Nute burn or heat stress?


I am in the 5th week of flowering and the leaves are yellow and curling up and dried out. Is it nute burn or heat stress?


Looks more like a nute burn. It looks like possibly a nutrient toxicity or nutrient lockout. What is the pH of the water you give it, the pH of any nutrient mixes/plant food you give it, and most importantly, the pH in the root zone?

If it is nute burn, a EC/TDS reading of the run-off could help, you can also measure this for pH to get an idea of what the pH might be in the soil or root zone.

Happy growing,



I ph my water at 6.0 to 6.5. The thing is I’ve grown 3 batches before and never had an issue. All of a sudden I get this. I did 2 things differently this time. I added another HPS light and cut back on nutes to about half as much as usual.


Ok, and the pH at the root zone?



I checked the run off and it is 5.5. Would low humidity cause this?


5.5 is way to low for soil you in to raise to 6.5


If 6.5 is going in the top, but 5.5 comes out the bottom, that is not good.

If the pH going in the top is 6.5, you want about the same coming out the bottom, 6.5. It can be a little lower, but certainly no lower than 6.0, and this is why, this is a rough idea, but this is kind of how you need to think about it…

6.5 goes in, but 5.5 comes out, this means 1.0 is being cancelled out in the soil, and this kind of means your root zone could be as much as that 1.0 lower than what came out, as low as maybe 4.5. Things might not be as out of whack as the math might suggest, but you get the idea.

You can flush the soil with 7.5 pH water, or maybe even higher, until your runoff comes out to about 6.5. You’ll probably want to flush with about at least 3 times the amount of water than the volume of soil.

The reason your pH is so far off, is possibly that the lowered nutrients did not provide enough of what your plant normally can use, and the plant in flower will then add to the acidity because of ion exchange at the roots.

Something else that can sometimes cause problems is a nutrient or mineral salt build up in the soil, and that can cause a nutrient lockout as well. This can also throw off the pH, but I don’t think this is your situation, as that usually results in an overly alkali pH

Either way, the flush will restore a balance to the pH as well as flushing any excessive nutrient or mineral salts that might be building up in the soil. After you have reached the proper pH, you can water with properly pH’ed full strength nutrient mix as you would normally during a feeding at this time.

happy growing,



By the way, if you put the back of your hand at the level of the leaves, and if it isn’t too hot for your hand, then it most likely isn’t too hot for your leaves.



nute burn for sure have you flushed your roots even one time during grow cycle I just addressed this issue today 9 weeks into grow and plants were starting to show signs of potassium lock out. Try flushing your plants with straight properly ph’d water. When I say flush I mean rinsing, over water plant in sink or bath tub basicaly triple or 4 times as much water as you would normally give let the water rinse through media. Stop to test run off periodically measure for ppm 200-300. once you have reached somewhere in that range let plants drain out a bit then feed as per normal. Test the run off from your feeding it should be right ppm for your stage of growth. I recommend RO or distilled water to rinse it will carry away most of the salts built up if you caught it early enough plants will recover in several days but keep in mind nute burnt leaves won’t recover this will simply allow new growth and undamaged growth to remain undamaged.

Hope this helps


at a ph of 5.5 in soil you are looking at potassium lock out


Yup, and the buds actually need more potassium during flowering.

@ashflash52, Fix the pH and it should be fine.


Sorry MacGyver answered the question after you already had didn’t read whole thread didn’t mean to step on toes. Seen picture and since was doing homework to solve/prevent same problem yesterday blurted out same answer. Though I did know about ion exchange awesome info



No problem, lol.



secondary reason I chose to flush is that I am flipping several plants to flower they are going to get a dose of bud blood 0-39-25 .5g a liter which will push my ppm up by 200-250 once of prevention…


I would really like to know the cause of this problem…like I said before, I’ve never had this happen in 4 or 5 batches and then all of a sudden. I was thinking because I added an extra light it affected the temperature in the closet and my plants dried out quicker. I know sometimes it was up to 30 degrees.


Actually, I already told you. The more intense light might have been a contributor because of increased metabolic activity in the plant – but it was most likely because you reduced the concentration of your nutrients, and that caused enough of of an imbalance that the ion and cation exchange, that normally happens during flower, at the roots, this can cause an acidity in the root zone, the soil, if it doesn’t have enough pH stabilizing minerals available to it. Reducing the nutrients, there are minerals in those nutrients, you reduce the amount of those minerals available. The fact that you reduced your nutrient concentration contributed to this normal drive towards the more acidic during flowering, if not being the sole reason for your problems this time around.

The drop in pH and increased acidity is a common occurrence during flowering with cannabis, it is normal, but many nutrients for flowering help balance out this by providing a better balance of nutrients to keep the ion and cation exchange more balanced as well as calcium and magnesium compounds that can help buffer pH, dolomite lime is a perfect example of this.