Potassium Deficiency? Or Heat stress?

Hello all,

First post here, it looks like I have a problem with one of my two plants in my rubbermaid grow.

My Rubbermaid Grow:
- 35 Gallon Rubbermaid
- Sidewalls covered in reflective xmas paper (Will soon be painting flat white)
- 2x 68w (300w Equ. to Incondescent) CFL's 2700k
- 1x 120mm Fan for outtake
- 2x 80mm Fans for intake
- PSU w/ fan powering fans
- Currently on 24/7 light cycle
- Temperature: Currently now around 80-83F, was around 85-90 previously with just 1 80mm as an outake and no intake fans. I also now rotate putting a frozen bottle of water next to my plants every 12-15 hours.

The plants had been repotted about a week and a half ago. They have good root structures. But within the last week (A couple of days ago I brought the temp down w/ the new fans. And today I started putting the frozen bottles in. One of my plants is really loving life, really taking off. This plant has no signs of anything wrong with it.) I have noticed a problem with my other plant.

The plant that I am worried about has leaves that feel dry. The very new shoots are starting to yellow on their tips. Also, many of the bottom older leaves are starting to crack (Due to dryness) and are showing browness (First light green) in the middle of the leaf. This is why I don't believe its heat stress (Or maybe its a combination of heat stress and Potassium Deficiency?) The shoots look healthy except for the very top shoots that now have a little bit of yellowing on the very end of the tips. It also seems like the plant with the problem has stunted its growth compared to the other one. I am imagining that heat stress will stunt growth, but so will a potassium deficiency no? I don't have any sort of water in my grow box to increase the humidty. Is this a problem?

I checked PH of the water, and its running just a little lower than 7.0, probably around 6.8. (I haven't got a digital meter yet, but I used some test strips I had sitting around) I had been using tap water (Soft water from well), but I am now using hard water from our well. I have not touched any nutrients the entire grow period, (Now around 5-6 weeks). Today I mixed a gallon of water to a quarter tsp of Miracle Grow (25-8-16). (Half strength solution off of box)

This is a soil mix, (Schultz) with the stats:
Total Nitrogen: .12%
Total Phosphate: .09%
Total Potash: .07%

It also says: Part of the fertilizer materials have been polymer coated to provide the following slow-release nutrients: .09% N, .02% P2O5, .04% K20

I will be LST'ing with these plants, because of the height limitation.

I feel that it isn't heat stress because my other plant is really flourishing. Is there anything that anybody can recommend? And what do you guys think?

its not heat stress , i know what it is but im having a mental blank. might be boron deff tho

http://www.ganjaguerrilla.net/ <<<< check it out.

Credit the following to Uncle Ben. Thread here: https://www.rollitup.org/marijuana-plant-problems/150004-plant-moisture-stress-symptoms-solutions.html

1. Over-fertilizing - the most common cause of leaf cupping aka leaf margin rolling, leaf margin burn, and leaf tip curl/burn is the overzealous use of too much plant food in relationship to factors such as plant size, vigor and rate of growth. The first unit of a plant to show moisture stress is the leaf at its margins and/or tips, reflected by margin rolling (cupping) or burning. Sometimes copper colored necrotic spots show in the leaf also. A hard, crispy feel to the leaf frequently occurs as well, as opposed to a soft and cool feel of a happy leaf. When you have a high concentration of salts in solution (or in the root medium) compared to lower salinity levels found in the plant’s tissue, water is actually drawn out of the plant across the root gradient in order to fix the ppm imbalance. IOW, this is a natural, osmotic response that serves to equalize salinity levels on both sides of the root’s epidermal gradient. Back off on the amount and/or frequency of plant food. Too much plant food can also burn the roots, especially the sensitive root tips and hairs, which then creates another set of problems such as nutrient deficiencies. A note for the bio folks - as soil dries, the concentration of the remaining salts rises further exacerbating the problem.

Sound familiar? The soil they were in was probably fine but let get a little too dry so it caused some burn. Adding more salts (ferts) will make it worse. Flush excess salts and let it go for a few days.

doogleef said:

Credit the following to Uncle Ben. Thread here: https://www.rollitup.org/marijuana-plant-problems/150004-plant-moisture-stress-symptoms-solutions.html

1. Over-fertilizing - the most common cause of leaf cupping aka leaf margin rolling, leaf margin burn, and leaf tip curl/burn is the overzealous use of too much plant food in relationship to factors such as plant size, vigor and rate of growth. The first unit of a plant to show moisture stress is the leaf at its margins and/or tips, reflected by margin rolling (cupping) or burning. Sometimes copper colored necrotic spots show in the leaf also. A hard, crispy feel to the leaf frequently occurs as well, as opposed to a soft and cool feel of a happy leaf. When you have a high concentration of salts in solution (or in the root medium) compared to lower salinity levels found in the plant’s tissue, water is actually drawn out of the plant across the root gradient in order to fix the ppm imbalance. IOW, this is a natural, osmotic response that serves to equalize salinity levels on both sides of the root’s epidermal gradient. Back off on the amount and/or frequency of plant food. Too much plant food can also burn the roots, especially the sensitive root tips and hairs, which then creates another set of problems such as nutrient deficiencies. A note for the bio folks - as soil dries, the concentration of the remaining salts rises further exacerbating the problem.

Sound familiar? The soil they were in was probably fine but let get a little too dry so it caused some burn. Adding more salts (ferts) will make it worse. Flush excess salts and let it go for a few days.

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OK, so your saying its a nute burn? Mind you, I haven't added any nutrients prior to this. Are you talking about the nutrients in the soil, or could it possibly be the soft water that was previously added? (Salt is added to remove hardness of water) Or did I let the soil get too dry? Also, your bolded response says theres too much moisture? Is that too much humidity? Thanks everyone for the responses so far.

how often do you water?

acidbox420 said:

how often do you water?

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Typically I will water once the top of the soil doesn't have much moisture left in it. However, the plant with the problems has the top of the soil wet now for the past 2-3 days. Last night (Due to the thoughts of the nutrient deficiency) I added a small amount of water (Enough to layer the top of the soil (2-3mm deep) w/ half strength MG for a few seconds till it sinked in. I haven't been watering the plant until water comes out of the bottom.

Do you think that I should completely flush until the water comes out of the soil clear?

ok well if you'r gonna do that do it now or let that soil dry out cause i think you'r root's want oxygen.Did you add that MG mix you made if so you should flush and if you flush you should add some Hydrogen peroxide (H2O2) to the last gallon you flush with. you add 1/3 of a cup of 3% solution(what you can get at the grocery store) to a gallon of water also when you flush use 3 times the amount of water to your pot size so if you have a 1 gallon pot you put 3 gallons through and dont flood you'r pot let the water slowly seep through

acidbox420 said:

ok well if you'r gonna do that do it now or let that soil dry out cause i think you'r root's want oxygen.Did you add that MG mix you made if so you should flush and if you flush you should add some Hydrogen peroxide (H2O2) to the last gallon you flush with. you add 1/3 of a cup of 3% solution(what you can get at the grocery store) to a gallon of water also when you flush use 3 times the amount of water to your pot size so if you have a 1 gallon pot you put 3 gallons through and dont flood you'r pot let the water slowly seep through

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OK, I'm going to flush and see what happens. Will I ever see a recovery of those leaves or will they continue to die? Also, should I cut the leaves that are dying at all? I haven't seen much information on trimming dying leaves. (Maybe because you shouldn't do it?!?) Thanks acidbox, i'll try this.

EDIT: Another question, should I use hard or soft water? Any ideas on this? Also can't find info on this.

That def looks like nute burn to me - not just the spots, but starting down on the low leaves like that is pretty typical. That's not very serious - your plant should pull out of it with proper watering.

Here's what you have: you have 1) small plants 2) pre-ferted soil and 3) not a whole lotta light strength. These three things added together = no demand for added nutrients right now.

Don't add any more nutrients. I wouldn't "flush" as in adding tons of water until it flows clear either. I would let them go until they need water again. At that point, water thoroughly enough that water flows out the bottom of the pots. Not tons and tons... just enough to prove that you've thoroughly wetted your medium.

The fact that one plant is doing great and the other is troubled doesn't mean anything. I've got the same thing right now - plants thriving, plants struggling side-by-side in absolutely the same set of conditions. Each plant is an individual, as inconvenient as that is.

RollinGreen said:

OK, I'm going to flush and see what happens. Will I ever see a recovery of those leaves or will they continue to die? Also, should I cut the leaves that are dying at all? I haven't seen much information on trimming dying leaves. (Maybe because you shouldn't do it?!?) Thanks acidbox, i'll try this.

EDIT: Another question, should I use hard or soft water? Any ideas on this? Also can't find info on this.

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I wouldn't do it (flush). The damaged leaves never recover, but the healthy tissue still works for the plant. I'd leave it be.

i buy like 10 1 gallon bottles of distilled water for like 30 cents a gallon and my ladys love me for it it seemed like no matter what i did wen useing tap eventually something went wrong also people say with soil you should flush like every month and a half i end up flushing at the first signs of nute problems unless it's just yellowing and leaves will fall off when there ready at most just lightly mess with the stem if it's dead doing that will make it fall off if not leave em be

OK, so I'm going to not touch the dead leaves at all. I just did a quarter-flush(?), I continually put a half cup of water (and a bit of hydrogen peroxide mixed w/ the water) in the pot until it would drain out, and then I'd do it again. I put maybe a total of about half the water as there is soil in the pot. I also did a quick ph test of the runoff water and it seems very acidic! (Somewhere in the range of 5.5-and 6.0 I believe) I know my tap water is around 6.8 as I tested this as well. Should I just leave the plant now and just water as normal? I also am running into conflicting information as far as general watering goes. I see some people water once or twice a week, but completely drench the plant until there is run off. Others just water a until the soil is wet. What do you guys think?

RollinGreen said:

OK, so I'm going to not touch the dead leaves at all. I just did a quarter-flush(?), I continually put a half cup of water (and a bit of hydrogen peroxide mixed w/ the water) in the pot until it would drain out, and then I'd do it again. I put maybe a total of about half the water as there is soil in the pot. I also did a quick ph test of the runoff water and it seems very acidic! (Somewhere in the range of 5.5-and 6.0 I believe) I know my tap water is around 6.8 as I tested this as well. Should I just leave the plant now and just water as normal? I also am running into conflicting information as far as general watering goes. I see some people water once or twice a week, but completely drench the plant until there is run off. Others just water a until the soil is wet. What do you guys think?

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If it were me, I would now just back off and let things settle for about a week. At that point, they should be about ready for another watering. At which point I would water fully until I got a little runoff. From there, I'd try to get into a routine -- water thoroughly, let dry, water thoroughly. That should hold you out for the next 2-4 weeks.

Your runoff pH is a little low, but not by much. I wouldn't mess around with any pH manipulation. By getting into a good watering cycle, you'll be flushing away organic waste from root respiration, which is probably accumulating from too tentative of a watering cycle.

When you go into flower and your plants shoot up, their water demand will increase and you have to follow along with that. My last years' plants went from needing water once a week to needing it every other day. Then it trails off again at the very end...

stop adding salt to your water either im prettys sure your plants dont like it , if your water is hard go pickup some water softner stuff from your local aquarium

Soft water = less PPM is better. The salts in the soil (without adding mg) got too hot. Likely because it was let get to dry which makes the available salts at the root more concentrated (less water = more salts by %, get it?) I saw you decided to flush. Good call. 1/2 - 1 gallon water per gallon o dirt should be enough. Dont want to totally leach it.

The "top of the soil" trick is bunk. Best way by far is the lift test. Water before the pot gets too light. Many newbs are very afraid over overwatering, with good reason, but the real issue comes when you water to the point where there is no air left in the soil. If you have proper drainage it is pretty tough to overwater.

I was having the same problem , i just went to week 7 of the fox farm nutz guide and all 3 of my plants started showing bad signs of that nuit burn. so i just got done doing a system flush and im gonna hope my plants can recover. also i was dealing with a damm spider mite issue and used some ORGANACIDE which smells like fish pussy hahahah no joke and i though that this leaf issue might be from that, anyway im gonna hope they recover because this is my first time growing and im looking forward to tasing my finished product.