Have a new discoloration just popped up in the last 3 days, have not experienced this before, narrowed down to a couple things. Looking for other opinions please and thank you.
Info: 2 plants in a 2x4, about 26/27 days since flip. A mix of FF soils w perlite. Using FF trio and cal-mag. Ph inputs are always 6.3 - 6.5 (using distilled water base). Temps 75-82, humidity at 35-40 with lights on @ 55 lights off.
Mid/lower growth, the plant on the right.
It could be a phosphorus deficiency, but is is it getting blocked by a ph imbalance. What is the ph from your run off?
Just checked twice and run off ph is at 5.7 @Mrgreenthumb. Thinking back 3 days the only thing i have done differently is having to use more ph up after mixing nutes for the last feeding.
Looks like the same thing that killed my west row I.B last year. Mine was lock out from PH imbalance.
5.7 is a bit low for soil, you are going to want to get that up to 6.5 would be nice.
Yea @ColeLennon 5.7 is going to cause issues, for sure in soil
Is it one plant or all of them? Mine was a single plant the had drastic shift in PH and lock out due to not drying off. I kept feeding more P and flushing 4 weeks later I chopped it. If it happens again. I will stop and fix the PH problem and dry off. That was in Coco/Peat/Perlite. Soil is tougher.
Ive only got two in there and its only looking like one of them. In the first pick its on the right, kind of in the middle center right, mid way up the plant. Have others outside and clones that seem to be fine.
I would rotate the plant towards the outside of the bunch. Fix your Ph issue to 6.5 with a balanced “micro” dose of light nutrients and “leave it alone to dry off”. That later part is how I killed mine.
The original 1 gallon was happy frog/perlite they got up potted to a 5 gallon about a week before flip so 4/5 weeks ago was a happyfrog/strawberry fields/perlite mix. They get wattered every 2/3 days with a feed every every 3rd water. They get pretty dry in 3 days with the coco and perlite. Relative humidity here is crazy low.
I dont watter to much run off only till it starts dripping from the bottom of the fabric pot. Maybe i should when i do. These have never been flushed.
I added microbe brew 2nd time this grow with the last feed as well, maybe something there was off.
I would start by fixing PH and rotating the plant to the outside of the bunch. Hope for the best. 
When I have a fluctuation like that in ph I make sure to re calibrate my ph pen properly. I had a similar problem once and ph pen was way off.
That is really good point. So easy for us stoners to put this off. I just keep mine sitting in skinny cup of 7.0 calibration fluid. My cheap vivosun still reads low. 6.60 when its 7.0. “have to keep that back of mind” I only use it when I’m bumpin nutrients.
Just ordered fresh calibration fluid. I always use the drops as a secondary verification and f the colors in range of my reading i call it good. I gave a watering with about 10% runoff with 6.5 water yesterday. Will get a balanced nutes feeding in tomorrow afternoon. The 5 gallon pots are pretty dry in 2 -2 1/2 days, by 3 the plants wilt. Concerened more now since i have a 5 day business trip, leaving saturday. My wife can water for me but beyond that she really doesnt know what to look for or adjust.
Ya know, this is something I’ve been plagued with for years over different mediums, feeds, houses and so on. Not this exact problem, but this exact timing. There is something that happens to plants at week 4-5. I swear, without fail, I’ll always run into issues at this point. I have a journal that goes back quite a few years and it’s incredible how many plants I’ve had that have an issue at this far into flower.
I’ve tried just about everything to be honest. I’ve tried different strength nutrients, veg versus flowering nutrients, pH and everything.
There’s quite a bit to this. First, the P requirements for a plant are really really low. There’s quite a few research studies that quote something like 60-90 ppm for P throughout flower. K is acceptable anywhere from 60-300 ppm. To have a real P or K deficiency should be relatively rare. I’ve had the best results with a 3-1-2 throughout flower, only encountering a nitrogen deficiency at around week 4-5.
To be honest, I’m unsure of whether or not I’ve actually grown a plant past this point without some sort of senescence. I ran Thai stick for a while and it was seemingly incurable to encounter issues at this point. At one point, I put one in at 16 ml/gal and week 4-5 it showed nitrogen so I upped the feed. Next cut of the same plant going in I started at 20 ml/gal and at week 4-5 it showed the same thing. This last one I did went in at 24 ml/gal and literally still showed the same nitrogen deficiency at week 4-5. It just seems like an endless sink for nitrogen or something. It seems like the more nitrogen in veg I’d give it, the more hungry it’d be when it hit flowering.
Nutrition for cannabis has been one of my most recent topics I have committed to researching. There’s quite a few scholarly articles out there going through the needs of plants. Out of all of them, the most prevalent finding is that there should be 160-190 ppm of Nitrogen throughout flower. Secondly, the P and K values are much lower than what normal bloom nutrients give. It boils down to a 20-10-20 feed being the best ratio for inflorescence yield at 160-190 ppm nitrogen. Granted, different plants command different feeds.
At this point, I take everything in stride. Losing a few leaves won’t be the worst. I’d love to grow a plant and never lose a leaf. It does take quite a while to properly find exactly what kind of feeds a plant wants. Take a clone and get it ready for the next cycle. Keep a journal!
This is when i run into issues the last few grows too. Different strains, photos and autos. I typically veg for 5/6 weeks or so plants are beautiful lush green and by 3/4 weeks flower it hits. I continue to use veg nute ratios until 7-10 days after flip before converting to suggested bloom ratios.
I also wonder if the ph up/down solution builds in the soil over time driving ph in the substrate/medium. For me it would be down since the water used is initially pretty alkaline @ 7-8 and ph down added with every water to get it to 6.3-6.5. Could explain the 5.7 runoff and subsequent lock out.
My problems don’t ever come from pH up or down. I actually don’t ever check or adjust the pH of any of my solutions anymore.
I think it’s easy to point at pH as the catch-all of issues but I have had remarkably better experience without worrying about it. I’ve had all kinds of meters including quite a few that I built from the ground up with microcontrollers. Even with expensive probes and automated dosing systems, it never solved the issues I’ve always had. I’ve found scholarly articles and book mentions of bigger ranges of pH than the cannabis community accepts.
I feel like the NPK ratio and dosage is by far the most important. I’ve found quite a few research articles about the NPK ratios for cannabis through flower. I want to say around 3-4 of them all kind of conclude on this benchmark of 160-190 ppm N. I want to say ~70 ppm P and a ridiculously large range of 60-350 ppm K are suggested too.
I’ve stopped using bloom nutrients altogether. Plants tend to look really healthy up until the 4-5 week mark then I usually start losing some more mature leaves. Sometimes I wonder if cannabis just does that. Seems like most plants I see on the internet have some sort of leaf drop. It’s WAY common to see indoor plants with problems online.
