Struggling with low rootzone pH...

[ChebbyFlowers]

Hi there everyone,

I've got 6 plants in first week/transition into flower. I've grown them out larger than I normally do. Five of them are doing fabulous, but one just seems to keep having issues with Calcium/Magnesium deficiency. I'm getting speckles on some of the leaves and lower leaves get splotches that get brown and necrotic and begin to die.

This started happening a couple weeks ago and I initially thought that I was not feeding consistently enough. The plants are all in CocoLoco mix which is supposed to have enough nutrition to last several weeks so I was feeding salts sparingly and just doing pH adjusted water with some CalMag mostly.

After I noticed the deficiencies I began just feeding on a schedule. Every other day I would feed at an EC of about 1.00-1.10. The medium would dry back well enough, but it wouldn't be totally dry. This seemed to fix the issue and I went ahead and did a slurry test on the plant in question as well as another couple. The pH of the one in question seemed a bit low, around 5.3... the others were closer to 5.9.

I started keeping the feed water pH a bit higher between 6.3 and 6.5 and thought that this would definitely fix the issue. The plant has been stretching nicely and the new growth looks healthy, but today I noticed some more speckling on the interior leaves as well as more necrosis on the lower leaves. I decided it would be a good time to flush this plants medium with pH adjusted water.

I ran 5 gallons of water through it and then replenished nutrients with another 2.5 gallons of feed solution. Here's where I am confused: my feed solution was 1.1 EC at 6.5 pH....I checked my runoff to make sure I wasn't teaching a lot of salt and as I suspected it was pretty clean, .9 EC, however the runoff pH was all the way down to 5.1-5.2. Even after leaching whatever salt buildup, if any, how can this pH be so low? Should I be concerned about this or just try and let the plant be and continue to monitor it?

If I am treating the CocoLoco more like a hydro medium at this point I know the pH should be between 5.5 and 6.5 and this has always worked for me in past grows, but as I said I always kept plants much smaller, in smaller containers. These girls are all in 7 gallon plastic pots. I'm used to 3 gal. root mass and plants about 2' tall at harvest. These girls are already almost 2.5' tall and only just started stretching.

Really I guess my question is how low a soil pH is too low when growing in Coco? If you're feeding salt based ferts in "soil" what makes that any different of an approach than coco other than how long the heavier media takes to dry back?

 

[ChebbyFlowers]

Here are some photos of the affected plant as well as the whole grow.

 

[ChebbyFlowers]

Bump?

 

[ChebbyFlowers]

Still hoping someone has some input. I watered the girls with Recharge tea this morning. They all seem happy so I do think I may be chasing my tail with this. I'm gonna try and check the root condition of the one plant tomorrow and report back here.

Anybody have any idea why the runoff pH would be dropping if it isn't rot?

 

[Thatoneguyyouknow_]

You are giving them food faster then they are consuming it, and this is causing a soil acidity that goes a little deeper every feeding, and is likely why your PH is trending downward. Every time you water til drainage, the residual salts are flushing out (but not fully) and summed on top of the measurements of the nutrient solution going in. There is something acidic in your regiment you are giving faster then the plant can consume it basically.

Flush with PH neutral water, then refeed at prob 10-15% your current feed tds/ec and intended pH. Keep tabs on drainage, if the trend continues, cut another 10-15% off the tds.

The damage on your leaves is a calcium lockout caused by the acidic trend in the soil. Calcium is the first element to lock out with an acidic trend, Magnesium will follow, and then potassium IIRC

 

[ChebbyFlowers]

You are giving them food faster then they are consuming it, and this is causing a soil acidity that goes a little deeper every feeding, and is likely why your PH is trending downward. Every time you water til drainage, the residual salts are flushing out and summed on top of the measurements of the nutrient solution going in.

Flush with PH neutral water, then refeed at prob 10-15% the tds/EC you were running for feed before. Keep tabs on drainage, if the trend continues, cut another 10-15% off the tds.

The damage on your leaves is a calcium lockout caused by the acidic trend in the soil. Calcium is the first element to lock out with an acidic trend, Magnesium will follow, and then potassium IIRC

So even though I am feeding at a pretty low EC of .9 - 1, you think I am overfeeding? Should I be giving plain water in between feeds, or feed every time? I am used to an inert coco/perlite mix, but this is kind of a hybrid mix, the Coco Loco by Foxfarm...

I am aware that the damage is a calcium issue, my main concern is the pH drop. I know once I fix the root of this issue the calcium lockout would resolve.

I did flush the medium significantly and the runoff was coming out very low, so I figured that was sufficient, but the pH is still low. If there was still salt buildup wouldn't the runoff EC suggest this with a HIGHER reading rather than a low one?

 

[Thatoneguyyouknow_]

So even though I am feeding at a pretty low EC of .9 - 1, you think I am overfeeding? Should I be giving plain water in between feeds, or feed every time? I am used to an inert coco/perlite mix, but this is kind of a hybrid mix, the Coco Loco by Foxfarm...

I am aware that the damage is a calcium issue, my main concern is the pH drop. I know once I fix the root of this issue the calcium lockout would resolve.

I did flush the medium significantly and the runoff was coming out very low, so I figured that was sufficient, but the pH is still low. If there was still salt buildup wouldn't the runoff EC suggest this with a HIGHER reading rather than a low one?

Oh yea, definitely over feeding then. Just not enough to cause burn. You need to flush until the drainage is the same, or very close to the same as the input ph, or you didnt actually flush fully lol. and wait til the next dry cycle is done so you dont cause any rot btw. In a 3 gallons pot, you may need up to 6-8 gallons for a real flush.

If you are feeding every watering you need to be at like 350ppm/0.6 in soil. If you move to peat/perlite, or coco you can get by up to about 600 with most strains.

Im feeding every watering for consistency sake rn, and im running it between 300 and 350.


Most growers feed high, then water a couple times, then feed high again.

 

[Thatoneguyyouknow_]

after the flush, immediately re feed with a ph'd nutrient solution at like 350ppm. Like as soon as the pots done draining the last of the flush water. And if you feed every watering dont go above that unless you know for SURE your plant can take it. Always error toward caution

 

[ChebbyFlowers]

Oh yea, definitely over feeding then. Just not enough to cause burn. You need to flush until the drainage is the same, or very close to the same as the input ph, or you didnt actually flush fully lol. and wait til the next dry cycle is done so you dont cause any rot btw. In a 3 gallons pot, you may need up to 6-8 gallons for a real flush.

If you are feeding every watering you need to be at like 350ppm/0.6 in soil. If you move to peat/perlite, or coco you can get by up to about 600 with most strains.

Im feeding every watering for consistency sake rn, and im running it between 300 and 350.


Most growers feed high, then water a couple times, then feed high again.

Well technically it is a coco/soilless medium, so I'm pretty close with the EC. So just so I'm understanding why exactly you think I'm overfeeding, is it because of the strength/EC of my feeding, or more so the frequency?

I too like the consistency of feeding every watering as I feel this is just more stable for the root zone. You think cutting my feed strength down to around .6 EC would be sufficient?

 

[Thatoneguyyouknow_]

Because each feeding the drainage comes out higher EC and lower ph then the previous watering right? Tat means that the plants is pulling moisture from the substrate faster then it is pulling the nutrients. In specifically coco and DWC this is very common.

When you water the next time, its not enough volume to fully push the previous leftover nutrients out of the substrate.

Those nutrients left behind, which are acidic salts, combine with the ec of the next feeding, driving it's ph down, preventing the plants from absorbing nutrient even more, making the problem worse every time it happens, and creating a cycle.

Thats just how it works lol.

 

[Thatoneguyyouknow_]

you should be feeding at 5.8-6.3 in straight coco or soiless as well. You are technically growing hydroponically going soiless substrate

Feeding at 6.5 is probably what was initially making her feed slow, before that created an acidification cycle because the nutes are acidic..

 

[Thatoneguyyouknow_]

Fun fact:

The reason calcium is the first lockout deficiency to show so fast, is because when calcium swings acidic, it will automatically change state of calcium, to a salt that is unusable by plants.

This locks calcium out of the roots because calcium hcl cant be absorbed by them, but it also turns the calcium already in the leaves to a salt too, physically scarring the tissue unrecoverably.

 

[ChebbyFlowers]

you should be feeding at 5.8-6.3 in straight coco as well. You are technically growing hydroponically using coco.

Feeding at 6.5 is probably what was initially making her feed slow, before that created an acidification cycle because the nutes are acidic..

That all jives with what I had previously learned, I guess where I've confused myself is trying to adopt a soil growers mindset because the Coco Loco is pre amended with stuff. I began the grow just giving them water then ran into Calcium issues so I started feeding heavy and that seemed to fix the issue for a while. Makes sense tho that now I have a salt problem causing the same issue. I think either way most of the nutrition that was loaded into the medium from the get go has probably been consumed, so I SHOULD be treating it more like hydro now right? -Of course with lower EC feeding and lower pH to promote uptake-

 

[ChebbyFlowers]

Fun fact:

The reason calcium is the first lockout deficiency to show so fast, is because when calcium swings acidic, it will automatically change state of calcium, to a salt that is unusable by plants.

This locks calcium out of the roots because calcium hcl cant be absorbed by them, but it also turns the calcium already in the leaves to a salt too, physically scarring the tissue unrecoverably.

That is fascinating. I am always so analytical with this stuff so this is great info! And I am appreciative of your detailed responses, thank you for putting some thought into my issues!

 

[Thatoneguyyouknow_]

That all jives with what I had previously learned, I guess where I've confused myself is trying to adopt a soil growers mindset because the Coco Loco is pre amended with stuff. I began the grow just giving them water then ran into Calcium issues so I started feeding heavy and that seemed to fix the issue for a while. Makes sense tho that now I have a salt problem causing the same issue. I think either way most of the nutrition that was loaded into the medium from the get go has probably been consumed, so I SHOULD be treating it more like hydro now right? -Of course with lower EC feeding and lower pH to promote uptake-

thats actually hard to answer. i use a good bit of coir and peat in my mixes, but i always treat them as soil PH wise even if plants have been in there a long time. Even if the coir is only 20% soil mixed in, id still treat it as soil.


I have no idea what the parts and ratios of your soil is though, so im not actually going to answer that question in a specific way lmao.

 

[ChebbyFlowers]

thats actually hard to answer. i use a good bit of coir and peat in my mixes, but i always treat them as soil PH wise even if plants have been in there a long time. Even if the coir is only 20% soil mixed in, id still treat it as soil.


I have no idea what the parts and ratios of your soil is though, so im not actually going to answer that question in a specific way lmao.

I guess that's what confuses me....what do you mean treat it like soil? Other than a slightly higher pH, what difference is there in treatment? Longer dry-back? (But isn't this more just because it takes longer to dry and holds less O2?)
Less frequent feeding, no runoff?
That's the way I understood it, but hesitate to let the medium get too dry because I learned to grow in coco, keeping it pretty moist always.

 

[Thatoneguyyouknow_]

I guess that's what confuses me....what do you mean treat it like soil? Other than a slightly higher pH, what difference is there in treatment? Longer dry-back? (But isn't this more just because it takes longer to dry and holds less O2?)
Less frequent feeding, no runoff?
That's the way I understood it, but hesitate to let the medium get too dry because I learned to grow in coco, keeping it pretty moist always.

i was mainly just meaning PH wise. I water til drainage in soil, but not much drainage, and like 40%+ of my mix is perlite so i an have a more rapid dry cycle, I water every day in my current mix pretty much, and always hovering around 300ppm feed (most) every watering.

I still run my ph6.5-6.8 anywhere in there. I dont chase specific numbers with it, just a specific range.

Even with all the perlite, peat, and coir in my mixes, there is still an amount of screened potting soil. So i still treat the entire mix like soil ph wise.

Id recommend a feed water water kind of cycle in soil to most people. Even though that's not what i do personally lol.

 

[Thatoneguyyouknow_]

im just giving information as opposed to an answer here because thats a very difficult question to answer if i dont know exactly what is in that particular mix. (really it's an impossible to answer question lmao) And i dont really have a way to explain the ec reading along side the acidic drainage ph.

Al i know for sure, is you have some early nute burn signs going on and soil is beginning to acidify causing your cal deficiency, which is an symptom of the other over feeding being present but minor for an extended period. How high is your PK in your current ratio? no signs of N tox.

 

[ChebbyFlowers]

im just giving information as opposed to an answer here because thats a very difficult question to answer if i dont know exactly what is in that particular mix. (really it's an impossible to answer question lmao) And i dont really have a way to explain the ec reading along side the acidic drainage ph.

Al i know for sure, is you have some early nute burn, and overfeeding, and lockout symptoms going on and soil is beginning to acidify, which is an symptom of the other problems being present but minor for an extended period. How high is your PK in your current ratio? no signs of N tox.

Oh I absolutely understand it's hard to give solid answers with this stuff, especially through text and photos... It really seems you like to grow in a similar fashion to the way I am used to as well. I think I will try and flush the one plant again once it dries out again and back off on feed strength. I will also begin lowering input pH and letting it range like I am used to.
I don't know exact ratio of P and K right now. I'm using equal parts Micro, Grow, Bloom of the GH Flora series. Was adding a low dose of Silica and CalMag to each feed and then 2.5ml/gal of each of the Flora. I really didn't think I was pushing it at all. Every other grow I've done I have employed that same feed ratio for the stage of growth my plants are currently in. They are just starting to bud and probably have another week or so of stretching to do. I'll probably back off the FloraGro by half over the next few days and then drop it entirely after stretch is complete.