Signs and all possible causes
Big leaves clawing. Sometimes but not always they can get a dark green colour, sometimes shiny. Usually starts randomly or from the bottom. Think how much nitrogen you have been using, sometimes the recommended doses can be too much for phenotypes or strains that are not very hungry.
If it happens only on the top canopy and the leaves dont show particularly any of the previous symptoms:
1. Light or heat stress: either the intensity of the light or the heat is making the leaves unhappy.
2. Wind stress: you most likely have the fan that you use to move air pointing towards the plants. Dont do that, the fan must be ABOVE the canopy and never pointing directly towards the plants in a small indoors.
3. Overwatering or underwatering.
Treatments
1. Nitrogen toxicity
1.1. If you are using synthetic nutrients, a quick flush might help you. If you flush, youre removing all the nutrients not just nitrogen so reintroduce them in a more moderate dose shortly after or the plant might show deficiencies.
1.2. If youre using organic liquid nutrients and microorganisms: organic should give you enough time to catch the symptoms early but if its already too late you will wanna flush heavily and restore nutrients and microorganisms with a light feeding. Organic is harder to remove from the soil hence why the heavy flush. It will take some time for your soil to go back to what it was, a week or two maybe, stunted or slow growth might happen during that time.
1.3. If youre using organic dry ammendments mixed with the soil: a heavy flush might help you, or make it worse, youre kinda screwed, pray for it to not make your buds ugly and unsmokable. If youre top dressing though, remove the top layer of the soil and reintroduce more moderate quantities, you can always add more later if the plant asks you to.
2. Light or heat stress: either dimm the lights a little bit or pull them higher. Dont go closer than what your retailer recommends to make sure youre not overwhelming the plant with light. For heat, even if you have a thermometer in the tent the temperature close to the LEDs is gonna be much higher, place your hand where your top canopy is, if the temperature is noticeable hoter (by noticeable I mean that you can tell the difference, doesnt need to be a lot) then you might have a problem. If you wanna test the temperature; more than 80ºF or 30ºC can cause stress to the plant, less than 50ºF or 12ºC can cause stress to the plant (when its too cold sometimes the leaves might show blue colour, not to confuse with the natural blue that some strains have. In this case the blue is gonna come with the leaf looking "weird"). High temperature fluctuations between day and night cycle can also cause stress.
3. Wind stress: move your fan higher, if its still causing a lot of movement point it upwards. You want a gentle breeze so the leaves barely move and the thin stems stay mostly in place.
4. Overwatering or underwatering: if the soil is moist, let it dry, if the plant goes mostly to normal after a few days youre overwatering. If the soil is dry and the pot doesnt weight much, give it a good watering until you get some runoff, if it goes mostly back to normal then that was the problem. If youre using textile pots you will notice that when you underwater dry pockets form making the water come from the sides of the pot instead of going down. That can also happen if you water very fast, preventing the water to reach the bottom. When in doubt, you can do a light bottom watering after you water the plant from the top. Try to avoid the medium from going too dry so you dont have to keep bottom watering your plants or watering very slowly because of the dry pockets.
TO CONSIDER
Damaged leaves will never go back to normal, the only time you will see leaves recovering is when theyre thirsty and you water them or had too much water and you let them recover, and even then you can cause permanet damage if not adressed in time. Ex: you can cause root rot if you overwater a lot, in which case youre gonna cause irreversible damage to the plant, not only the leaves but leaves are the ones that speak (let you know something is wrong). You will know that the problem is over when it stops getting worse, if its not getting better after adressing all these points, your plant is most likely damaged beyond repair.
There are countless sites that will give you similar information, thats because they cant diagnose your plants because they dont know what youre feeding them, how often you water, what lights and what distance and a long etc... many times you will see people like me using such links because honestly, writing a post like this every time someone asks if they have nitrogen toxicity or whats happening to their plants is tiring. Hopefully this post will kill a few birds with one stone but new posts about it will keep appearing.
Fuck (excuse My English) ... Divide the dosage of nitrogen in two and you will have no problem.
