Lower leaves begin to turn yellow - Need some help

[dedistraki]

I am growing Jack Herer under 720 watt cfl bulbs in 20l pot in soil. It's one and a half month old and still in vegetative stage. At first lower leaves started to look unhealthy but now they are turning a little yellow. I am using fox farm trio. Grow big consentration 33% and Big bloom 100% because its organic and can not harm the plant. Started using nutes a month ago but havent flushed yet as i was not using much nutes. Also tips of new leaves are a little yellow but as leaves become bigger they dissapear. Light is 24/0 because as it is cold i can not control temperature when the light is off, so i am waiting for March to turn lights 12/12 from 24/0.

First 2 pics are new ones

 

[LED209]

Lower leaves turning yellow is often a sign of nitrogen deficiency. Nitrogen is a very Mobile nutrient that when a plant starts to get bigger wants to give most of it to the growing tips getting the most light. If your aren't giving enough the plant will cannibalize or sacrifice some of its older growth to keep up with the new. I would up the N until the first couple weeks into flower then back off it again and go with more of the PK. Keep an eye on it and make sure your ph is in check. Good luck dude!


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[LED209]

Also the new growth in my experience always starts out as a lighter shade of green and tends to darken as the leaves mature. That's why you notice it one day and not the next. Hope that helps too


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[KingstonRabbi]

Ditto on both the above. I would up the Grow Big to 1/2 dosage.

Also needs magnesium. Lots of purple in stems. That would also contribute to yellowing. Use either Cal/Mag or tablespoon of epsom salts.

 

[Integrum Stultus]

Purple stems aren't necessarily a precursor to a deficiency, they're also genetic. I have a Cherry Bomb auto with purple stems. No adverse affect to the plant or upcoming harvest Sunday.


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[KingstonRabbi]

True. I have a couple strains that do that too. I think Jack Herer is strain that doesn't usually, but I could be wrong.

 

[OldSchool 64]

After looking at ur pics..id check ur ph first before u start experimenting with any nutes..
99% of the time its an issue..do you check it EVERY time u water or assume its ok.
Also need to check soil run off..
If any of those are an issue..
Just flush her out with ph ed water good.3 times the pot size..then water last with ur nutes..
Bet she perks right up..

When in doubt flush her out..first before anything else.
good luck on ur grow
peace!!