What could cause root rot after repotting?

[tsun1108]

I had a couple of phalaenopsis which I bought from garden centres and they came in bark with tag saying they were last potted late 2011.

After flowering they were doing fine. When comes summer - am in NZ so it's summer now for us (and they are showing sign of new leaf & root), I decided to repot them in new bark.

Roots were good when I repotted, and I cut some of the old ones with sterile scissors (I worked in health related field so I have access to proper sterile tools).

Repotted them in new bark which had been pre-soaked the night before.

Didn't water for at least 10 days, thought kept them a bit on the drier side.

So this is the method I repotted my other plants in the past, they all did well with new roots and all re-spiked.

And 2 weeks later, both of the plants leaf started withering and I am talking about all of it..... so I pulled them out and all the healthy roots were now gone! Black, shrunken with even fungus on it.

What could've caused it? The only thing I can think of maybe the bark I used was not fresh enough seeing I bought them last year but they have been kept outside.

[RandomGemini]

Sounds like some kind of aggressive bacterial rot. I had this same thing happen to a phal I thought was doing fine. Had been overwatered by its previous owner and was given to me to save. I did the exact same things you did, then one day, it fell out of the pot and all of its roots were gone.

I ended up tossing it to protect the rest of my orchids. When I got finished cutting it back, it had three leaves and a small amount of stem remaining and might have recovered, but it would have taken years to recover from that kind of treatment.

[quiltergal]

Sometimes if you use too large a pot the center never really dries enough. When repotting the roots should just fit snugly in the pot. Pots should also have plenty of ventilation on the bottom and sides. Sometimes I will invert a small net pot into the bottom of the pot I plan to use. This helps get airflow up into the center so it dries at a similar rate to the top & sides. It could be your bark was partially decomposed though if you store it in a dry place that shouldn't be an issue.

If it has no roots I would toss it. Too much bother to try and bring it back from the dead IMO. Buy yourself a new one as a consolation prize and chalk it up to a learning experience.

[tsun1108]

Don't think it is the pot size problem.

I tend to use the smallest pot to repot, almost to an extent that I am bending the roots and scared that I would be breaking them!

The reason why I am suspecting it's bark problem it is because these were a bit old and when I opened the bag there seem to be some condensation inside.

[Ray]

When roots grow, they "tailor" themselves on a cellular level so that they function optimally in that environment, and once they have grown, they cannot change.

Move those roots into a different environment, and they may not function optimally and can fail.

That's why it is always best to repot right as new roots are emerging from the base of the plant. Those new roots will grow optimized for the new environment and support the plant, while the old ones fail.

This in not to say that it is an "all or nothing" situation - it depends to a large degree on the degree of dissimilarity in the conditions.

[PaphMadMan]

Rather than the age of the bark, or roots reacting to new environment, it is more likely simply the presence of a pathogenic fungus or bacteria getting into the cut or broken roots. The pathogen could just as easily (perhaps even more likely) come from the old mix rather than the new bark. It was harmless until broken roots gave it an entryway. This is different than when normally non-pathogenic organisms attack a weak plant because of sloppy habits or poor culture, and much harder to prevent.

[james mickelso]

Bingo. Trying to cram grown roots into a new pot invariably breaks them. Why did you soak the bark? The bark doesn't need soaking. the roots need water but not soaking. Wet bark is the perfect environment for bacterial and fungal diseases. Lots of folks grow orchids in lava rock and charcoal. It is sterile. The media doesn't need watering. The roots do. Root growth dictates when to repot. I disagree with you Ray. I have repotted lots and lots and lots of orchids into new environments and the roots don't care as long as they aren't broken or otherwise damaged. I have damaged roots and watched them deteriorate though. I have grow many phals just hung up with wire dangling in the air for a couple years and then potted them in moss and bark and lava and they do fine. As long as the root is not damaged they will continue to grow. Going from the air into a media changes the texture (openness) of the velamen. Take phal roots. When they grow in the air (some misname them air roots) it takes awhile before the velamen opens up and accepts moisture readily. In a media they open more quickly. But those in air do after awhile open more and accept moisture just as readily as older velamen. A great way to water phals or most any orchid is to put it in the shower and run water over it for a couple minutes. this simulates rain. For those stubborn "aerial" roots, you can take florists tape and braid it through the plant, over the roots, and force them down onto the media. But it's not necessary to do so. As they age they will get more and more absorbent.