Photoperiod K Deficiency???

[beachbuds]

-MOAB hybrid strain, week 6 of flower. She’s a 10 week finisher.
-Super soil grow using sub cools recipe (swapping OF for Roots in e recipe) in 15gal fiber pot.
-blumat system, water only straight from dehuey condensate(2ppm so pH not reliable). Just water, no cal mag
-4 Autocobs in a 4x4 on 12/12, 16” away
-rH ranges 52-45 each day
-temp is 19-26c

thought it was light burn at first but seems to have progressed across the plant over the last 10 days after reducing PPFD. Those multiple leaves are from are thiughta. see pics below. The side by side leaf pic is comparing a clone of this mama grown in 3x3 tent next door. 2 Autocobs and a spider farmer 1000 lighting that grow. Water source, RH, temp basically identical.

the burnt leaf margins, tip yellowing, long purple petioles makes me think potassium. also wondering if it’s combo deficiencies due to 15 gal pot of super soul not being enough to fuel that plant for the whole grow.

Thoughs?

 

[Builder0101]

Good guess. I have the same thing on one of my plants. I addressed the K but did not seem to improve or worsen. Fimulvic spray greener her up pretty well. You may try adding Humic and Fulvic acid. They will chelating the existing K in the medium and make it more available w/o risk of burn. I personally don't like dehu water. Pathogens can colonize it. IMO.

 

[Kinezokyprios]

I am certain your medium is rich in all required nutrients. You need to add humic and fulvic acids to make all this food "eatable".

 

[Builder0101]

Yep. I'd try the humic/fulvuc 1st. Sorry for all of the crazy typos in 1st reply. Fulvic spraywill probably green her up a little.

 

[beachbuds]

Thanks @Builder0101 and @Kinezokyprios! Appreciate the guidance. I shut off the blumats for a few days then doused a tea of earthworm casings, molasses, kelp meal and tiny little shot of fish emulsion (holy crap that stuff stinks!). No real change, but it’s been only a few days. I understand unsulphured blackstrap molasses is a chelator as well as a good source of K (1:1:5 or so I’ve read) so I was planning on keeping that going in all subsequent waterings. Little hesitant to do any foliar at this point given I’m in week 6 of flower so are you suggesting a very targeted foliar on just the yellowing leaves? Also any ranges And application suggestions for the amounts of humic and fulvic acid? I did add a little humic acid in the original super soil mix but it was only 1 tsp for 40 gallons so...?

Another thought I had on this yellowing thing was simple overwatering from my blumats. It didn’t seem like the soil was overwhelming wet and I didn’t experience any flooding, however I was steadily increasing the water drip during weeks 2-4 of flower and was going through a solid 2 gallons a day before I went into infirmary mode snfnshut it off. Don’t know if that’s a cause however it’s another possibility in the realm of reason I suppose.

Re: the dehuey condensate, I went back and forth on that one so I totally understand your comment. However given the ultra low ppm and the fact that my dehuey is only about 4 months old, I’m not overly concerned about pathogens at this point. Read a number of articles and forum posts on this and it seems like another one of those topics where anectodal stories and strong opinions drive people’s decisions. Would love to see a research paper or other peer-reviewed study that detailed the pathogens that could be found in condensates and the risks associated with them. I’m generating 5 gallons every 3 days and it’s a shame to not utilize such a low ppm water source.

 

[Kinezokyprios]

The leaves that already showed the problem will not get well. This is why you don't see immediate improvement. The aim is that the problem will not continue further on the rest. When leaves showed the problem it was already late to respond anyhow. While you gave the humic/fulvic supplements, you must continue with your normal feeding schedule. They need a low but steady supply of food. About foliar sprays, I am personally against them on cannabis. What the plants get through soil might take more time to work but is more than enough. There is no magic or ideal dose for any supplement, only trial and error. Your watering seems to be fine. Cannabis has to be "thirsty" for our desired outcome.

 

[Kinezokyprios]

I tend to ignore pathogens since my experience in guerilla grows has shown that you cannot avoid them but the plants after a certain stage of development can cope adequately with them plus cannabis is a short time crop, so no time to respond effectively. You should worry more about pests like bugs and fungi transmitted by them, not pathogens through water.

 

[Builder0101]

The leaves that already showed the problem will not get well. This is why you don't see immediate improvement. The aim is that the problem will not continue further on the rest. When leaves showed the problem it was already late to respond anyhow. While you gave the humic/fulvic supplements, you must continue with your normal feeding schedule. They need a low but steady supply of food. About foliar sprays, I am personally against them on cannabis. What the plants get through soil might take more time to work but is more than enough. There is no magic or ideal dose for any supplement, only trial and error. Your watering seems to be fine. Cannabis has to be "thirsty" for our desired outcome.

I agree. Foliar feeding later in flower requires care. Make sure your humidity is low, lights on and air movement is good. Do not spray the flowers. Folic acid can supplement light. Funny how that works. I had great success greening up my leaves with folic. That said the plants need to ultimately get their nutrients from a well balanced soil.

 

[Builder0101]

Thanks @Builder0101 and @Kinezokyprios! Appreciate the guidance. I shut off the blumats for a few days then doused a tea of earthworm casings, molasses, kelp meal and tiny little shot of fish emulsion (holy crap that stuff stinks!). No real change, but it’s been only a few days. I understand unsulphured blackstrap molasses is a chelator as well as a good source of K (1:1:5 or so I’ve read) so I was planning on keeping that going in all subsequent waterings. Little hesitant to do any foliar at this point given I’m in week 6 of flower so are you suggesting a very targeted foliar on just the yellowing leaves? Also any ranges And application suggestions for the amounts of humic and fulvic acid? I did add a little humic acid in the original super soil mix but it was only 1 tsp for 40 gallons so...?

Another thought I had on this yellowing thing was simple overwatering from my blumats. It didn’t seem like the soil was overwhelming wet and I didn’t experience any flooding, however I was steadily increasing the water drip during weeks 2-4 of flower and was going through a solid 2 gallons a day before I went into infirmary mode snfnshut it off. Don’t know if that’s a cause however it’s another possibility in the realm of reason I suppose.

Re: the dehuey condensate, I went back and forth on that one so I totally understand your comment. However given the ultra low ppm and the fact that my dehuey is only about 4 months old, I’m not overly concerned about pathogens at this point. Read a number of articles and forum posts on this and it seems like another one of those topics where anectodal stories and strong opinions drive people’s decisions. Would love to see a research paper or other peer-reviewed study that detailed the pathogens that could be found in condensates and the risks associated with them. I’m generating 5 gallons every 3 days and it’s a shame to not utilize such a low ppm water source.

The molasses is a good idea for watering. Less is more in my opinion. A teaspoon per gallon. It feeds the microbes among other things. The humic and fulvic should be according to the directions or 1/2 dose. Manufacturers want you to use up the product and buy again. I also believe good clean water is very effective when used in conjunction with additives to water. Dont want to clog the roots with too much stuff. As your plants near maturity they will drink less so backing off on the water (listening to your plants is crucial)
Also less water late in flower, as long as the plants are getting what they need, can only help keep the humidity down. I'm not overly concerned about pathogens in condensate water. Just one variable to consider. If your plants are healthy as well as your microbial population it is even less of a concern.

 

[beachbuds]

Thanks again for all the support. I found this publication from 2019 that covers humic acid supplementation.

Impact of N, P, K, and Humic Acid Supplementation on the Chemical Profile of Medical Cannabis (Cannabis sativa L)

Mineral nutrition is a major factor affecting plant growth and function. Increasing evidence supports the involvement of macro and micronutrients in secondary metabolism. The use of the appropriate nutritional measures including organic fertilizers, supplements, and biostimulants is therefore a...

www.frontiersin.org

Interestingly, the authors found that humic acid supplementation actually reduced THC and CBD at the top of the plants. From the paper:

“HA was found to reduce the natural spatial variability of all of the cannabinoids studied. However, the increased uniformity came at the expense of the higher levels of cannabinoids at the top of the plants, THC and CBD were reduced by 37 and 39%, respectively. Changes in mineral composition were observed in specific areas of the plants”.
There is still so much to learn!