Calcium Magnesium Lockout

Week4@inCharge

Week4@inCharge

Well-Known Member
Hey guys, little stumped at what's been going on with all my grows so far like clockwork. I know how to remedy it, but am befuddled as to why at about week 3-4 of flower, the cannabis plant wants to lower the soils pH to 5.8? That's right outside (according to the cannabis pH charts)of the Calcium and Magnesium preference of 6.3-6.5pH. So why does the Cannabis plant drop the pH? My tap charcoaled filtered waters pH is 8.3. So the first signs on this last grow (from a clone) I spotted some leaves curling up fast at the bottom and a few leaves with rust spots (that do not rub off when touched) Everything is super healthy so far and glad I was able to pick up on the early signs here and checked the pH of the soil to find the 5.8 reading. My go to is Dolomite Limestone. That brings the pH up to where the calcium and magnesium like to be. But....I wonder what the plant is looking for here. In organics... whenever the plant is in need, the root system changes the pH to get that need from the soil. So what is that need that's at 5.8? I don't see anything from the Cannabis Soil pH Charts that it can use at 5.8..
 
Week4@inCharge said:
Hey guys, little stumped at what's been going on with all my grows so far like clockwork. I know how to remedy it, but am befuddled as to why at about week 3-4 of flower, the cannabis plant wants to lower the soils pH to 5.8? That's right outside (according to the cannabis pH charts)of the Calcium and Magnesium preference of 6.3-6.5pH. So why does the Cannabis plant drop the pH? My tap charcoaled filtered waters pH is 8.3. So the first signs on this last grow (from a clone) I spotted some leaves curling up fast at the bottom and a few leaves with rust spots (that do not rub off when touched) Everything is super healthy so far and glad I was able to pick up on the early signs here and checked the pH of the soil to find the 5.8 reading. My go to is Dolomite Limestone. That brings the pH up to where the calcium and magnesium like to be. But....I wonder what the plant is looking for here. In organics... whenever the plant is in need, the root system changes the pH to get that need from the soil. So what is that need that's at 5.8? I don't see anything from the Cannabis Soil pH Charts that it can use at 5.8..
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How are you reading your soil for ph? Based on runoff or are you taking some soil and making a slurry? You should do some research on DLI. It’s very common for issues to arise at that 3-4 weeks into flower. Usually related to nutrients as the plant gets less light it can start using less nutrients. I’m not a big soil guy but in coco I just make sure to get extra runoff to keep from any salt buildup right after I flip to 12/12.
 
SofaKingHigh_ said:
How are you reading your soil for ph? Based on runoff or are you taking some soil and making a slurry? You should do some research on DLI. It’s very common for issues to arise at that 3-4 weeks into flower. Usually related to nutrients as the plant gets less light it can start using less nutrients. I’m not a big soil guy but in coco I just make sure to get extra runoff to keep from any salt buildup right after I flip to 12/12.
Click to expand...
thanks, Im using a digital pH pen to check the soils pH. I don't think it's nutrients as I've amended the soil few weeks ago with bloom specific organic matter. The plant looks otherwise In great health. I'm just recognizing these early signs easier.
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Does your soil have any bark mulch in it?... The soil I use does. Starts out fine in veg, then suddenly, the PH will crash. This is a result of the bark mulch decomposing and turning acidic. I have to do hard PH corrections to fix it, and I only have to do it once. After that, my well water at 7.3 is good till the finish. Pain in the ass, but remember also that Ca is very antagonistic with many other nutrients. I quit using Cal Mag altogether as my well water is Ca ready, and some of the nutes I use have plenty of Mg. So, .. that's $59 bucks a gallon I don't use anymore.
 
DoubleAtotheRON said:
Does your soil have any bark mulch in it?... The soil I use does. Starts out fine in veg, then suddenly, the PH will crash. This is a result of the bark mulch decomposing and turning acidic. I have to do hard PH corrections to fix it, and I only have to do it once. After that, my well water at 7.3 is good till the finish. Pain in the ass, but remember also that Ca is very antagonistic with many other nutrients. I quit using Cal Mag altogether as my well water is Ca ready, and some of the nutes I use have plenty of Mg. So, .. that's $59 bucks a gallon I don't use anymore.
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You don't have the microbes that will buffer the pH like people doing full on organics though.
 
DoubleAtotheRON said:
OP... Disregard our antics.. just something we do on a thread every couple of days... it'll be over in a couple of minutes.
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I know... I catch on sometimes..lol. You guys are a riot. :D I'm using Happy Frog which is 50% peat moss, an acidic Inert media. Which has me Wondering...is it really soil? The one thing I haven't really placed close attention to that seems to be the most controversial topic known to the cannabis culture.....is VPD. So I'm thinking of mixing some (mushroom?) compost in the soil/media next grow when I redo the soil mix to make it more of a "soil" than an inert media. As much as I don't like the peat moss I do see the benefits of it.
 
Week4@inCharge said:
I know... I catch on sometimes..lol. You guys are a riot. :D I'm using Happy Frog which is 50% peat moss, an acidic Inert media. Which has me Wondering...is it really soil? The one thing I haven't really placed close attention to that seems to be the most controversial topic known to the cannabis culture.....is VPD. So I'm thinking of mixing some (mushroom?) compost in the soil/media next grow when I redo the soil mix to make it more of a "soil" than an inert media. As much as I don't like the peat moss I do see the benefits of it.
Click to expand...
I use C25 (not a well known soil), but it's peat based with perlite, vermiculite, and bark mulch. I love the way it drains, but the ph correction is not that big of a deal. It's cheap, and works well. It's basically a non amended soil.. like a clean slate. Just my preference.
 
@Week4@inCharge , the only thing that bugs me, is that when I follow VPD in this soil, it transpires so fast, that Im finding that I need a bigger dehuyey. They get in the zone, and all the sudden I have to feed 40 out of like 87, and they transpire so fast that I can't keep up with the RH... it gets out of control in late flower. Im currently looking for a Quest 255 or 225 Dual. Tired of fighting this RH at this stage. I wished they weren't so damn expensive.
 
DoubleAtotheRON said:
I use C25 (not a well known soil), but it's peat based with perlite, vermiculite, and bark mulch. I love the way it drains, but the ph correction is not that big of a deal. It's cheap, and works well. It's basically a non amended soil.. like a clean slate. Just my preference.
Click to expand...
looked that one up real quick... 25% peat moss.. sounds like something I might want to try (or similar)
 
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