Change substrate of a stressed plant
 

I have 4 orchids in sphagnum moss with some dead roots. I want to switch them to a mix of bark and coconut husk and cut the dead roots.

Yesterday I bought a LED lamp to compensate the light coming from the window. I watered them recently and they are still wet.

My question is : Is it better to let them get used to the LED light and let them dry then change the substrate or I can do it right now?

Getting used to improved lighting shouldn't be stressful for a plant. If it is stressful for the plant, that typically means the lighting change was made too quickly. Repotting wouldn't normally impact that transition unless the plant is in bad shape, and if that's the case you'd be better off repotting asap anyway.

So, my vote is to repot now. I prefer removing sphagnum from phal roots when it's wet. Wet roots are more pliable/flexible too.

Yes, you can repot now.

Be conservative when it comes to cutting dead roots. It isn't always obvious as to what is "dead". If the velamin (the coating on the outside of the root) comes off easily you can remove it, but if the core of the root is not rotted, it can still hydrate the plant, and at any rate can help anchor it in place in the fresh medium. Having the plant held firmly in place is vital for new roots to grow without damage, so leaving the core of old roots in place facilitates that.

If the plant has been growing in sphagnum, it’s existing roots are “attuned to”, or “optimized for” growing in sphagnum, and will not be for a different potting mix. That means the existing roots will start to fail, and the plant will need to grow new roots that are attuned to it.

For that reason, the ideal time to repot is just when new rots are emerging from the base of the plant, but if waiting risks losing more roots and possibly the plant, go ahead anyway, but be prepared to “baby” it a little by keeping the plants warm (a seedling heat mat works great) and humid, to slow water loss. I just invert a clear plastic bag over the plant and pot (unsealed) to act as a mini greenhouse.

Thank you very much for the help.

Will it help to add a little orchid fertilizer (1/4 concentration)?

If the roots are bad and the plant can't take up water (with or without nutrients), fertilizer is of no use. Think of fertilizer as "vitamins" not food... green plants make their own food (carbs) through photosynthesis. It can coast along without fertilizer for a long time, when new roots appear, it will be able to utilize the fertilizer. At this point, follow Ray's advice to maximize humidity so that it doesn't desiccate, and let it do its thing.

We've all been operating on the assumption you have Phalaenopsis orchids. Do you know what they are? Or can you post a photo?

My group picture with my LED light

[IMG]https://live.staticflickr.com/65535/...a8479015_z.jpg20220219_204230 by Stan Louka, on Flickr[/IMG]

Now My Orchids:

[IMG]https://live.staticflickr.com/65535/...93532b62_z.jpg20220219_204353 by Stan Louka, on Flickr[/IMG]

[IMG]https://live.staticflickr.com/65535/...8129c8ea_z.jpg20220219_204345 by Stan Louka, on Flickr[/IMG]

[IMG]https://live.staticflickr.com/65535/...cf3fb470_z.jpg20220219_204330 by Stan Louka, on Flickr[/IMG]

[IMG]https://live.staticflickr.com/65535/...79f28c2f_z.jpg20220219_204305 by Stan Louka, on Flickr[/IMG]

[IMG]https://live.staticflickr.com/65535/...59c8df52_z.jpg20220219_204255 by Stan Louka, on Flickr[/IMG]


I think my orchid has some fongus on it roots, what can I do?

[IMG]https://live.staticflickr.com/65535/...c61f356d_z.jpg20220219_204401 by Stan Louka, on Flickr[/IMG]

The fungus (mold) won't hurt anything. When you repot, and get the roots into a healthier environment, the problem will solve itself. But it won't harm the plant in the meantime. Those plants actually look quite good.