Do cannabis plants really 'cannibalize' their own leaves?

[Humanrob]

For years I and others have referenced that when a cannabis plant is lacking nutrients in the soil, they will take nutrients from their existing leaves. I realized I have no idea where I got that information, and that while it seems on the surface to 'make sense', I have no idea if it's true. From a botanical standpoint, is this accurate? Or just Bro Science? I tried to do google searches on this and I can't find any information to back that up.

An alternative paradigm would be that the the fan leaves that change color and eventually die when a plant is lacking available soil based nutrients, are simply being abandoned by the plant. This would imply that the plant is able to prioritize where limited resources are distributed, and it focuses on it's reproductive imperative.

This is relevant in terms of defoliation techniques, because either (A) removing leaves removes a resource for the plant in terms of accessible stored nutrients, or (B) we are enabling the plant to direct its limited resources away from the leaves, which take a lot of energy to support, and 'helping' it focus its energy on the buds. Of course, it's entirely possible that neither of those scenarios represent how plants actually work, I really have no idea.

 

[blue]

Good topic Humanrob ... especially with the new Schwazzing techniques people use .. you gotta wonder how the plant could live if it were relying on its leaves to cannibalise!

Lets see some science!!

 

[Humanrob]

Good topic Humanrob ... especially with the new Schwazzing techniques people use .. you gotta wonder how the plant could live if it were relying on its leaves to cannibalise!

Lets see some science!!

Exactly! I'm schwazzing for the first time which got me thinking...

And thanks for the rep!!!

 

[Delps8]

Fan leaves server many purposes including providing nutrients to plants during flower.

"you gotta wonder how the plant could live if it were relying on its leaves to cannibalise!"
By removing older leaves, you are depriving the plant of needed nutrients. It doesn't kill it, obviously, but, seeing that the nutrients are not available for the flowering plant, it will tend to impair the plants' ability to reach its genetic potential.

 

[Humanrob]

Fan leaves server many purposes including providing nutrients to plants during flower.

"you gotta wonder how the plant could live if it were relying on its leaves to cannibalise!"
By removing older leaves, you are depriving the plant of needed nutrients. It doesn't kill it, obviously, but, seeing that the nutrients are not available for the flowering plant, it will tend to impair the plants' ability to reach its genetic potential.

If you don't mind my asking, how do you know this is true?

 

[Olderfart]

For years I and others have referenced that when a cannabis plant is lacking nutrients in the soil, they will take nutrients from their existing leaves. I realized I have no idea where I got that information, and that while it seems on the surface to 'make sense', I have no idea if it's true. From a botanical standpoint, is this accurate? Or just Bro Science? I tried to do google searches on this and I can't find any information to back that up.

An alternative paradigm would be that the the fan leaves that change color and eventually die when a plant is lacking available soil based nutrients, are simply being abandoned by the plant. This would imply that the plant is able to prioritize where limited resources are distributed, and it focuses on it's reproductive imperative.

This is relevant in terms of defoliation techniques, because either (A) removing leaves removes a resource for the plant in terms of accessible stored nutrients, or (B) we are enabling the plant to direct its limited resources away from the leaves, which take a lot of energy to support, and 'helping' it focus its energy on the buds. Of course, it's entirely possible that neither of those scenarios represent how plants actually work, I really have no idea.

Put another way, your question is whether nutrients are mobile in the sense used by horticultural discussions. I can't provide proof one way or another because I can't find any original research on the topic. However, given that every horticultural reference I have managed to look at says that the same specific set of nutrients are mobile and the rest are not, I suspect the research is out there somewhere, likely buried in decades old stuff that is less easy to get at. I will be interested to see what others here come up with.

 

[Humanrob]

Put another way, your question is whether nutrients are mobile in the sense used by horticultural discussions. I can't provide proof one way or another because I can't find any original research on the topic. However, given that every horticultural reference I have managed to look at says that the same specific set of nutrients are mobile and the rest are not, I suspect the research is out there somewhere, likely buried in decades old stuff that is less easy to get at. I will be interested to see what others here come up with.

I hear what you're saying, it's possible that my question is so "Botany 101" that no one is going out of their way to talk about it because it's such an established basic concept.

So far the closest thing I've been able to find actual data on, is the confirmation of the similar paradigm that deciduous trees re-absorb chlorophyl in the fall before the leaves drop -- so there is a precedent for the idea that plants can reuse resources stored in leaves. I'm still looking for more information, I suspect it comes down to the right search criteria, just haven't found it yet.

 

[Humanrob]

My wife and I are old enough to actually own a lot of books, I forget this sometimes. Page 162 of Botany for Gardeners by Brian Capon:

"Prior to leaf abscission, some of the nutrient elements (including nitrogen, potassium, and magnesium) are released from their bound form in protein, chlorophyl, and other molecules and transferred from leaves to the plant's growing tips for reuse. Because mineral relocation is in progress when older leaves turn yellow, gardeners can help their plants conserve nutrients by not removing discolored leaves for several days, until the minerals have been transferred."

So, this appears to be at least true in general, and I suppose we can assume it's true for cannabis plants?

That reinforces the notion that since Schwazzing is denying the plant the option to (at least to some degree) self regulate its distribution of nutrients and supplement new growth with stored resources, feeding Schwazzed plants not too much and not too little is more critical than with conventionally grown plants. Damn, I hope I can pull it off.

 

[Humanrob]

Thanks for the rep @Frank the Dank !!! Learning never stops.

 

[Olderfart]

My wife and I are old enough to actually own a lot of books, I forget this sometimes. Page 162 of Botany for Gardeners by Brian Capon:

"Prior to leaf abscission, some of the nutrient elements (including nitrogen, potassium, and magnesium) are released from their bound form in protein, chlorophyl, and other molecules and transferred from leaves to the plant's growing tips for reuse. Because mineral relocation is in progress when older leaves turn yellow, gardeners can help their plants conserve nutrients by not removing discolored leaves for several days, until the minerals have been transferred."

So, this appears to be at least true in general, and I suppose we can assume it's true for cannabis plants?

That reinforces the notion that since Schwazzing is denying the plant the option to (at least to some degree) self regulate its distribution of nutrients and supplement new growth with stored resources, feeding Schwazzed plants not too much and not too little is more critical than with conventionally grown plants. Damn, I hope I can pull it off.

There is another complexity to this issue. I have read (but don't recall a link) a research paper that confirmed that any fans seeing less than ~200 PFD are sinks rather than a sources of photosynthetic products, which I take to mean that heavily shaded leaves (at least the ones I have checked with my par meter) might as well be chopped because they are not net producers, and may be using resources better spent elsewhere.

As a consequence, I do not feel bad about thinning the lower canopy to make sure that there is enough air circulation, and I do not worry about whether the leaves are dead/depleted yet. I will provide the plant with what it needs with the salt nutes. Other than ensuring air circulation, I don't remove leaves.

The other aspect to the 200 PFD finding is that any leaf that does received 200 pfd is a producer, and removing it will reduce the photosynthetic production of the plant. @Mañ'O'Green has posted commentary before showing that even his lower buds not receiving significant light do very well in his grows, and that suggests, if not confirms, that production by all leaves is available to a degree to all buds, not just the adjacent ones.

Happy growing mate, and thanks for bringing this interesting topic up.