Cut “dead” roots?
 

Just bought a rescue orchid from Lowe’s, it doesn’t have a good root system after removing the decay, theres roots without velamen, do I cut them or let them be so that it can absorb more water?

The orchids also dehydrated which im guessing is the cause of rootrot

I suggest leaving them - you have cleaned off the rotted stuff. Those "cores" of roots are actually functional, and can hydrate the plant, even if not terribly efficiently. (The dehydration was caused by root rot, not the other way around) They also serve to anchor the plant firmly in its new medium so that it doesn't wobble - really, really important. You can clean them up at the next repotting in a couple of years, by which time, if your efforts pay off, the plant will have good new roots.

Roberta, Do you have any reference articles about the vascular tissue remaining viable? You are not the first person to state that, but I’ve yet to find anything that backs it up.

Not picking sides here, although I have always been told once the velamen rots the root is useless in regards to nutrition absorption. However, in this situation, the remaining root cortex could be beneficial in providing stability to the plant after repotting.

I don't see any "sides" here at all. I'm just trying to discern the facts.

Velamen is merely the outer layer of dead cells anyway, acting as a "sponge" to hold water. I have read that it also actively traps nutrient ions, as well.

The trouble (in my mind) is that there is a lot more than velamen lost when roots rot, so I wonder if the xylem and phloem can remain functional.

http://cdn.biologydiscussion.com/wp-...18_thumb-4.jpg

Just trying to learn...

I don't have a reference, but have heard this said by enough experienced (and professional) growers, that I have to suspect there is some truth in it. As I have heard it described, some water can get up the root by capillary action (think "wet string") Certainly not great, but possibly better than nothing. The stability part is clear - if those roots are still firmly attached they can provide that much at least.

Unless they are contributing to the rot, ie, adding more dead material and clogging air flow, I see no reaso. To cut off what is there. It adds stability and I have seen “dead” roots grow new root all the time (mostly on Vandas but woody brittle roots with new white roots growing out of it.

Gonna hafta say "Nye" to that. "Experienced and professional growers" have also said that "orchids have to dry out between waterings" and that "semi-hydroponics won't work", both of which have been proven to be untrue.

At this point I'm not discounting the possibility that they contribute more than just mechanical stability, but I am skeptical.

I'm following this one closely. I would also like some Nyeintific research on that one, if any is around. I surely understand the stripping off rotten velamen, I understand the stability issue. I too have been skeptical about what that little white string may or may not be doing. A lot of experienced growers also do other stuff I may or may not do or agree with. For example, I whack away at ugly leaves that bother me. A lot of experienced growers say not to. But I raise plants by the "gut feeling" for the most part. Always have. Is this kind of like the peroxide conversation we had a ways back? As far as professional growers go... a whole different ballgame in my opinion. If professional grower means someone who grows/produces for profit. Way out of my culture or desire.

Experienced and professional growers also said that juvenile roots of catasetum plants shouldn't be watered too early (when the orchid comes out of dormancy) because they say that it kills the roots or stunts the roots and plant growth - which appears to be untrue after I had done some tests on a range of catasetum plants this season. The tests are going to continue next season, and the season after that - to draw a solid conclusion on it. At the moment - it appears that as long as the roots and media don't stagnate due to water-logging and good air flow is maintained through the pot and media, then nothing bad will happen to juvenile catasetum roots that are watered for catasetum plants coming out of dormancy.

As for the string roots with velamen gone ----- one test will be to just cut off an aerial root (or any long enough orchid root), then make an accurate note of which end is the 'upper portion' (maybe it doesn't matter - but should do it - just in case), and then carefully strip off the velamen if possible, exposing the 'string'.

Then dip the 'string' (tail end) into a cup of water. And clip the top end of the stripped root to the top edge of the cup - with a paper clip or some other clip.

Then use a coloured blotting paper every once in a while to touch the upper portion of the bare root - which is to see if it stays moist for days or weeks on end.

The test can involve roots of various kinds of orchids, and important details should be included - such as length of cut root, and distance of tail end dipped into the water (below the water surface) and distance of moisture test along the root above the water surface - as it will be interesting to know the height at which the water can be wicked above the water line - that's if it does any wicking at all. And one more all-important condition to find out about is - whether the wicked water (if any) will enter the orchid for hydration.

And back to the 'dry out between watering' for regular orchids. I agree that - as long as the roots are adequately aerated (which can also mean good air flow in media and around the water in the media), then an orchid can survive - assuming other requirements are met too, such as temperature, lighting level etc.

My interpretation of 'drying out between watering' is along the lines of - no need to do this regularly - but doing it sometimes (every once in a while) - could possibly help to keep certain organisms under control or in check, or even prevent them from growing. That is - to give 'unwanted' organisms (eg. algae, bacteria, etc) a hard time, or prevent them from growing or getting out of control.

It's not that algae etc. are immediate threats ----- but maybe rather a chain of events that could occur - eg. growth of algae in media and/or on roots is condition A, which could (possibly, but not necessarily) lead to condition B, C etc over time. Condition B could be say 'death of algae', and condition C could be say rotting or bacteria build-up. So, drying out every once in a while could be beneficial here. And the case of 'drying out between watering' for every watering is really an extreme case of this.

The focus isn't necessarily on algae. Drying out every once a while could possibly cut down on other sorts of unwanted organisms building up in the media (or cut down on chances of them growing).

“The typical orchid root has a stele of comparatively small diameter. It is surrounded by a cortex which is further enveloped by a highly specialized exodermis, most of which at maturity do not contain protoplasm. A few cells, however, are living and allow the passage of water through them.”

Velamen - Wikipedia

So correct me if im wrong, i’ve been reading up to understand, if the velamen is a sponge of dead compact cells around the cortex to bring in the essentials, and the cortex has some living cells, would it be appropriate for it to continue to bring in (not as much) water that’s available regardless of having velamen, or once the velamen decays does the cortex loose its function aswell? Sorry if this is a bad question, just trying function of orchid roots- Newbie!

Here is a good diagram of a typical monocot root (cross section): link

the velamen is an orchid adaptation. it's a layer of dead cells on the outside (on top of the exodermis/epidermis, which is almost mostly dead) that is highly efficient at absorbing water and nutrients - basically a sponge, like you said.

the cortex makes up the majority of the root. in the middle of the root is the "pith," which is basically undifferentiated plant cells that store some nutrients. outside of the pith is a ring of water vessels (vascular tissue, which is specialized/differentiated) which transports water and nutrients throughout the plant. between this ring and the epidermis (the outside) is the cortex. the cortex is made up mainly undifferentiated living cells with thin cell walls, and their main job is to carry water/nutrients to the vascular tissue.

most plants don't have velamen - they do just fine taking up water with their epidermis. so, without the velamen, the orchids should still survive. they just won't be as efficient at absorbing nutrients. since the velamen is an important adaptation, they might be worse off without it, but the roots are still functional. I'm sure in nature orchid roots aren't all pretty and perfect, completely covered in velamen.

tl;dr: orchid roots are still functional without velamen. the water goes from velamen -> exodermis -> cortex -> endodermis -> vascular cylinder -> rest of plant. most plants only have an epidermis, so water goes from exodermis -> cortex -> endodermis -> vascular cylinder -> rest of plant.

when the article said: "It is surrounded by a cortex which is further enveloped by a highly specialized exodermis, most of which at maturity do not contain protoplasm. A few cells, however, are living and allow the passage of water through them,"

they meant the exodermis is mainly dead but has some living cells. the cortex is fully living. btw, I don't think water only goes through the living cells in the exodermis, since clearly water can be absorbed by the velamen, which is fully dead.

wow that was long sorry. :P

Thats okay! I love a good read especially about the things I’m interested in, I’m 5 months in this orchid frenzy, making plenty of mistakes but learning lots from it. The explanation you gave is what I was looking for, thank you!

I think Southpark has nailed the testing regimen - good luck doing that.

Both Lauren and Neo raised my area of concern - If the velamen is gone, the root ought to still function, but if everything but the pith is dead and rooted, the vascular cells seem unlikely to stay alive. They might wick, but I doubt they can actively pump water and nutrients.

Southpark - I believe the origin of "orchids must dry out" was based upon a misinterpretation of poorly chosen media.

When I started growing, I read several articles referring the grower to head into the woods to collect components to blend, and that often resulted in media that were much too compact.

Too compact = gas exchange pathways blocked with water = root suffocation and death. Let the medium dry and the pathways reopen, negating the issues.

In other words, the orchids didn't need to dry out, the medium did.

Without getting into all the fancy scientific components of the root, I second Ray's concern. If the velamen has rotted and gone, even though it is a layer of dead cells, my interpretation is that it is an indication that the remaining components of the root (insert scientific terminology here), which I will just call the "stringy" part, have also died. So we would need to determine whether that "stringy" part still consists of active, living cells capable of transporting water and nutrients or if that "stringy" part is now dead and unable to perform it's function anymore.

I totally agree with you and Ray on this. It will be interesting to find out if a particular stringy part can not only wick, but also whether that wicked water (if any) can get into the orchid for hydration. This is what you were meaning already - as in performing its function, and I fully agree.

I agree! So y'all get out there and start testing and figure it out. I'll be here when you're ready to release the results!:bowing

I think part of the issue is that it’s just difficult to determine whether a root is actually dead. I’ve had Phalaenopsis with roots with stretches of exposed core interspersed stretches of intact velamen. I initially thought that the the exposed core section must be dead and therefore the root below that section was not contributing to the plant, but cutting such roots at the exposed section invariably led to dramatic wilting so I think I was wrong about it being dead.

With Oncidium types I used to cut “soft” roots where the velamen was no longer attached to the core and came off easily. I thought these were dead, but I’ve seen some of my plants push new growth from these roots and plants recover much more quickly when these roots are left intact.

I don’t think it’s a case of dead roots hydrating the plant as much as it’s a case of me being a poor judge of when a root is entirely dead. This has lead me to be much more conservative when it comes to pruning roots on plants with poor root health.

maybe we can go the kindergarten route and place the stringy part in colored/dyed water and see whether the dye travels up the root. :)

I remember when we used to do that with celery sticks :D

---------- Post added at 12:55 PM ---------- Previous post was at 12:19 PM ----------

aliceinwl - I totally agree... it's hard to tell when roots are actually dead. honestly, unless there's a serious/obvious infection, it's probably best to just leave them there!

Absolutely! And - for the science people in testing labs, they can help us to put trace elements into the reservoir. And if any of those trace elements get picked up in leaf samples etc, then they would be able to have this sorted very nicely.