Looks like a phosphate uptake issue but I can not figure it out

[WeedsInMyMind]

Background. I have grown for quite a few years at this point. I learn something new every year though in this hobby, and I am hopeful that one of you can help me figure this out because I am flat out stumped. As you can tell from the attached pics it appears to be a phospate issue with the purple stems, purple spotting, yellow on the edges and with the big fan leaves you can see the curl. Here are the Cliff notes:

Soil - mix of Fox Farms Happy Frog/Ocean Forest. For years I have grown in 10 gallon fabric pots with Ocean Forest on the bottom half/Happy Frog on the top. I do this because I find OF to be a bit hot and HF to be kinder to seedlings. I once ran an experiment where I grew out a group of white label, white widow strain autos with nothing but this soil and water. It can do the job.

Current grow - 10 gallon fabric pots, mixed varietal of autoflowers, all seeds purchased from Mephisto, six in total, half appear to be finishing slightly faster than the other half, but the earliest that harvesting should occur is ~2 weeks out.

What I have done so far:

Fed the plant according to schedule - currently feeding 2-8-4 at the standard 2 tsp per gallon/twice weekly feedings
Watered until run-off and measured the ph - used two ph meters (Vivosun/Bluelab) and received readings of 6.4-6.5. Soil run-off should optimally remain between 6.3-6.8 so soil ph doesn't appear to be the issue.
Measured par of lighting - using a FC8000 currently at 100% (800w) but have it anywhere between 2 and 6 inches further away than recommended at full power.
Lighting shedule is 24/0
Airflow appears to be more than adequate - currently using a Mars 6-inch fan with Mars filter. Fairly straight exhaust and good air flow at terminus
Temperature/Humidity - Averages are 78 deg/50% humidity
Looked for any pests, evidence of infection, mildew or mold. All negative.

I have ruled out anything I can think of as to why I am having this problem. I am pretty sure the plants will finish up before this could kill it, but it is driving me absolutely nuts.

Help??

 

[Lil Dab]

Looks like too much Nitrogen to me plus she looks like she is nearing her end

 

[WeedsInMyMind]

Looks like too much Nitrogen to me plus she looks like she is nearing her end

I realized I left out an important piece of information. This has been going on for the last three weeks. One week ago I trimmed out all of the dead or dying leaves. What you see now is new evidence of phosphate uptake problems from leaves that a week ago were fine. Three of the six are finishing and should come to harvest in 2-3 weeks. The smaller three are going to take a little longer. I'm absolutely positive the plants will all go the distance before this problem kills them, but no knowing the "why" is just bugging the shit out of me.

Thanks for responding! Much appreciated!

 

[Lil Dab]

but no knowing the "why" is just bugging the shit out of me.

I am the same way just want to know to hopefully prevent the next time thanks for the reps.. I am not the best at diagnosing myself

 

[Mañ'O'Green]

@WeedsInMyMind Welcome to AFN. The problem can be genetic coloring but I think you have had an environmental problem contributing to the leaf coloring. My first thought is it looks like the pots may have become too dry at some point causing hydrophobic pockets in the soil. This will limit uptake of nutrients. FFOF and FFHF have plenty of calcium in the form of Dolomite Lime so it is unlikely you needed to add any. The other thing that comes to mind is the RH may have got too high or too low for the temperature in the tent/space. The leaves close the stomata preventing transpiration, without transpiration nutrients cannot move into the plant and Last but not least is running 24/0. Plants exude substances into the root biome at night that stimulate the microbes to produce more of whatever nutrient the plant needs. If this is not happening because there is no night time the microbe do not change what they are producing.

It is not a serious problem. I live where it is hard to control heat and RH and I often get that problem. It is going on in my grow right now. It does not cause much of a loss in yield or quality.

Chasing the problem by throwing nutrients at it may do more harm than good.

 

[WeedsInMyMind]

@WeedsInMyMind Welcome to AFN. The problem can be genetic coloring but I think you have had an environmental problem contributing to the leaf coloring. My first thought is it looks like the pots may have become too dry at some point causing hydrophobic pockets in the soil. This will limit uptake of nutrients. FFOF and FFHF have plenty of calcium in the form of Dolomite Lime so it is unlikely you needed to add any. The other thing that comes to mind is the RH may have got too high or too low for the temperature in the tent/space. The leaves close the stomata preventing transpiration, without transpiration nutrients cannot move into the plant and Last but not least is running 24/0. Plants exude substances into the root biome at night that stimulate the microbes to produce more of whatever nutrient the plant needs. If this is not happening because there is no night time the microbe do not change what they are producing.

It is not a serious problem. I live where it is hard to control heat and RH and I often get that problem. It is going on in my grow right now. It does not cause much of a loss in yield or quality.

Chasing the problem by throwing nutrients at it may do more harm than good.

Thank you for the thoughtful response! Much appreciated!

I'd happily hang my hat on genetics, but during this grow I decided to grow out a hodgepodge of strains. The only repeat in the grow is Stilton Special (X2), the other four are each different, so a total of five strains.

The dry pot idea may be the answer. I did go on vacation for a few weeks. I had my buddy set up for just plain water during that period, and he may have let it get too dry.

RH and temp are not an issue. I keep the tent monitored with Govee and the temp has fluctuated from 75 to 79 during the grow and the RH from 48 to 54.

I am brand new to autos. This is only my 5th grow with autoflowers having been a photo grower for many years. Is it your opinion that even autos should have a dark period? Because these have not.

Again, thanks for the helpful response.

 

[Mañ'O'Green]

Well that makes sense. The pots got dry, it looks like a nutrient problem, you flush several times and there a no microbes left to make the phosphorous available to the plant. All of the available nutrients have been washed out leaving behind the Dolomite Lime that does not wash out so your pot is way out of balance. I recommend to never flush soil. You can flush peat a little bit and coco/rock wool a lot.

If you have Recharge handy now is the time to use it with a good surfactant to make sure you don't have any dry pockets in the pots. Stop feeding calcium.

Yes Science shows that plants need a dark cycle. My own personal grows have demonstrated that they need a dark time. Even in the farthest north or south regions where landrace ruderalis cannabis grows have a dark period in the beginning and late growth of the plant. It may have very long days in the middle of it's growth. Change your light schedule to 18/6.

 

[WeedsInMyMind]

Thanks. These are so close to the finish line that I don't want to change up their environment on them at this point. The next batch is in the germination stage and I will set the lighting timer to your recommendation.

 

[Driver77]

Have you checked DLI?...I'm guessing with the fc8000 at 100% your way over what it should be. Too much DLI won't necessarily cause light burn but can cause the plant to burn itself out.