Leaves are cupping! Overwatering or pH?

GroLex · Jul 21, 2023

Back story:

These plants are 4 weeks from being cloned. Growing in 70/30 coco/perlite mix, with 2" of chunk perlite in the bottom and 2-3" of shredded Coco on top. They sit 36" below Metal Halide lamps set to 50%. Temperature is 26c max for lights on and 21-22c lights off. Humidity is between 55-75%. Watering a few litres a day with a mix of 375 PPM and ph 5.8-5.9.

A week after transplant from solo cups to 5 gallon fabric bags, a few plants started showing some cupping on the upper leaves and on new growth. New growth has slight twisting as well. I checked the runoff and got values of under 450 PPM with a pH of 5.6-5.7.

Worried the pH was dropping out of range, I started watering heavily over a few days (4L a day) with a higher pH (6.0-6.2) in hopes to get the pH of the substrate back to 5.8-6.0. PPM was under 400 for these events.

The runoff is now around 425 PPM and 5.9-6.0 pH BUT....now I have some drooping on the fan leaves along with the leaf cupping.

Looking up causes of leaves cupping I found the following:

- Bad pH
- Overwatering
- Calcium/Magnesium deficiency (lockout due to bad pH)
- Underwatering
- Heat/Light stress
- Bugs
- High humidity

I know there isn't any bugs.

I definitely haven't underwatered.

I THINK I can eliminate Heat (26c MAX).

Lamps are 36" above tops at 50% strength so I THINK I can eliminate that.

I use calmag with every watering (once a day) so unless the pH is locking it out, it shouldn't be that.

That leaves overwatering...

It has to be overwatering right?

Dub_City405 · Jul 21, 2023

Typically when they are looking like that it's heat/humidity/light burn stress. You can cut back just a tad bit on the water. But I believe when I overwater they will droop and taco downward.

deerman12 · Jul 21, 2023

In my opinion, If you are watering everyday, it is probably overwatering. I water about every 5 days when my pots feel light picking them up.

GroLex · Jul 21, 2023

Dub_City405 said:
Typically when they are looking like that it's heat/humidity/light burn stress. You can cut back just a tad bit on the water. But I believe when I overwater they will droop and taco downward.

Ok I'll jack the lamps up as high as they'll go for starters. Keeping the humidity down comes with higher heat for my situation...how much heat is too much? Could I go as high as 28c lights on and 23-24 lights off?

GroLex · Jul 21, 2023

deerman12 said:
In my opinion, If you are watering everyday, it is probably overwatering. I water about every 5 days when my pots feel light picking them up.

Thanks, I thought so too. I'll definitely stop watering for a few days to start with. I always read that coco needs to be wet all the time so it's super confusing.

Dub_City405 · Jul 21, 2023

It shouldn't be humidity because they are in a younger stage.

Try to water less and move those lights up a tad bit. Also. The temp say when the lights are out drops to 65 but when the lights are on it jumps to 85. That 20 degree difference will shock the plant as well. It seems shocked. Gotta try everything to fix it in this stage so when you get to flower it's a smooth 8 to 10 weeks pure diamonds.

GroLex · Jul 21, 2023

Dub_City405 said:
It shouldn't be humidity because they are in a younger stage.

Try to water less and move those lights up a tad bit. Also. The temp say when the lights are out drops to 65 but when the lights are on it jumps to 85. That 20 degree difference will shock the plant as well. It seems shocked. Gotta try everything to fix it in this stage so when you get to flower it's a smooth 8 to 10 weeks pure diamonds.

Will for sure water less and raise lamps. I know what you mean, looks shocked/stressed for sure. My temperature sticks to 69F (21c) lights off and 78F (26c) though so shouldn't be any shock there unless that's just too cold for lights off?

ArtfulCodger · Jul 21, 2023

Tough to tell from the pics, but is the curling more severe as you move up the plants? If so, that says light stress to me.

GroLex · Jul 21, 2023

ArtfulCodger said:
Tough to tell from the pics, but is the curling more severe as you move up the plants? If so, that says light stress to me.

I'd say it starts about halfway up. Lower leaves are fine but new growth is coming out cupped and twisted

Deadstill · Jul 21, 2023

36 inches below Metal Halides? How many watts are these Metal Halides?

GroLex · Jul 21, 2023

Deadstill said:
36 inches below Metal Halides? How many watts are these Metal Halides?

600w but running at 50%...was trying to eliminate light stress as a cause. Figured that's definitely a safe distance, maybe not?

Deadstill · Jul 21, 2023

Do you have access to one of those infrared thermometers by chance? Curious to know what the temperature on the surface of those leaves is.. But very well could be light related. It sounds like you've covered almost all the bases so unless you've got root zone issues...

It wouldn't hurt to raise the lights a good 8 to 12 inches and see what happens, maybe integrate an oscillating fan if you haven't one already? Blowing across the top sections of the plants, oscillating, might help as well.

Smokey0418 · Jul 21, 2023

And the reason for such a low ppm?
Just adding calmag to my water is 180 , by the time I add fertilizer to hydro is 800 and in dirt I use the directions so 1600.
Perhaps there hungry too.

GroLex · Jul 21, 2023

Deadstill said:
Do you have access to one of those infrared thermometers by chance? Curious to know what the temperature on the surface of those leaves is.. But very well could be light related. It sounds like you've covered almost all the bases so unless you've got root zone issues...

It wouldn't hurt to raise the lights a good 8 to 12 inches and see what happens, maybe integrate an oscillating fan if you haven't one already? Blowing across the top sections of the plants, oscillating, might help as well.

I don't have one of those but I'll be raising lamps as soon as they turn on today. I've got oscillating fans running in there, maybe I'll turn up the speed too. Thanks

GroLex · Jul 21, 2023

Smokey0418 said:
And the reason for such a low ppm?
Just adding calmag to my water is 180 , by the time I add fertilizer to hydro is 800 and in dirt I use the directions so 1600.
Perhaps there hungry too.

I had some leaf clawing and burnt leaf tips so I backed off the PPM. You're right though, it could be underfed at this point too.

Chronic Monster · Jul 21, 2023

Just a couple thoughts on the tacoing, sometimes too much air movement, too dry(humidity not moisture in your growing medium) or possibly broad mites or hemp russet mites. Them mites are so small you would need a scope to see them though.
Hope you get it figured out.

GroLex · Jul 21, 2023

Chronic Monster said:
Just a couple thoughts on the tacoing, sometimes too much air movement, too dry(humidity not moisture in your growing medium) or possibly broad mites or hemp russet mites. Them mites are so small you would need a scope to see them though.
Hope you get it figured out.

Appreciate the input. I could turn the fans down but it doesn't seem too strong of air movement. Low humidity isn't the issue either, as it's 55-75%. So maybe TOO humid if anything. I can say it isn't bugs. I've looked with a jeweler loupe. Bugs don't seem to like coco, haven't seen anything outside of the random fungus gnat in 10 grows.

Chronic Monster · Jul 21, 2023

Well, just my .02 Id turn your fans down then. I used a jewelers loop before, couldn't see until I pulled out the 100x.
That said Im pretty sure it's the fan.

trustyagut · Jul 22, 2023

Hi, not sure if you sorted the issue yet, just wanted to say my plants looked exactly like those leaves a couple weeks ago, turned out I needed to raise the oscillating fan for them to uncurl themselves and straighten back out

GroLex · Jul 22, 2023

trustyagut said:
Hi, not sure if you sorted the issue yet, just wanted to say my plants looked exactly like those leaves a couple weeks ago, turned out I needed to raise the oscillating fan for them to uncurl themselves and straighten back out

Thanks for the reply. Did you mean you raised the height of the fan or the speed?

Leaves are cupping! Overwatering or pH?

Leaves are cupping! Overwatering or pH?

GroLex

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Leaves are cupping! Overwatering or pH?

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