SH in LECA versus Inorganic Conventional Culture
 

I have been growing orchids indoors and out now for 3 years and have been experimenting with several methods including SH. Half my collection of 150+ plants is in SH.
SH culture has many advantages as Ray has taught us, but may not be ideal for everyone, and definitely not every orchid type. SH is preferred now for all my new Catts that will be grown in GH.

The primary advantage of SH in my opinion is related to it using an inorganic media, and secondarily to ease of culture.
These are my observations.
Cattleya: Most Adapt quickly, grow well. Growing identical seedlings side by side SH versus conventional (bark+lava) I can say SH plants do not grow better. The tolerance of roots to constant moisture is temperature dependent and can be harmful if the GH is not kept warm enough. If your GH is unheated or growing area is cold (<50F for most Catts) let the media run dry-dryer in the winter with much less frequent watering.

Oncidium alliance hybrids, adapt slowly to SH and do not grow as well as in a fine well drained media even when adapted. Even the dryer growing species favor bark I found. Apparently SH culture has no advantage over retentive media for those orchids that favor a retentive media.

Aussie Dendrobiums: Do not like retentive media, and Love LECA or lava rocks, but not SH, give them drainage so the LECA can dry between watering.

Orchids types that favor mounts can be grown on LECA or lava in a net pot, but bark or mounts work better, some roots seem to prefer an organic surface over a mineral rich clay surface. On the other hand, Lithotropic orchids do like LECA but not SH culture. I'm not sure LECA works any better than Lava but is much lighter. Efflorescence-mineral build up is much worse on LECA than lava, or other rocks IMO.

Sarcochilus: Adapt but don't thrive. I learned this mix from the premier Australian Sarco grower who uses perlite, rock-wool, styrofoam mix. I have modified this and am growing Sarco in a mixture of rock-wool, perlite, and LECA but with some lava or stones to weight the bottom of pot (light weight media is great for shipping, not for my collection).

Rock wool is more water retentive than LECA, think of it as synthetic spaghnum moss. I suspect it can compress over time plus is expensive, thus the advantage of mixing in perlite / styrofoam or LECA balls. It should have the all the advantages of inorganic media but hold more water and not be dependent on a reservoir or tray like SH culture.

Rock wool inorganic mixes in various ratios are my new go-to for newly potted Sarco, Phals, and Oncidium alliance. I am experimenting with it for a few Catts, and can see those mixes eventually replacing SH in my Catt collection since it provides more flexibility in potting choice but still provides a steady moisture supply as with SH.

I grow many Catt types, and Aussies outdoors in LECA and Lava in pots with drainage. Avoid retentive media when growing outdoors as winter rains will create a water logged oxygen starved mess and kill the roots. Putting a thin layer of bark or Coco chips on top layer is initially beneficial but will cause problems eventually as it breakdown and settles. Since the Media is non retentive, frequent watering in summer is a must.

I have been experimenting with using polyester fiber, intended for filling pillows, instead of sphagnum moss or rock wool. It is very cheap and works well. It does not break down. It is bright white, so it takes a little getting used to.

Daddy, your observations are great - for your situation - but should not be used as recommendations for others, who have different overall growing parameters.

For example, I find that oncidiums do exceptionally well in S/H culture. (By contrast, I have never been able to grow D. bigibbum hybrids that way, yet many feel they are great "beginner S/H plants".)

I am also convinced that any plant CAN be grown in semi-hydroponics, but that does not mean that any individual can grow them all that way.

The bottom line is that:

• Being "niche" plants, orchids can be very specific in their needs.
• The number of cultural parameters is so great, that there are many ways to "skin that cat".
• What works for one, might be guaranteed plant murder for another.
• Almost anything CAN be used as a potting medium, but again, all the rest of your cultural "twists" must be able to work with it to meet the needs of the plant.

Interesting. Does the fiber retain water like sphagnum moss and slowly dry?

The polyester fiber is hydrophobic and seems to repel roots and organic growth (hence its utility in outdoor cushions) when I tried it.
Rock wool is hydrophilic quickly takes on algae growth and roots grow into it.

There are both hydrophilic and hydrophobic grades of rock wool. Personally, I have done best with a blend.

I bought a bag intended for stuffing pillows and used it as a pad under a Schomburgkia seedling mounted on a branch. It does retain some water. I would think a mass of even hydrophobic filaments would retain some water due to water's surface tension.