Too much light? Upward-curving leaves and foxtailing

medidedicated said:
One thing that makes me think it may not be the light is I think you said youve been dimming them but the lower leafs taco too which unusual. Also that your temps are perfectly fine.
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I said it might be the light because i think the plant, when saturated with light, curls its new leaves upward to reduce light absorption. The upper leaves are a bit crispy too.

However, I forgot to mention something important. It hasn't even been two weeks since I moved the grow to a much cooler location and under the air conditioning. At one point, it reached 31°C.
 
Thats ok temps still I was rockin 91F this past summer. The switch might of called for dialing in the new location. I get slightly different grown in my new veg tent. Let alone if I flowered down there.
 
Petinha88 said:
I said it might be the light because i think the plant, when saturated with light, curls its new leaves upward to reduce light absorption. The upper leaves are a bit crispy too.

However, I forgot to mention something important. It hasn't even been two weeks since I moved the grow to a much cooler location and under the air conditioning. At one point, it reached 31°C.
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Cannabis will grow well at 31°. The optimal temperature for vegetative growth is 30°C/85°F.

The plants are reacting to too much light.

A mature cannabis plant will thrive in 800-1000µmol, the difference being some strains are able to use more light than others.

If a grow is not able to tolerate that much light, it's probably because there's something wrong in the grow environment. I've seen two grows, on another cannabis site, where the plants weren't able to tolerate > 500µmol and, in both cases, poor watering practices had turned the soil hygrophobic.
 
Hello, sorry for the delay, but I was running several tests to try to understand what happened.

I started growing other plants in my apartment, and among them was a tomato plant. It was outdoors, in a cool and ventilated spot, with a different soil medium, and the tomato leaves started looking just like cannabis leaves. The only explanation was the water.
WhatsApp Image 2025-03-10 at 13.42.17.jpegrdwf ef.jpeg

I found out that the water was from a well and had a high mineral content (I believe it was calcium and magnesium), with an EC of 0.24 mS/cm, while mineral water has an EC of 0.01 mS/cm.
dfgdf.jpeg
When I measured the runoff, the EC was above 5.0 mS/cm because I was following Biobizz fertilizer instructions. I tried to do a flush, but it was already too late.

To be sure, I started a plant under the same conditions as before, but only used mineral water and Biobizz fertilizers, and the plant grew beautiful and healthy. Unfortunately, it didn’t produce resin (unknown seed).
dfgfd.jpegffgfeg.jpeg

Now, I’ve started three new seeds using organic soil, mycorrhizae, and only mineral water, but the symptoms seem to be returning.
hgfds.jpeghgfd.jpegjhgfds.jpeg

This time, I believe it might be light stress due to the IR and UV spectrum. My two 120W quantum boards have LM301H chips + IR and UV, and I always left them on. But I read that you shouldn’t do that. This would explain the abnormal plant growth and stretching between nodes. I turned off the IR and UV yesterday (after two weeks of being on), and I hope this is the last issue (lol).
iuytr.jpeg
Do you think the plant actually gets stressed with these IR and UV LEDs always on along with the normal light?

Oh, the plants turned out ugly, had foxtailing, but besides not producing seeds, they had good taste and effects (Bubba Kush and Grape Kush).
IMG_0775.jpg

Regarding light intensity, using Photone correctly, I verified that everything was within the expected range, even leaving room to increase the intensity.
 
Delps8 said:
The plants are reacting to too much light.

A mature cannabis plant will thrive in 800-1000µmol, the difference being some strains are able to use more light than others.

If a grow is not able to tolerate that much light, it's probably because there's something wrong in the grow environment. I've seen two grows, on another cannabis site, where the plants weren't able to tolerate > 500µmol and, in both cases, poor watering practices had turned the soil hygrophobic.
Click to expand...
As an outdoor grower I'm so curious about all of this. The sun can put out about 2000 µmol/m2/sec, so why is over 1000µmol hard on an indoor plant? Outdoor plants can definitely suffer from to much heat or not enough humidity but I've never heard of an outdoor plant suffering from to much light.
Why the difference in ability to uptake light in indoor vs outdoor environments?
 
Funkentelechy said:
As an outdoor grower I'm so curious about all of this. The sun can put out about 2000 µmol/m2/sec, so why is over 1000µmol hard on an indoor plant? Outdoor plants can definitely suffer from to much heat or not enough humidity but I've never heard of an outdoor plant suffering from to much light.
Why the difference in ability to uptake light in indoor vs outdoor environments?
Click to expand...
The sun doesn't put out that intensity for the duration above the horizons. It's variable.

It would be nice to have a light that could match the exact intensity of the sun, as it progresses through the day.
 
Funkentelechy said:
As an outdoor grower I'm so curious about all of this. The sun can put out about 2000 µmol/m2/sec, so why is over 1000µmol hard on an indoor plant? Outdoor plants can definitely suffer from to much heat or not enough humidity but I've never heard of an outdoor plant suffering from to much light.
Why the difference in ability to uptake light in indoor vs outdoor environments?
Click to expand...
Outdoor plants are conditioned for the enviroment with genetic stratagies to deal with high light levels. They can also be hardened off when moving from inside to outside.

I never worried about DLI on a tomato but mellons need high dli and will fail with just a week or 2 of crappy weather.
When I started growing cannabis inside I got a light sensor and was amazed at the light levels on a sunny hot day. I was like every inch of plant will be at saturation point for hours

nope. look up your local dli. the usda and a few universities have it online. My best light monthes are june july and august at about 51 dli. very within the range of cannabis.
 
Petinha88 said:
Hi all,

I’ve grown three cycles without any issues in a 40x40 cm grow with a 120W quantum board using Samsung L301H LEDs.

I decided to upgrade to an 80x80 cm grow and added a second 120W quantum board. After that, I ran into problems. In the last cycle, I had upward-curving leaves, foxtailing and lots of seeds.

In this new cycle, when I switched to flowering, the same issues started again.

There are no pests; I did a thorough inspection with a 60x magnifying glass. The temperature inside the grow is between 24°C and 27°C at the plant base with the AC off, and I have a fan blowing at the top and an exhaust fan. I’m watering with pH 6.2 to 6.3, doing organic growing, and there’s no over-fertilization.

I fixed all the issues from the previous cycle, but the problems persist.

The only variable that stayed the same is the amount of light. I started with 20% power on each quantum board, and just before switching the photoperiod, each was at 50% power. So, 4 days ago I removed one quantum board and set the remaining one to 60%, since I read that too much light can cause these problems, even if it’s not too hot.

I don’t have a ppfd meter, only the cell that’s not accurate.

If that’s not the issue, I don’t know what to think anymore.

Do you guys think it’s possible that they’re like this because of too much light only?


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Get one of these photone is rubbish! very inacurate ive been using this uni-t lux meter for years and its a much better way of measuring light distance and intensity. You use a conversion equation to convert lux into ppfd i consider it just as important as a decent ph meter.
 

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cat shit said:
Get one of these photone is rubbish! very inacurate ive been using this uni-t lux meter for years and its a much better way of measuring light distance and intensity. You use a conversion equation to convert lux into ppfd i consider it just as important as a decent ph meter.
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This is my recent grow using the uni-t lux meter from sprout to finish
 

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cat shit said:
Get one of these photone is rubbish! very inacurate ive been using this uni-t lux meter for years and its a much better way of measuring light distance and intensity. You use a conversion equation to convert lux into ppfd i consider it just as important as a decent ph meter.
Click to expand...
Get the Bluetooth version, and you can use it with the android app "PPFD Meter"
 
Petinha88 said:
Hello, sorry for the delay, but I was running several tests to try to understand what happened.

I started growing other plants in my apartment, and among them was a tomato plant. It was outdoors, in a cool and ventilated spot, with a different soil medium, and the tomato leaves started looking just like cannabis leaves. The only explanation was the water.
View attachment 5456009View attachment 5456010

I found out that the water was from a well and had a high mineral content (I believe it was calcium and magnesium), with an EC of 0.24 mS/cm, while mineral water has an EC of 0.01 mS/cm.
View attachment 5456011
When I measured the runoff, the EC was above 5.0 mS/cm because I was following Biobizz fertilizer instructions. I tried to do a flush, but it was already too late.

To be sure, I started a plant under the same conditions as before, but only used mineral water and Biobizz fertilizers, and the plant grew beautiful and healthy. Unfortunately, it didn’t produce resin (unknown seed).
View attachment 5456012View attachment 5456013

Now, I’ve started three new seeds using organic soil, mycorrhizae, and only mineral water, but the symptoms seem to be returning.
View attachment 5456015View attachment 5456014View attachment 5456016

This time, I believe it might be light stress due to the IR and UV spectrum. My two 120W quantum boards have LM301H chips + IR and UV, and I always left them on. But I read that you shouldn’t do that. This would explain the abnormal plant growth and stretching between nodes. I turned off the IR and UV yesterday (after two weeks of being on), and I hope this is the last issue (lol).
View attachment 5456017
Do you think the plant actually gets stressed with these IR and UV LEDs always on along with the normal light?

Oh, the plants turned out ugly, had foxtailing, but besides not producing seeds, they had good taste and effects (Bubba Kush and Grape Kush).
View attachment 5456018

Regarding light intensity, using Photone correctly, I verified that everything was within the expected range, even leaving room to increase the intensity.
Click to expand...
Read thru to see if you figured out what happened cause initial photos didnt look like too much light to me; sure some tacoing but missing all tell tale signs of led over lighting: bleached green and purple stems would normally show before tacoing. Glad you got it figured out:)
 
Petinha88 said:
Hello, sorry for the delay, but I was running several tests to try to understand what happened.

I started growing other plants in my apartment, and among them was a tomato plant. It was outdoors, in a cool and ventilated spot, with a different soil medium, and the tomato leaves started looking just like cannabis leaves. The only explanation was the water.
View attachment 5456009View attachment 5456010

I found out that the water was from a well and had a high mineral content (I believe it was calcium and magnesium), with an EC of 0.24 mS/cm, while mineral water has an EC of 0.01 mS/cm.
View attachment 5456011
When I measured the runoff, the EC was above 5.0 mS/cm because I was following Biobizz fertilizer instructions. I tried to do a flush, but it was already too late.

To be sure, I started a plant under the same conditions as before, but only used mineral water and Biobizz fertilizers, and the plant grew beautiful and healthy. Unfortunately, it didn’t produce resin (unknown seed).
View attachment 5456012View attachment 5456013

Now, I’ve started three new seeds using organic soil, mycorrhizae, and only mineral water, but the symptoms seem to be returning.
View attachment 5456015View attachment 5456014View attachment 5456016

This time, I believe it might be light stress due to the IR and UV spectrum. My two 120W quantum boards have LM301H chips + IR and UV, and I always left them on. But I read that you shouldn’t do that. This would explain the abnormal plant growth and stretching between nodes. I turned off the IR and UV yesterday (after two weeks of being on), and I hope this is the last issue (lol).
View attachment 5456017
Do you think the plant actually gets stressed with these IR and UV LEDs always on along with the normal light?

Oh, the plants turned out ugly, had foxtailing, but besides not producing seeds, they had good taste and effects (Bubba Kush and Grape Kush).
View attachment 5456018

Regarding light intensity, using Photone correctly, I verified that everything was within the expected range, even leaving room to increase the intensity.
Click to expand...
I don't believe those uv and ir diodes are all that powerful. It also doesn't look like light stress to me. There would be other symptoms.

If it's not heat, insects, or input water, I dunno what else it could be. They look healthy otherwise.

Is it only on new growth? I get twisted, wonky looking leaves on new growth occasionally
 
Funkentelechy said:
As an outdoor grower I'm so curious about all of this. The sun can put out about 2000 µmol/m2/sec, so why is over 1000µmol hard on an indoor plant? Outdoor plants can definitely suffer from to much heat or not enough humidity but I've never heard of an outdoor plant suffering from to much light.
Why the difference in ability to uptake light in indoor vs outdoor environments?
Click to expand...
Good question. I do not know the answer.
 
Hollatchaboy said:
The sun doesn't put out that intensity for the duration above the horizons. It's variable.
Click to expand...
Very true but I don't see that it explains the behavior.

A cannabis plant grown indoors will show symptoms of excesss light when exposed to 1400µmol (for argument's sake) for just a few minutes. I don't think cannabis plants growing outdoors exhibit the same behavior.

Hollatchaboy said:
It would be nice to have a light that could match the exact intensity of the sun, as it progresses through the day.
Click to expand...
Manufacturers are adding that to their lights. Spider has it in their grow app. Other companies will be forced to follow suit.
 
cat shit said:
Get one of these photone is rubbish! very inacurate ive been using this uni-t lux meter for years and its a much better way of measuring light distance and intensity. You use a conversion equation to convert lux into ppfd i consider it just as important as a decent ph meter.
Click to expand...
I wouldn't call Photone rubbish but I would recommend only as a last resort.

The conversion factor is very, very important. Uni-T says that their lux meter is accurate to 5%± but using the wrong conversion factor will swamp the 5% inaccuracy (which is the same level of accuracy to which an Apogee is calibrated).

I've attached a document I wrote to make it easier to do the conversion from lux to PPFD (hence the title).
 

Attachments

Delps8 said:
I wouldn't call Photone rubbish but I would recommend only as a last resort.

The conversion factor is very, very important. Uni-T says that their lux meter is accurate to 5%± but using the wrong conversion factor will swamp the 5% inaccuracy (which is the same level of accuracy to which an Apogee is calibrated).

I've attached a document I wrote to make it easier to do the conversion from lux to PPFD (hence the title).
Click to expand...
I have been hating on the currently available conversion tables. Will check out yours.
 
Its genetics. Ive seen some of my plants, that contain some ruderalis genes, really struggle with high ppfd. I actually found a thread where a seasoned grower demonstrated that an old school skunk under ppfd of 500 prevented rhodelization. That same skunk, under high ppfd caused the plant to throw bananas, and herm in some cases.

Im currently running 3 different strains, 2 of them threw sterile bananas, due to high ppfd. One those strains has taco leaves... lol!

One of the strains is undisturbed and stacking like crazy.

Genetics
 
Jimski said:
I have been hating on the currently available conversion tables. Will check out yours.
Click to expand...
I followed shane from migro he had a conversion table for the btu posted online. after i asked delphs on here, he gave me his insights and after using his equation i got better results ie the plants received more light, so i guess its only as good as the equation. Still good to have an idea of intensity
 
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