let the larger plants go much drier between waterings.
My primary wholesale product is now grown in 5-1/2" terra cotta azalea pots (3/4 height) in NZS. I tend to let them dry enough between waterings that I do not get the same algae and live moss growing on the surface that I used to, (or still get on the seedling trays.) The roots are plump, white and there are very few dead roots when I repot these plants.
The largest plastic pots that I grow Phals in NZS are 3-1/4".
I do not pack the moss tightly for Phalaenopsis. I get significantly better root systems on the same plants that come from Taiwan in reallly tightly packed moss, AFTER I put them into looser moss. The larger the pot, the less I pack the moss. This seems to be really important to success in larger pot sizes. The roots will brace the plant against the sides of the pot, and hold the plant firm; packing the moss tight enough to lift the pot by the plant will only result in less roots or loss of roots, in my experience. I have not tried the technique of alternating several layers of moss with inert material, as some have described here, (in the IPA Digest) but that sounds like a good idea based on my experience, as long as the inert material does not add to packing the moss down.
I have two problems with over-packed moss. One, there is less air movement around the roots, and that causes them to smother. At repot time, as many as half the roots will be dead on those plants. (Yes, I could be over-watering them for the density of the moss.) Two, percolation is to the root sytem what air movement is the rest of the plant. I get better growth when I can water once or twice a week. Some of those plants tightly packed in moss, can go three weeks between waterings during the winter. It might save on labor, but I want to see the product turn over sooner, and I believe that the more often you percolate, the better the plants grow.
Water quality is also important when considering moss. One advatage to using NZS is that you can repot virtually anytime; (assuming your moss is in good shape, and there are very few dead roots), by wrapping a bit more moss around the old root ball, and placing into another pot. This saves money on the moss, as well as not setting the plant back. Unfortunately, if you have "bad" water, the moss is not going to be in very good shape after 18-24 months, and you may have to replace the entire potful of moss. Undesireable for several reasons.
I have about 900 ppm of dissolved solids in my well water. I still manage to get over 24 months out of my moss. Which means for most plants, you can still find the original moss from the plug tray or 2-1/2" pot, in the middle of the 5-1/2" product when it gets marketed.
Do I grow everything in NZS? No. When plants come in bark, they get put back into bark when they get repotted. When they come in ANY sort of moss, New Zealand, Chilean, or even peat mixes, I repot them into NZS. Why? It seems that different types of roots develop in the two media,(bark and moss) and it takes some time to grow a new root system when changing media. Time is money, and so I do not change media if at all possible. I do however grow basically all my Phal product in NZS, starting from right out of the flask, and continuing to market.
Posted to the International Phalaenopsis Alliance Digest, 3/14/04