Bright yellow leaves during flowering

Hi, I’ve read a few posts about yellowing leaves and it seems there is a lot of different opinions mainly being that it is caused by a nutrient deficiency. I have an outdoor grow, about 3 weeks into flowering, top crop complete soil, mesh pots. My main concern is the sun. It is HOT. I mean hot as hell, upwards of 90F plus, everyday, no rain, and plants are in direct sunlight. That’s South America for ya… I check my PH religiously before watering due to early problems of browning leaf tips (lost a lot of early leaves). I noticed on one plant, the one that lost the least amount of leaves, the now larger leaves kind of make a canopy for the buds growing beneath them, shielding them from the sunlight somewhat. On one plant those larger canopy leaves don’t exist because they burned off about a month ago. Each pot is I0"x10" square mesh. Each plant takes about 1.5-2.0 liters every other day and the water is gone within 48 hours. Could this yellowing issue be due to under watering or over watering? I always water at night and am wondering should I water less each night or do a big watering every two days? Any info appreciated! Also, how do I add a specific nutrient?

I am not the guru here but pics would be a great benefit. I also just experienced yellowing of lower to mid leaves and am 4 weeks into flower. I Came to the conclusion it was a nitrogen deficiency. I removed damaged leaves, added nutes and they are looking much better. It’s my fault since I stopped giving nutes other than bloom after switching to flower. This is a first grow for me so also a learning experience and trial by fire. Post a few pics, others will be able to assist in your specific issue. Good luck!


i think the sun may be to blame. 90 and up is not ideal.

as for underwatering…i dont believe that would cause yellowing, at least not immediately. first signs of underwatering would be wilting/drooping. if left uncorrected i imagine would eventually lead to yellowing, based on lack of nutes going to plant.

you said you water at night. according to GrowBible. watering should be done at first light. there is isnt going to be any “drinking” during dark hours. so no need to have wetness there to potentially mildew or something.

post some pics if you can, will help a lot im sure.

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im no expert on this. hopefully @donaldj or @MacGyverStoner can respond with more accuracy.

if you know you are lacking a specific nutrient. you could make a solution with water and nutrient and use as a foliar feed. or, same concept but, add to the water you use for watering.

If these plants are in 5 gal pots adding a couple of litres every other day is too little they are probably drinking that every day I would water every day or water till overflow and wait till they are light and water again

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Well, I did take a pic to put up, but it was to dark I’ll try again tomorrow. Also, will start watering in the morning instead of at night as well as water everyday. The sun is so intense here you could probably put a swimming pool worth of water in the planter and it would dry up. Since they are in mesh pots I can feel the bottom of it to see if it’s damp or wet so I know that the base has gotten water. Do I want to keep that damp all the time? Or do I want to let it dry out a bit as not to over water?

Let it get almost dry to the touch about an inch and half down in the top layer and the bottom should be just about dry than water or feed when needed .

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water with a 10% run off expectation I water every 3 days and go through 15 gal on 7 plants in my flower room I judge almost exclusively by weight of pots

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Ok, so here are two pics of my plants that are in some trouble. The first pic shows the bright yellow leaves I mentioned earlier in the post. On that plant I counted about 12 leaves in all that are either bright yellow or on their way to being bright yellow. On my other two plants I noticed yellowing around the edge of the leaf with the middle still a nice green color. Second problem… I made a HUGE mistake last night and added a dash of plant food thinking it would help along the two plants that have fallen behind in flowering production. I woke up today to find severall leaves absolutely black and several more with dark brown tips. I did a small flush to test PH and the PH going in is exactly what’s coming out, it’s about 6.4 on average. I completely soaked the plants as they were dry as a bone almost all the way to the bottom. I do have a question. When watering the plants, since I have mesh pots, I water until the bottom is damp, but not dripping. Should I be putting in enough water to create a drip on the bottom, or just until it’s damp? I can only guess the black leaves are due to nutrient burn as they were not there before I added the plant food. The yellowing I am still stumped on. Thanks for any input!

Bring your ph to about 6.2 might be a better range if it’s swinging before you water or feed .

You should water the plants until water is slightly flowing out of the bottom. That is also the water you should ph test to get a root zone ph level. It takes me about 4litres of water to get run off in my pots, probably about 6 gal of soil in the pots. Very similar temps and constant sun where I’m growing but i only have to water every 3 days. try water till you get run off, feel the weight of the pot straight after, then let dry out for 2-3 days, feel the weight of the dry pot and water again. that way after a few times you will know when to water by weight of the pots. If you drench the soil till you get a good amount of runoff, you shouldn’t have to water every day.

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Actually the black leaves are likely due to a deficiency since if you are only watering to damp and not a run off every time your plants likely are getting a salt build up which is blocking nutrient uptake do a true flush using 3-4 times pots volume of water. Rinse your soil out with straight ph’d water I would bet that your ppm is crazy high on your run off now soil is saturated :wink:
this is your most likely culprit How to Stop Phosphorus Deficiencies In Marijuana Plants - ILGM

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When I read that the pH coming out was EXACTLY the same as the pH going in that strongly suggested lock up (hint)

Donald awesome catch! -thank you for all the help

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Did you find the solution to the problem? After seeing the pics of the rusty spots im thinking you have a phosphorus deficiency going on. Hope you solved your problem though

Lol i saw the march date and thought this was a newer one. Hahahahahah