Removing yellowing leaves

[gego]

I believe there are reasons why older leaves die, for leaves 4-6 leaves down from top, it could be a natural thing for the plant but for 2-3 leaves from the top, something is wrong. I wish I can just keep all the leaves intact just like some in the wild I've seen.

 

[gonewild]

I believe there are reasons why older leaves die, for leaves 4-6 leaves down from top, it could be a natural thing for the plant but for 2-3 leaves from the top, something is wrong. I wish I can just keep all the leaves intact just like some in the wild I've seen.

If you have trouble keeping older leaves and the new leaves and roots are healthy it may be a result of low humidity.

 

[naoki]

Rethink that.....Decaying vegetation does in fact release ethylene gas.

That's true, and I didn't think about it. But it it is probably a negligible amount. Not many bacteria emit ethylene, but some fungi appear to produce ethylene as byproduct. In the following study, they had to enclose the plant with soil in small bottles to see the effect (maybe abstract only):
http://aem.asm.org/content/54/11/2728.short
It will be even smaller amount for epiphytic orchids.

The need (benefit) for cultivated orchids to translocate nutrients from old leaves before they are shed is eliminated by providing fertilizer and an elevated nutrient supply that is not found in nature.

What is the main nutrient in plants? It is true that nitrogen is the most studied element for the relocation/remobilization during the leaf death, but there are several studies showing the carbon reallocation (in forms of lipid, amino acids, and sugar). Carbon assimilation is a costly operation for plants. But setting my nitpicky comment aside, I agree that nutrient recycling from old leaves probably have a relatively small impact under cultivation.

Removing dead leaves has always been considered an important part of greenhouse management, and actually often required by agriculture inspectors in licensed nurseries. There are plenty of published documents that address the reasons why removing decaying and dead leaves is beneficial to plant health but I have not seen any yet that prove or justify a benefit to leave old leaves on orchid plants.

Can you possibly tell us a couple publications (I'm not doubting you; if you already know about them, it would save me time)? In greenhouse, where you need to spray pesticides, old leaves could be problems because it provides places where pests can hide. So it is a common practice, but I was just curious if someone really quantified the magnitude of benefits.

Naoki,
Interesting paper.
I wonder why abscission zones did not evolve in paph leaves?
Maybe the dead leaves play a part in acting as a barrier on the ground and encouraging humus and detritus to accumulate near to the plant, ultimately providing food.
They may also shade and protect the roots from the sun for some time after their death.
Regards,
David

That's an interesting idea. Sometime we get into the trap of thinking that everything has some adaptive significance, but the trapping mechanism might give some advantage.

 

[Stone]

Removing any green material (or reducing the mass) from any plant will reduce growth however little that may be. Pruning just one branch from a shrub will reduce root growth. It does not necessarily mean much in most cases but it certainly does nothing to help the plant so why do it if you don't need to?

 

[gonewild]

That's true, and I didn't think about it. But it it is probably a negligible amount. Not many bacteria emit ethylene, but some fungi appear to produce ethylene as byproduct. In the following study, they had to enclose the plant with soil in small bottles to see the effect (maybe abstract only):
http://aem.asm.org/content/54/11/2728.short
It will be even smaller amount for epiphytic orchids.

The amount from a single leaf is not much but consider the amount from a greenhouse full of plants with old leaves as being a potential problem. And add too that the decaying organic matter in the potting media (bark, peat moss, ect)

What is the main nutrient in plants? It is true that nitrogen is the most studied element for the relocation/remobilization during the leaf death, but there are several studies showing the carbon reallocation (in forms of lipid, amino acids, and sugar). Carbon assimilation is a costly operation for plants. But setting my nitpicky comment aside, I agree that nutrient recycling from old leaves probably have a relatively small impact under cultivation.

The leaves on a Paph got there in the first place because the plant had enough nutrients from fertilizer to build all the leaves... without the aid from relocating nutrients from old leaves. So the loss of un-relocated nutrients by removing an old leaf is easily offset by nutrients from the fertilizer supplied.... That is why we apply so much fertilizer in cultivation!

Can you possibly tell us a couple publications (I'm not doubting you; if you already know about them, it would save me time)? In greenhouse, where you need to spray pesticides, old leaves could be problems because it provides places where pests can hide. So it is a common practice, but I was just curious if someone really quantified the magnitude of benefits.

It's your turn to find studies that show leaving old leaves in a greenhouse is a good idea! I'm interested to see what you come up with.

Here are 4 from a google search page. Granted they are not science peer reviewed papers but they are horticulture peer known facts based on science.

http://www.oardc.ohio-state.edu/joneslab/images/ethylene_extension.pdf

http://content.ces.ncsu.edu/ethylene-sources-symptoms-and-prevention-for-greenhouse-crops

http://www.agf.gov.bc.ca/ornamentals/floriculture/ethylene.htm

https://u.osu.edu/greenhouse/2014/0...he-production-greenhouse-sources-of-ethylene/

 

[gego]

Removing any green material (or reducing the mass) from any plant will reduce growth however little that may be. Pruning just one branch from a shrub will reduce root growth. It does not necessarily mean much in most cases but it certainly does nothing to help the plant so why do it if you don't need to?

Agree on this. If the culture is right and adequate nutrients are provided, those leaves should not turn yellow or yellowish.

 

[troy]

Read post 7

 

[gonewild]

Here is some info that tells the levels of ethylene gas that cause damage.... 100ppb

But how many old leaves does it take to make 100ppb in the growing area?
Maybe no one knows so they just remove the old leaves.

 

[abax]

Stone, I'm a nursery person and used to have a garden
center for retail of all types of plants. I base my opinions
on years of experience. The health and beauty of most
nursery grown plants depends on appropriate pruning
techniques applied at the proper time to avoid decaying
plant material from causing bacterial/fungus infection on
old growth. When one prunes a shrub or tree, one forces
the plant to develop more and deeper roots and facilitates branching. I think the same applies in good orchid greenhouse management. Dispose of dead or
dying leaves and seal the cut. Keeping the growing environment clean is of utmost importance.

 

[Happypaphy7]

I believe the practice of cleaning up the dead leaves are literally for cleaning purpose, at least that is the main purpose. It just makes the growing area look better.
Certain disease organisms and even insects might stay on dead plant material and getting rid of these makes sense.
However, I believe fungi responsible for breaking down of dead plant material are different than disease-causing ones that live on live plant materials.
All in all, getting rid of dead material is good.

Pruning does stimulate certain plants to grow or flower better ( roses for example), but I guess different plant require different care to do best.

For orchids, I do not think it is needed to prune unless they turn yellow/brown and die on its own, except for the diseased leaves which should be removed to prevent spreading further.

 

[gonewild]

It's too hot to go outside so I've been reading about old leaves.
There is a lot written about the benefit of removing and clearing away old leaves but I have yet to find any published reason to leave them on the plant...any kind of plant.

A few places have eluded to the idea that plants may use old leaves as a dump for excess salts and toxic compounds. The suggestion is dropping them off is like throwing out the garbage.

The leaf is also abscissed to regulate the flow of auxin, ethylene and other hormones. dropping the leaf keeps auxins produced in the old eaves from moving to new forming leaves.

Here are a few interesting links related to old leaves:

http://agridr.in/tnauEAgri/eagri50/PPHY261/lec24.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC541608/

 

[gonewild]

This one completely outlines the ethylene gas problem. every wonder why a bud blasted for no reason? Many other maladies without obvious answers all have symptoms of ethleyne damage.

Known Fact: yellowing and decaying leaves produce excessive amounts of ethylene gas.

Unknown fact: What is the volume of ethylene that is produced by a few dead/dieing leaves?

This is a huge support for the need to remove old leaves from the plant and growing area.
I cant find a supported reason for leaving the old leaves on the plant.

This article is easy to understand and is related to plants and flowers:

http://www.greenhousemag.com/article/gm1112-crops-preventing-ethylene-damage

 

[C. Rothschild]

Some plants are easy to repot and don't mind it so you can just remove the whole leaf. Others hate it and it damages the roots so just cutting it off is okay for a little while.

 

[Stone]

Stone, I'm a nursery person and used to have a garden center for retail of all types of plants. I base my opinions
on years of experience.

So am I, so did I, and so do I

The health and beauty of most
nursery grown plants depends on appropriate pruning
techniques applied at the proper time to avoid decaying
plant material from causing bacterial/fungus infection on
old growth.

I agree the pruning enhaces the beauty and sometimes (but not often) the health of a plant. Some things, modern roses for example, simply must be pruned or they stagnate.

When one prunes a shrub or tree, one forces
the plant to develop more and deeper roots and facilitates branching.

Pruning does force branching but it definitely inhibits root growth...at least for a time. The whole bonsai concept is based on that. Top pruning reduces root growth and root pruning reduces top growth.

Keeping the growing environment clean is of utmost importance.

This is often quoted but I wonder about the science behind it. The types of pathogens that attack plants are different species from those that decompose plant material, cause slime etc.
Certainly a clean greenhouse makes us feel better.

 

[Stone]

I believe the practice of cleaning up the dead leaves are literally for cleaning purpose, at least that is the main purpose. It just makes the growing area look better.
Certain disease organisms and even insects might stay on dead plant material and getting rid of these makes sense.
However, I believe fungi responsible for breaking down of dead plant material are different than disease-causing ones that live on live plant materials.
All in all, getting rid of dead material is good.

Pruning does stimulate certain plants to grow or flower better ( roses for example), but I guess different plant require different care to do best.

For orchids, I do not think it is needed to prune unless they turn yellow/brown and die on its own, except for the diseased leaves which should be removed to prevent spreading further.

You stole my words. Or I stole yours. I read this after I wrote my reply.

 

[abax]

mea culpa! May we agree to disagree? ;>)

 

[cnycharles]

The possibility of leaves giving off ethylene is another reason why encouraging air movement is a plant healthy practice

 

[naoki]

Thanks for a couple interesting links. Here is the nutrient recycling rate in orchids:
https://www.researchgate.net/public...ves_of_vascular_epiphytes_from_lowland_Panama

It include only NPKCaMg, and the major part (Carbon resorption) is not considered. It is true that if there is plenty of mineral nutrients in cultivation, only the limiting elements may be recycled. But most people aren't fertilizing with C. There are other studies (especially in non-orchids), but I'm a bit tight in time now.

With regard to Angela's point of pruning, there are interesting studies in plant herbivory (bugs, zebras etc eating plant leaves). Pruned plants (mimicking herbivory) created a larger above ground biomass (meaning weight of leaves and stems). This is partly because it removes apical dominance (promoting the branching). Also some plants appear to over-compensate for the loss of the leaves. So some people thought that herbivory could "help" plants (which is a weird idea). With longer term studies, the plants pruned weren't as big as control. So as Mike said, they probably sacrifice roots and reallocate the energy temporarily to make more above ground leaves after pruning. I learned about this long time ago (around 1990's), so the details may be a little off, but I think the general story is right.

 

[gonewild]

But most people aren't fertilizing with C.

Thanks for the recycling link.

Yeah, the problem with C recycling is that the atmosphere is deficient now. oke:

Back to the point of the thread... There seems to be no valid reason to leave yellowing, dieing or dead leaves on the plant.

 

[tnyr5]

I yank em off. My plants exist for my aesthetic amusement. If they don't look nice, there's no point in having them.