Leaves curling/burning sporadically. Whats the deal?

First off, hello!

I'm new to posting online about weed in any way, shape or form... I've done browsing on my own to learn what I can, but at some point that just doesn't cut it anymore... so here I am. I'm a beginner grower to be sure, so don't expect my knowledge to impress anyone, else I wouldn't be here seeking help in the first place.

On to my problem...

The basics: Indoor grow, tray of 30-32 girls, rockwool cubes, 2 lights, I water as needed (usually every 2-3 days when I feel it is starting to get a little light, and I water until it starts to come out of the bottom of the cube). Usually around week 6,7 of flower I start to notice 1-2 girls having issues with the leaves yellowing a bit and burning (almost like nute burn, but I don't THINK that's it)... but it will only be a girl here or there, not groups of them together. I'll upload pictures of the issues I'm having as well.

I've looked around the internet for pictures and descriptions of problems that best match what I'm seeing, but nothing seems to really stand out... light burn is the conclusion I come to... but sometimes the plants directly under the light have no issue and a plant on the corner of the tray starts to have a problem... so that doesn't make sense to me...

I'm hoping that someone has an answer so that I can keep my ladies healthy... I hate watching them burn...

Also, when I first notice the problem, I'll flush with straight RO water for a couple days (started this for nute burn just in case)... but that doesn't seem to really stop the problem... they burn up to the bud and then it starts to yellow... and it hurts my heart to watch it

It's so hard to tell in HPS lighting, but looks to me like they are overwatered, excess nitrogen and cal mag deficient.

I apologize for the pictures, cell phone camera and (as you said) HPS lighting... it makes for some terrible shots.

Thank you for the quick response... so it might be multiple issues rolled into one? It makes sense that this could happen, but I never really thought about it like that... duh me I suppose.

You definitely have a trace element lock out. Pic #7 looks just like boron deficiency. That or your PH is off. Again hard to say with the lighting.

Upon looking into your initial thoughts and checking the plants again with them in mind, I now see that the plant is only really having the burning/discoloration on the top portion... the bottom leaves are droopy, but not burnt or discolored.

From what I've read elsewhere, if the deficiency is with a mobile nutrient, problems will occur on older/lower leaves. If the nutrient is immobile, problems will occur on newer growth and the top portion of the plant... is this correct?

I calibrate my pH meter every few days and try to always feed at 5.8... though sometimes it will be 5.9 or 6.0 if the plant is a bit older, is this an issue? Should a hardline 5.8 be maintained at all times when feeding?

I've 86d the N nutrients (the mainly N nutrients) starting week 2 and on in flower now. I've also upped the CalMag from the lowest recommended dose to the highest recommended dose... I'll keep an eye out on the next sets to go through the weeks around where I normally have seen the issues and will have to see what happens.

bp07 said:

From what I've read elsewhere, if the deficiency is with a mobile nutrient, problems will occur on older/lower leaves. If the nutrient is immobile, problems will occur on newer growth and the top portion of the plant... is this correct?

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Yes, its correct. Your PH doesn't seem to be an issue. You want to keep it around 5.8 for hydro and 6.5 for soil.

If you can get a pic or 2 of the whole plant in normal lighting it would help. You can take a few pics with the flash on just after or before your lights come on or off. It won't mess with them at all.

If it's boron, new growth will emerge with burnt tips/margins.

Hotboxbudz said:

Yes, its correct. Your PH doesn't seem to be an issue. You want to keep it around 5.8 for hydro and 6.5 for soil.

If you can get a pic or 2 of the whole plant in normal lighting it would help. You can take a few pics with the flash on just after or before your lights come on or off. It won't mess with them at all.

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I will work on getting a picture today of this... around week 7 I start to remove the highest layer of fan leaves from the girls, so the pictures I get of this may not be the most helpful to look at...

Sometimes I will notice issues directly underneath the lights with plants having this same burning issue (I'm fairly certain its not a heat issue)... Could that possibly be because those plants receive the most light and burn their nutrients at a faster rate? Like... maybe they run out of a certain nutrient faster because they metabolize the food quicker, and therefore need higher doses or need to be replenished more often? I don't know, I'm just spitballing here and I'm a little baked too, so....

Merlot said:

If it's boron, new growth will emerge with burnt tips/margins.

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I use a height management nutrient during week 2 or 3 (depending on when I think they reach a good height), so I don't know if I'll be able to compare the "new growth" after this time, but this is good information for keeping an eye out for this before those weeks or during veg. Sometimes in veg I'll notice a couple of the really small girls' new leaves are toasted, I wonder if this might be whats causing that?

My biggest plant was throwing out the burnt new growth, so I did some research and all signs pointed to boron def as a result of under watering. I added an extra liter to that plants watering and the next node was back to normal.

Merlot said:

My biggest plant was throwing out the burnt new growth, so I did some research and all signs pointed to boron def as a result of under watering. I added an extra liter to that plants watering and the next node was back to normal.

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Interesting. With my "bad" girls, they all start green and healthy, and around week 6-7 (flower) start to yellow and burn on the top portions of the plants, usually the ones that are directly under the lights, though its sporadic and sometimes occurs on the outsides of the trays as well... Could it still be the same Boron issue if the leaves start healthy and stay that way for the first 6 weeks?

---Also, including some more pictures of what I believe to be the same problem, plus some pictures of the bottom leaves that remain green on plants that burn on top.

I truly appreciate your guys' input.

Looks like a PH issue to me. Boron def shows only on new growth.

Merlot said:

Looks like a PH issue to me. Boron def shows only on new growth.

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I've started to calibrate the pH meter daily now, and always feed 5.8-6.0... Would a pH issue account for the sporadic burning, as I always feed all the girls the same food and in the same manner... why does it only happen to a girl here or there instead of the whole tray?

As previously stated, I've upped the CalMag and cut out N nutrients from flower, so far I haven't seen any issues with my next set coming up, they're mid-6 right now, I'll watch them the next week or so and see...

Ideal soil PH is 6.5. If the new growth is good, then you should be ok.

whats your EC/ppm set to? How far away from the plants is your light? What micronutrients, if any, have you used or considered? Have you tried using a mycorrhizae supplement to allow better nutrient uptake? It seems that the final phases of flowering can be the hardest on the plant, especially when it has been storing up nutrients in the leaves and they are gone when it calls upon them. If you consistently remove the fan leaves during flower, it would be best to prepare the plant in the same fashion during veg so that it would be used to losing leaves. I personally favor the cutting in half technique to ensure that i allow more light to penetrate the canopy while leaving the much needed reserves where they are. Too much light could be causing a ramped consumption rate in the hotspots of the canopy. Against what most people say, I find raising my lights up to give more of an even light as opposed to intense one is best for me and my garden. Best of luck

IMHO, it seems to me that you are pushing your plants faster than they are ready to go. Too much light and not enough roots to uptake the nutrients needed. Back your light off 8"-12" and see how the plants respond. You may want to focus on improving root health and mass, in which case, I would recommend some Mycorrhizae inoculate like Great White or OregonismXXL. The plant will stretch to get more light only if necessary, not automatically. There are five key factors in the plants growth, a chain so to say, light-water-food-oxygen to roots-CO2. It's only as strong as it's weakest link. If everything is ready to go but the food isn't there, brown spots on your leaves appear. Our job as growers is to make sure that the plants can eat as much as possible. Not, get as big as possible, or green as possible, but eat as much as they can. We want the biggest flowers(in relation to the methods) with the best unfertilized seed sets as the end result. That's what they do. They eat in order to be able to create a seed set to proliferate. All of those five factors are key to eating, and the plant is feeding on itself because the food is not there for it, or it is unable to eat that food due to lockout or whatever reason.

bp07 said:

I've started to calibrate the pH meter daily now, and always feed 5.8-6.0... Would a pH issue account for the sporadic burning, as I always feed all the girls the same food and in the same manner... why does it only happen to a girl here or there instead of the whole tray?

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Chaos theory? LOL its not exactly the same. The plants i"m sure have different root masses, and those little bits could be the difference on its ability to uptake. Also, maybe try aerating your nutes for 24hrs before applying if not already with an airstone.
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Excerpt from the thread "Plant Moisture Stress" found on this site

2. High Heat - the plant is losing water via it’s leaves faster than what can be replaced by the root system. The leaf responds by leaf margin cupping or rolling (up or down) in order to conserve moisture. A good example is reflected by the appearance of broad-bladed turf grass on a hot summer day, high noon, with low soil moisture levels - the leaf blade will roll in and the grass will take on a dull, greyish-green appearance. Upon sunrise when moisture levels have returned to normal, the leaf blade will be flat. Lower the heat and concentrate on developing a large, robust root system by practicing sound plant culture. An efficient and effective root system will go a long way to prevent heat induced leaf dessication and leaf margin curling by supplying sufficient moisture for good plant health. One short episode of high heat is enough to permanently destroy leaf tissue and cause a general decline in the leaves affected, which often occurs to leaves found at the top of the plant located near HID lamps. The damaged leaf (usually) does not recover, no matter what you do. Bummer in the summer. One can only look to new growth for indications that the problem has been corrected.

3. High Light - yes, it’s true, you can give our faves too much light. Cannabis does not receive full sun from sunrise to sunset in its natural state. It is shaded or given reduced light levels because of adjacent plant material, cloudy conditions, rain, debris and dust collection on the leaf surface, twilight periods of early morning and late afternoon, and light intensity changes caused by a change in the seasons. Too much light mainly serves to bleach out and destroy chlorophyll as opposed to causing leaf cupping, but it often goes hand-in-hand with high heat for indoor growers. Again, back off on the light and concentrate on developing/maintaining an efficient and robust root system. Keep in mind that all but equatorial material receive less light during flowering than during the vegetative stage.

Hope this helps

Merlot said:

Looks like a PH issue to me. Boron def shows only on new growth.

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Looking at the new pic with the flash on, I agree. It looks like damage from PH fluctuations. Also I agree with Happyman. I think your lights might be to close or to strong for some of your girls. Wish I could help more. I have grown indoors, but its been a few years. I primary grow outdoors, and it comes with its own set of problems. Just hate seeing such beautiful plants having problems. I hope we can nail down what's wrong.

HappyMan420 said:

whats your EC/ppm set to? How far away from the plants is your light? What micronutrients, if any, have you used or considered? Have you tried using a mycorrhizae supplement to allow better nutrient uptake? It seems that the final phases of flowering can be the hardest on the plant, especially when it has been storing up nutrients in the leaves and they are gone when it calls upon them. If you consistently remove the fan leaves during flower, it would be best to prepare the plant in the same fashion during veg so that it would be used to losing leaves. I personally favor the cutting in half technique to ensure that i allow more light to penetrate the canopy while leaving the much needed reserves where they are. Too much light could be causing a ramped consumption rate in the hotspots of the canopy. Against what most people say, I find raising my lights up to give more of an even light as opposed to intense one is best for me and my garden. Best of luck

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Happyman420, Thank you for your post and for the information, the bolded line is something I've been wondering about lately... The ppm's change during flower, starting at about 1100 -wk 1, going to about 1500 -wk 3-4, then it'll drop to approx. 1300-1400 - wk 7. The lights are approx 2 ft above the canopy. I use a wide array of nutrients in my food mix... I'm not sure if these would be categorized as micronutrients or not... I have not tried a mycorrhizae supplement, you'd recommend this? Only for flower, or only for veg? Or should it be used the entire lifespan for best results? I remove the top layer of fan leaves at week 7, though often the burning issue will already be present when I am doing this. And if I see it early and raise the lights (as I'd thought it was heat stress previously) it will still continue to burn up the leaves until it reaches the nug. It's a terrible trainwreck to watch happen in slow-mo.

I'm still learning just how important the roots are... it makes sense they would be though. One of the things I've started doing the past month or so is to brew a "tea" (with guano and the such) and, once a week, try to flush out any salts that might build up in the cubes. I also use 3 ml/gal sm90 in my food when I feed (except in the tea). I always use pumps that pull air into the water, but I don't always let them sit overnight before feeding... should I start doing this?

Hotboxbudz said:

Looking at the new pic with the flash on, I agree. It looks like damage from PH fluctuations. Also I agree with Happyman. I think your lights might be to close or to strong for some of your girls. Wish I could help more. I have grown indoors, but its been a few years. I primary grow outdoors, and it comes with its own set of problems. Just hate seeing such beautiful plants having problems. I hope we can nail down what's wrong.

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I appreciate your kind words... these plants don't deserve to suffer like this. I hope so as well.

And thank you for your input and info as well, it takes a village! As I said before, I upped the CalMag and have only seen the issue on 1 plant in my next set of wk 7s (which is a huge change from 5-6 plants), and even that plant isn't getting it TOO bad. The rest all look healthy, so I feel you at least partially solved my problem from the get-go! Thank you! But there's always room for improvement for me, lots left to learn.