Leaf darkening mystery

plan500

Well-Known Member
Someone should be able to recognize this, and it happens on a repetitive base, with different strains.

Screenshot 2023-07-04 001234.png

Right around week 4-5, there is a sudden darkening of the canopy that happens literally overnight. One day they are all light green and lime and the next they get dark and remain that way until then end. Results are fine, but I think this is not normal and there should be a way to keep them light green until the end.

Nitrogen is the main focus of my experiments, I have reduced it a lot, especially after I flip them, I have attempted to reduce it further even getting yellowing in lower leaves, however I can never seem to save them from darkening eventually. Sometimes beginning of week 6.

My main question is, could this effect be anything else than excess nitrogen? Does something else cause this darkening?
Also, is this perhaps normal? I know it is not strain related as I have tried various.

I do see some clawing and the smaller plants and those with weaker genetics definitely show nitrogen excess symptoms, at least that's my read.

This has been happening my 5-6 grows as this is a repetitive production cycle. All other factors the same, reducing Nitrogen has not shown great improvement. The following pair images are taken 1 to 2 days apart and see the difference.

Plants are visibly happy at all times, but something is off.

Screenshot 2023-07-04 001415.png
Screenshot 2023-07-05 233552.png
 

plan500

Well-Known Member
By week 5 of flower I am only giving them 0.3-0.4 ml/L CalMag. I doubt this can cause an issue.
 

plan500

Well-Known Member
Could it be caused by too high VPD too early in flower. I do control VPD and in week 4-5 it gets to 1.2-1.3. Could plants get too much nitrogen due to enhanced water absorbtion. I do grow at 30 degrees Celsius, around 65% humidity in week 5 specifically.
 
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plan500

Well-Known Member
Can someone confirm that plants can actually look light green by the end of flowering - weeks 8-9? With all my experience of more than 20 grows, I have never been able to keep them light green by the end. What are your observations?
 

Billy the Mountain

Well-Known Member
Nah it can
Opinions are irrelevant; provide your source

Science is real

Here is but one source you can peruse to learn more about Ca and nutrient utilization:

Both Ca deficiency and excessive Ca inhibit N absorption and utilization, and the adverse effects of Ca deficiency on seedling growth and N metabolism are greater than those associated with excessive Ca2+ supply (Xing et al., 2021)

Xing Y., Zhu Z. L., Wang F., Zhang X., Li B. Y., Liu Z. X., et al.. (2021). Role of calcium as a possible regulator of growth and nitrate nitrogen metabolism in apple dwarf rootstock seedlings. Scient Horticult. 276, 109740. 10.1016/j.scienta.2020.109740
 
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yosim

Well-Known Member
Opinions are irrelevant; provide your source

Science is real

Here is but one source you can peruse to learn more about Ca and nutrient utilization:

Both Ca deficiency and excessive Ca inhibit N absorption and utilization, and the adverse effects of Ca deficiency on seedling growth and N metabolism are greater than those associated with excessive Ca2+ supply (Xing et al., 2021)

Xing Y., Zhu Z. L., Wang F., Zhang X., Li B. Y., Liu Z. X., et al.. (2021). Role of calcium as a possible regulator of growth and nitrate nitrogen metabolism in apple dwarf rootstock seedlings. Scient Horticult. 276, 109740. 10.1016/j.scienta.2020.109740
seen it on my own plants but whatever
 

plan500

Well-Known Member
Thank you all for the answers, I will provide some more information that will hopefully help you identify the problem.

This is a SOG, no training grow, 4 weeks growing and 9 weeks flowering. I use organic base nutrients from Plagron.

Alga Grow NPK (4-2-4) in growing stage (3-4 weeks).
Plagron Alga Bloom NPK (3-2-5) + Green sensation NPK (0-9-10) + a little P/K booster (0-13-14) (mineral)

Also in flowering I brew compost teas with almost every watering. There is some extra nitrogen in the tea which amounts to additional 30-50ppm but I have tried to cut on the tea until week 5 and it didn't help with the darkening problem.

Calmag is from General Hydroponics, I believe it was 1 or 0 nitrogen in the NPK. Intentionally I found the one with least nitrogen.

I also added PK with the idea to further reduce the base nutrient that seems to have a lot of nitrogen.

Overall I feed a lot under what is suggested by Plagron calculator.

1691701564448.png

* some theories I work on include:

- high temps of 30-31 degrees (84-87F) might cause excessive evaporation and water uptake, that might forcibly make the plants to update excessive amounts of Nitrogen. I've read that this temperature range is fine and recommended for LED, and I keep VPD in range. What do you think?
Although temps in weeks 1-5 are more around 28-29 degrees. (82-84 F)

- I notice that my C02 tends to accumulate at night above 2000ppm. Could this be a problem?

- Low light intensity (Plants are unable to use all nitrogen)

Here is also my environment parameters.

1691702491153.png

Any suggestions are welcomed, including off-topic recommendations.
 
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plan500

Well-Known Member
Some more images from around week 5-6. Strain is Cookies Gelato from Royal Queen seeds. This particular grow turned out fine, but I've had much worst in the past.

20230701_160810.jpg20230701_160815.jpg20230701_185646.jpg
 

coreywebster

Well-Known Member
Some strains are dark , others not so much.
I've never aimed for lime green leaves .

You're correct that high temps will cause more uptake and plants tend to take more N when it's available.

But the original pictures show no signs of having too much N or been odd in colour, simply healthy plants.

Don't make the mistake of thinking you know more than a nutrient company at providing a balanced feed .

The reason they are lighter in early flower is because the energy is going into stretch and new bud sites and the nutrient uptake doesn't keep up with the rapid development.
Then that rapid growth steadies and the nutrient uptake catches up and your leaves darken.

You are imagining problems that don't exist as far as I can see
 

obijohn

Well-Known Member
Plants looks healthy, I wouldn't be concerned about the color darkening, IMO usually means they have enough nitrogen.
 
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