Overfeeding: toxic salt accumulation or ph causing lockout?

Hi Guys,
I've got many years of growing behind me and I spend a lot of my RUI time helping noobs with plant problems.

One very common problem is overfeeding and nutrient lockout.

I'm seeking a better understanding so that my guidance is based on knowledge.

So assuming soil, coco or soil-less. When overfeeding occurs, nutrient salts accumulate in the medium. And ph drops.

So my question is: Do the nutrient salts themselves cause nutrient malabsorption (lockout)...or is it primarily the lowering of ph (as a result of the salt accumulation)? A two step process.

Thanks for any opinions,
JD

So my question is: Do the nutrient salts themselves cause nutrient malabsorption (lockout)...or is it primarily the lowering of ph (as a result of the salt accumulation)? A two step process.

Look to the rootzone and examine your average rootlet, you will note these fine hairs that absorb a mixture of these salts in the soil mix, too much salts (N) (P) (K) ..around these rootlet hairs blocks the absorption process
for this reason you will often note me nagging noobies and oldies alike to flush the pot soil/dwc to either wash away the salt excess or even to disturb the lock up ...never be afraid to do it, as it happens in nature every time it rains.

I flush my plants every month and I do hate this choir, but it shows in the final result.....

Flush with 3 times the volume of the pot, with air temperate Ph neutral water, allow to recover in dim light, one day or overnight......avoid feeding for 2 weeks then resume at half the current rate only resume, when you see a positive improvement.

Hi Vostok,
I see you over at ICMag too. Same cool Avator. I'm DrDee over there...pretty new.

Thanks for the reply. So you're thinking it's actually a physical blockade sort of thing. That certainly could happen and makes sense.

I've been pondering this for awhile. One idea that's occurred to me is that there are certain paired nutrients that interact. An example would be an excess of Mg blocking Ca absorption. So no doubt, with overfeeding, there are at least a few paired nutrient interactions that occur. Individual nutrient lockouts.

The other issue I've been looking at is the high concentration of nutrient salts in the medium could cause an osmotic pressure away from the roots. This is an unfinished thought and I'm not sure how this would work.

The biggest point I'd like to discover is if a low PH always accompanies nutrient salt build-up. Or is both ph and ppm runoff testing necessary for an accurate diagnosis.
Cheers,
JD

from everything i've ever read, having the ph out of range is the reason for a plants inability to take in nutes. not allowing for run-off/not flushing, can cause a build-up of nutes in your medium. the build-up causes your ph to drop in your medium. after i add nutes to my rez, the ph always drops, every time. so i imagine this is what happens in the medium. i grow in coco now, but when i was in soil, i always allowed for a good bit of run-off, without soaking the soil. i always called this (in soil) a mini-flush, lol. at one time i did a feed/feed/flush routine, in soil. i decided to try the mini-flush thing, and it seemed to work well, so no more feed/feed/flush. at first i did the run-off ph testing thing. but after noticing no problems with the plants, i stopped. even if the r/o ph was off, i did nothing. unless the plants displayed some sort of issue, i never check r/o ph. you gotta figure, of course the r/o ph is gonna be off. you're washing out the build-up, that can naturally occur. i remember asking this question about medium ph years ago, over at natures cure. guy said that trying to get the same ph out, as you put in, is futile. he called it, "chasing ph." he said that if your plants aren't displaying any issues, who cares what the run-off ph is? i tend to agree... sorry for rambling, lol...

Hi Shaggy,
Ya, I agree that runoff ph isn't any kind of accurate measure, But I'm talking about plants that are showing problems. You know the routine...a noob posts a thread showing yellowing and odd patterned leaves and wants to know what deficiency it is. When it's actually a nutrient lockout. In those cases, runoff will at least provide qualitative if not quantitative info.

So what you're saying is that improper ph of nutrients causes an overall ph out of wack...then the plant can't absorb because of ph lockout and then the salts accumulate? I never considered that. Now it's become a chicken or the egg question...which came first?
Pondering my navel...
JD

JohnDee said:

Hi Shaggy,
Ya, I agree that runoff ph isn't any kind of accurate measure, But I'm talking about plants that are showing problems. You know the routine...a noob posts a thread showing yellowing and odd patterned leaves and wants to know what deficiency it is. When it's actually a nutrient lockout. In those cases, runoff will at least provide qualitative if not quantitative info.

So what you're saying is that improper ph of nutrients causes an overall ph out of wack...then the plant can't absorb because of ph lockout and then the salts accumulate? I never considered that. Now it's become a chicken or the egg question...which came first?
Pondering my navel...
JD

Click to expand...

ya, i agree, run-off ph can be important, if you let it, by not allowing for some way to wash out build-up. as i said, i'm in coco now, and i get loads of run-off, lol..

Silky,
I appreciated your mini-flush idea and might try suggesting that to some of the noobs in trouble that I run into. And coco, don't even mention coco. You must be aware that coco has somehow gotten a rep as OK for first timers. You wouldn't believe the trouble they get into. I may be calling on you as a coco expert! And indeed, lots of runoff with coco or there should be. Thanks for your opinions...
JD

This brings to mind the term root pressure.
There are salts in the plant that assist
in absorption.
When the salts are built up in the soil
they overpower the salts in the plant
So the plant can not pull.
Have I got that right?





**H@Ck ALLeRt**
Any info I give is based on what I would be comfortable doing.
Please get other opinions.

In nature plants don't live in plastic buckets but at my house they do or they get the f**k out.

I run coco too, drain to waste system with only like 10% run off if that....system is getting nice and dialed in. I do a feed/top off res with plain water/feed/plain water etc. Things are much better with clean water every now and again. Interesting topic im pulling up a seat.

Hey JD,

That is a great question you asked. I've never connected salt content with ph, so interesting to think about. I know in the case of toxic salt build up, it is a reverse osmosis issue where moisture is pulled from the plant because the soil salinity is higher than the root salinity. The first sign of it in cannabis is that downward curled leaf tip. I've read a bit about it but don't recall ever seeing ph linked to the issue. This article is a good laymen's explantaion: http://soiltesting.tamu.edu/publications/E-60.pdf

The article notes how it is common in nature for high salt soils to also have high ph. This seems counter to my experiences with nutrient mixes that often lower ph. So I don't know what this means in regards to a relationship between salt content and ph.

I hope someone can explain the relationship of overfeeding and nutrient lock out as well. I have seen it with my own eyes too many times, but never questioned the science of what is going on. Would be nice to understand this better.

Hi Guys,
I'm getting a little bogged down trying to understand the subtleties of your responses. I always tend to overcomplicate things though. lol

Charface and Bugeye...you guys both agree on the issue of osmosis moving water out of roots to rootzone...as an explanation of why nutrients get blocked.

Here's a link that agrees with your idea...

http://www.420magazine.com/forums/problems-pests-disease-control/86134-nutrient-lockout-how-avoid.html

Bugeye, you offer the downward cupped leaves as an example of this happening. But I've always thought that was more of an overwatering symptom. Also I see many overfed plants that are super dark green and exhibit deficiency symptoms that have no leaf cupping or limpness as you might expect from dehydration.

And why do some plants get toxic without the dark green coloration? My guess would be the rate of soil toxification. A sudden dump of nutrients would toxify soil with it not having time for much uptake.

I'm just voicing thought here...trying to fit some of this into my previous understanding. I'm afraid on the ph link, I may have fallen prey to a common forum occurence. You hear something spoken enough and you start believing it. I'm referring to toxic salt build-up and ph drop.

But I am learning things. Like the reason that there are ph ranges for certain nutrients. That occurs because out of those ranges, the nutrient salts re-combine and are unavailable for absorption. Only ionic forms can absorb. N+ can be absorbed, whereas NH4+ cannot until it's split up.

Bugeye...i'm still working on that article. It's mostly related to what occurs out in the open environment rather then container gardening, but the concepts are still valid and useful...just needing more thought to translate to our purpose. Great info though and thanks.

Hi Fishindog...coco guys have a slightly different set of variables but overfeeding certainly can occur. Let me ask you a question. Was there any one thing that clicked for you to make coco work? So many noobs are using it and getting into trouble.

Cheers guys,
JD

Ill check this out in a bit.
thanks for the link


**H@Ck ALLeRt**
Any info I give is based on what I would be comfortable doing.
Please get other opinions.

In nature plants don't live in plastic buckets but at my house they do or they get the f**k out.

JohnDee said:

Silky,
I appreciated your mini-flush idea and might try suggesting that to some of the noobs in trouble that I run into. And coco, don't even mention coco. You must be aware that coco has somehow gotten a rep as OK for first timers. You wouldn't believe the trouble they get into. I may be calling on you as a coco expert! And indeed, lots of runoff with coco or there should be. Thanks for your opinions...
JD

Click to expand...

(very uncomfortable with the "expert" thing, i prefer experienced lol.) personally, i think new growers are just better off starting in soil, more forgiving. things happen quickly in hydro, and you gotta be ready to respond quickly.

A leaf structure where there is a gentle curve all the way from the back to the front is indicative of overwatering, especially if the container is heavy. A leaf structure that is relatively flat with a sharp down curved hook near the tips is indicative of over-feeding and salt levels starting to get too high. These are just indications, not absolutes, so just a starting point when I evaluate what is going on.

It seems to me also that there is more to over-feeding than just the reverse osmosis from salt levels being too high. Perhaps a better question is, can you lock out nutrients from over feeding even if the ph is in range and salt levels are not at toxic level?

Thanks for that leaf description Bugeye...
And I agree, the osmosis thing can't be the whole picture. One thing I've been pondering is how paired nutrient interactions enter into this (ion-ion interaction). Nutrients are carried through the cell wall by facilitated diffusion and often, more then one ion used the same protein channel. Too much of one will block the other. I believe Ca and Mg work this way. So early on, in an overfeeding situation, you might see only one deficiency yet still...the cause could be a single ion excess blocking it's pair. No true toxic salt build up and probably a normal ph. Make sense?

Here's an excellent webpage on mineral nutrient uptake

http://plantcellbiology.masters.grkraj.org/html/Plant_Cellular_Physiology4-Absorption_Of_Mineral_Nutrients.htm

Cheers,
JD

Excellent link, thank you. I'll be busy digesting it for awhile!

In over my head. lol



**H@Ck ALLeRt**
Any info I give is based on what I would be comfortable doing.
Please get other opinions.

In nature plants don't live in plastic buckets but at my house they do or they get the f**k out.

Foilar Feed and you NEVER get burnt plants ...lol, add half teaspoon(max) to a pint spray bottle, fill with warm water shake and spray 1x time per day

Thanks for sharing your knowledge everyone. This thread is over my head too but the elements I understand are very helpful.

Vostok, I am becoming more of a convert to foliar feeding. It is amazing how fast a plant will green up and clear deficiency symptoms with a dilute foliar feed (I am using 1/8 strength).

The term "antagonism" was new to me in your linked article, JD. I'll have to write it down in my notebook to remember it. But if you google "nutrient antagonism charts" you get the info I've always wanted to have but didn't know the search term to find. Here is an example of one that took me back to rollitup (see 3rd post): https://www.rollitup.org/marijuana-plant-problems/651462-crazy-plant-flesh-eating-disease.html

So thanks again for an excellent afternoon, I learned a lot!