changing size of bark?
 

If I go from large to small orchid bark when repotting, will the orchid go into shock and/or lose any existing roots or undergo any other issues?

I understand this happens if you change media type from organic to inorganic and vice versa.

Just curious, as I plan repotting some orchids later this year.

Thank you!

No. Generally.
The difference will be more in the amount of air and the free space in the medium and the new roots that will be formed. Why would you be making this change? In general I favor the bigger media possible as it promotes airflow and drainage. Smaller pieces are reserved for species with very fine roots or as additives to increase moisture for certain plants that need it

What type of orchid is this? Many orchids grow in very shallow pockets on rocks, bare root on rocks or trees, or in other ways that their roots are very much exposed to the air. When potting one of these orchids, the main purpose of the medium is to keep humid air around the roots. If the air is not able to circulate, the roots will succumb to root rot pathogens. The larger the medium, the better air is able to circulate.

"....will the orchid go into shock and/or lose any existing roots or undergo any other issues?
I understand this happens if you change media type from organic to inorganic and vice versa."

I grow nearly all my potted orchids in red lava rock. The orchids I buy are usually in a sponge-like plug, New Zealand sphagnum moss or bark. Some of the orchids I have transferred are either picky about having their roots disturbed (Angraecums, Psychopsis) or I have received them at the wrong stage of their growing cycle (Cattleyas) and needed to transfer them from broken-down medium. The trick I used for transferring orchids to rock is to 1) soak the roots for an hour or so while still in the old medium/pot,2) gently remove the orchid from the pot, shake off as much medium as possible, 3) carefully pick off the rest of the medium, then 4) hold the orchid and its roots in the new pot at the level I wish it to be and gently put the dry rock around the roots, tapping the bottom on the table now and then to settle it. If the orchid is not stable in the pot, I 5) stake or wire it so that it does not wiggle. 6) I do not water the orchid for a few days to give the roots a chance to heal from any scrapes, tears or cracks. The goal is to take good care of the old roots during the medium transfer. This preserves the roots and the orchid begins growing as if it has never been disturbed.

The least stressful time to change the medium is when there is new growth starting. New growth is usually followed by new roots.

I’ve gone from moss to bark and from fine bark to coarse bark. If the roots are healthy and not damaged during the repot they’ve adapted fine for me. Roots that aren’t in great shape at the outset have usually died shortly after the media switch. I don’t know if the trauma of repotting or the stress of trying to adapt to new conditions is what finishes them off.

Thank you for sharing your knowledge and opinions. I simply like the look of the smaller bark better, that's all. It seems the only disadvantage is possibly reducing the air and increasing chance of root rot.

I saw these lava rocks at the building supply store yesterday while looking at lava rock options (didn't get a photo, so, stole this off the internet). Are they big enough? :biggrin:

If you change for smaller bark you'll need to adjust your watering scheme (probably less waterings). Adding inert materials (lava rock, leka, etc) allows to keep an high air flow.

What kind of orchid are you moving from larger to smaller bark? I prefer Oncidium type orchids in small bark because I find it hard to keep them moist enough in large bark, so the only time I ever move from large to small is if I get an oncidium planted in large bark, which isn't a problem very often, because they usually come grown in sphagnum moss now (which I also dislike, however I will wait until new roots start to grow before I replant it in bark, as it seems plants sometimes take the change from moss to bark pretty hard)

I just bought large bark and perlite to mix at a kind-of-local shop, so, I won't be reducing size. If you're curious, they are a phal, dendrobium nobile, and zygopetalum.