Leaf darkening mystery

[plan500]

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

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 2 to 3 days apart and see the difference.

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

 

[Creeperpark]

Nitrogen and magnesium will turn the leaf darker green.

 

[WingzHauser]

The dark color is the result of slowed starch metabolism due to low phosphorus. Clawing is low B. N makes the green stuff, P and B work together to move the green stuff out of the leaves.

No such thing as nitrogen toxicity, other than ammonium stress in the roots or something. How can excess photosynthesis be problematic? Only when that photosynthate is not metabolizing/moving out of the leaves and stems. I don't know why the go to answer for pot growers is to reduce N or dim lights to fix slow translocation/metabolism. Everyone thinks they are overfeeding this plant Nitrogen, I haven't seen the limit yet. I don't know why N takes the blame for everything in Cannabis, the biggest hit to indoor quality is the lack of atmospheric nitrogen being drug into the soil by the weather. 2nd is the lack of seasonal P uptake signaling.

 

[Ca++]

Second to last pic really shows it. It's that kind of bluey green. Looks alright in isolation, but with others to compare to, it's just off green.

It does seem a little late. Perhaps they were working with stored P for a while.

 

[Creeperpark]

If you are keeping your EC steady and using your fertilizer appropriately there shouldn't be a problem. It's important to follow the manufacturer's nutrient sequence by the book. Using fertilizers the way they were designed will always give the best results. Don't change the tables the only thing that's changeable is the ppm used per watering per week.

 

[NEED 4 SEED]

You are the first grower I know of who complains about healthier plants. Everyone else is trying to get dark green leaves instead of yellow ones. I don't see a problem there.

 

[Creeperpark]

I have seen in the past where people want to modify the nutrient sequence by changing the ratio. Thinking that if I give my plant a little more bloom it will give me more bulk. Don't do that because the manufacturer's nutrient sequence is complete. If you change the nutrient model you will get side effects that are not always good.

The only exception to the rule is the Lucas Formula when using the General hydroponics Flora series. The two parts mix has a 5-5-5 equal ratio without using Grow Nutrient.
However, the Lucas formula is mainly designed for DWC and other hydroponics systems, and not for soil-less mixes.

Keep the manufactures ratio for the best results.

 

[TanzanianMagic]

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

View attachment 18874394


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 2 to 3 days apart and see the difference.

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

View attachment 18874402

View attachment 18874403

They need more magnesium. The dark leaves, combined with the fact that they're in early flowering means magnesium.

0.1 EC (50 PPM) of Epsom Salt (MgSO4) should take care of it.

 

[stiff]

If you use tap water maybe check the water analysis report of your council..maybe you find any hints in there. Good luck

 

[plan500]

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.

* 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?

Here is also my environment parameters.

Any suggestions are welcomed, including off-topic recommendations.

 

[plan500]

The dark color is the result of slowed starch metabolism due to low phosphorus. Clawing is low B. N makes the green stuff, P and B work together to move the green stuff out of the leaves.

No such thing as nitrogen toxicity, other than ammonium stress in the roots or something. How can excess photosynthesis be problematic? Only when that photosynthate is not metabolizing/moving out of the leaves and stems. I don't know why the go to answer for pot growers is to reduce N or dim lights to fix slow translocation/metabolism. Everyone thinks they are overfeeding this plant Nitrogen, I haven't seen the limit yet. I don't know why N takes the blame for everything in Cannabis, the biggest hit to indoor quality is the lack of atmospheric nitrogen being drug into the soil by the weather. 2nd is the lack of seasonal P uptake signaling.

This is the recommended shedule from the manufacturer, which I find rediculous. Perhaps it is for general use, not cannabis specifically. Anyway, I have intoduced additional Phosphorous in week 3 rather than week 4. Just 0.3 but still.

 

[plan500]

I have seen in the past where people want to modify the nutrient sequence by changing the ratio. Thinking that if I give my plant a little more bloom it will give me more bulk. Don't do that because the manufacturer's nutrient sequence is complete. If you change the nutrient model you will get side effects that are not always good.

The only exception to the rule is the Lucas Formula when using the General hydroponics Flora series. The two parts mix has a 5-5-5 equal ratio without using Grow Nutrient.
However, the Lucas formula is mainly designed for DWC and other hydroponics systems, and not for soil-less mixes.

Keep the manufactures ratio for the best results.

If I follow the manufacturer's shedule this will get very ugly. It has taken me 20+ grows to adjust this shedule so that I get some decent results.

 

[plan500]

They need more magnesium. The dark leaves, combined with the fact that they're in early flowering means magnesium.

0.1 EC (50 PPM) of Epsom Salt (MgSO4) should take care of it.

This sounds too easy to be the solutiuon. Also there isn't any magnesium def simptoms. I've been researching a lot about this darkening and never sow anything related to magnesium.

 

[Creeperpark]

If I follow the manufacturer's shedule this will get very ugly. It has taken me 20+ grows to adjust this shedule so that I get some decent results.

You miss understood, you use the manufactures ratio but not the same quantity. I use only 1/3 or less on a regular basis.

 

[plan500]

I understand now.

In terms of PPMs I think I have the balance based on 4 weeks vegging, no training and my specific environment conditions.

In terms of the ratios, you are correct that I have based them on my logic and interpretation. I used to have a schedule that was initially based on just the basic Alga Bloom and Green sensation in the ratios 4to1, 3/1 as shown in manufacturer feed chart. Unfortunately back then I had other factors troubling my grow, so I haven't been able to see the potential of this chart. Later I changed to custom feeding schedule thinking that the recommended ratios are more for general plants and not specifically cannabis. I added more P/K .. a lot more.

Would you recommend to get rid of the additional P/K and use the base food and Green sensation in the exact ratios from the chart 3/1, 3.5/1, 4/1 ?

 

[Creeperpark]

I understand now.

In terms of PPMs I think I have the balance based on 4 weeks vegging, no training and my specific environment conditions.

In terms of the ratios, you are correct that I have based them on my logic and interpretation. I used to have a schedule that was initially based on just the basic Alga Bloom and Green sensation in the ratios 4to1, 3/1 as shown in manufacturer feed chart. Unfortunately back then I had other factors troubling my grow, so I haven't been able to see the potential of this chart. Later I changed to custom feeding schedule thinking that the recommended ratios are more for general plants and not specifically cannabis. I added more P/K .. a lot more.

Would you recommend to get rid of the additional P/K and use the base food and Green sensation in the exact ratios from the chart 3/1, 3.5/1, 4/1 ?

What matters most is the nutrient sequence. NOT nutrient quantity.

 

[Creeperpark]

LIEBIG’S LAW OF THE MINIMUM​

Plants will naturally follow this sequence, so it’s in our best interest to familiarize ourselves with it. It’s important to understand that a plant can only perform as well as their most deficient nutrient allows them to. Without the earlier functions, the later functions won’t work optimally.

Biochemical Sequencing 101 - Aptus Holland

Traditional agriculture operates by looking at plant like they are machines. We tend to think a little different at Aptus. We believe we should look at plants as living creatures, just like you and me.

aptus-holland.com

 

[plan500]

I've seen this sequence before, It make sense that is something is missing it will bottleneck the rest. I will spend some more time researching the brand of nutes I use and possibly follow manufacturers recommendations more closely. Thank you for giving me that direction.

 

[TanzanianMagic]

This sounds too easy to be the solutiuon. Also there isn't any magnesium def simptoms. I've been researching a lot about this darkening and never sow anything related to magnesium.

Well I've been growing for 20 years now, and darkening of the leaves is characteristic for Mg deficiency.