Pleurothallis has white substance in potting media

[etcherkate]

My poor little Pleurothallis gargantua seedling has suddenly grown a white substance on its potting media.

I wonder if the source of the problem is its neighbor, a Phragmipedium Don Wimber. Maybe two months ago, I noticed that the lowest leaf on the oldest growth of the phrag turned yellow and then brown. The leaf didn't become papery and easy to remove as I've observed in my phals; it is soft and firmly attached.

I isolated the phrag from the rest of the plants to see if the other leaves were affected, and when the brown didn't seem to spread, I reunited it with the others and hoped for the best. (The brown at the tips of the leaves is old, and watering the plant with bottled water instead of tap seems to have prevented the problem in subsequent growth.)

Could it be that the two plants are suffering from the same ailment, but showing different symptoms? Is there a way to effectively treat the problem without killing either plant?

Thanks in advance for your advice!

[estación seca]

First, Welcome to the Orchid Board!

That's how old Phragmipedium and Paphiopedilum leaves die. They turn soft and brown, at which stage they cannot be pulled off the stem easily. Then they turn dry and brown, at which stage they eventually come off easily. I let them stay on until they come off easily, with no tugging.

The white stuff on the tops of the moss in your Pleurothallis is mineral deposits. Water evaporates from the highest point and leaves behind the minerals it carried.

Orchids in the Pleurothallis alliance and slipper orchids like your Phragmipedium need very pure water. You can read your water quality report online at your water utility's Web site. If your water has total dissolved solids (TDS) of up to 50 parts per million (ppm) it is OK for your two plants. (Many other orchids tolerate TDS up to 500ppm or so, but not these two kinds.)

People with unsuitable tap water often get a reverse osmosis (RO) system to put under their kitchen sink. This provides pure water at a much lower cost than buying it in bottles. Also, if you have a large aquarium shop nearby, you can often buy RO water for less money than bottled water. Bring your own jugs.

Your plants look healthy, so it has not been a serious problem yet. Let us know how things go!

[Tindomul]

The plants look good, good luck with them. I would agree with Estación's conclusion.

Welcome to the Orchid Board by the way.

[etcherkate]

Thank you both for your very encouraging responses to my post!

Our local water utility's most recent report has the water TDS at 30 ppm. I'm confident that the leaves of the phrag improved after I started using bottled water, but it was also around this time that I began giving them "wet feet," letting them sit in an inch or so of water. I suppose this is another lesson in the importance of not changing too many cultural variables at the same time!

The next time I water, I'll be sure to give the pleurothallis a thorough flush, and I'll stay away from the tap water. Buying R/O water from an aquarium is an excellent suggestion that I will definitely look into.

Thanks again for the warm welcome and great advice.