Potassium deficiency? Or heat stress? Or soil pH too high?

[Emeraldo]

A month ago, we had high temps (104F/40C) and, at the same time, high winds that whipped the 5 foot tall plants, snapping them this way then that. At the time I noticed injury to the leaves, the serrations turning upward in a kind of little cup. At first, I though all these symptoms were just windburn damage and nothing further.

Since then, the injuries to many leaves have continued to turn brown and yellow, and have some or all of the following:

• leaf tips turning a rust brown (not unlike a nute burn)
• serrations along the edge of leaves turning the same rust brown color
• a yellow stripe along the edge of the rust brown streak
• curling and crumbling of leaves
• often even smaller new leaf growth turns almost completely brown and crumbles

Here some photos of my Super Lemon Haze, which is the most affected.

IMG_1920.jpeg

• Emeraldo
• Jul 15, 2020

IMG_1919.jpeg

• Emeraldo
• Jul 15, 2020

IMG_1914.jpeg

• Emeraldo
• Jul 15, 2020

IMG_1911.jpeg

• Emeraldo
• Jul 15, 2020

IMG_1892.jpeg

• Emeraldo
• Jul 11, 2020

IMG_1871.jpeg

• Emeraldo
• Jul 11, 2020

edge with minor damage, sunny (Blackberry)

IMG_1883.jpeg

• Emeraldo
• Jul 11, 2020

Blackberry fan leaf with windburn damage and consequent yellowing

My photos above match pretty well growweedeasy's photos on potassium deficiency.

How to fix Cannabis Potassium Deficiency (K) Pics & Symptoms

Leaves with a potassium deficiency have yellow, brown, or burnt edges and tips. It may look like nutrient burn, but the leaf margins also turn yellow.

www.growweedeasy.com

But from what I've read, this can happen even with sufficient K in the soil. Apparently the wind and heat stress could be the cause. It is a potassium deficiency, but it's not for lack of potassium. The heat stress may have triggered a lockdown in the plant, which is unable to absorb the potassium that is there.

Alternatively, it could also be that my soil pH is too high; according to growwedeasy, potassium is best absorbed at the lower end of the ideal 6.0-7.0 pH range. To top it off, Greenhouse Seeds, in their video on how to grow Super Lemon Haze, suggests a soil pH of 5.5, which is probably way lower than my soil pH.

Does anyone have experience resolving this kind of issue? My tap water is pH 7.1 and hasn't been a problem so far, but if SLH has a special need for 5.5, I can pH the water down to 5.5, no problem. What would you experienced growers do? Has anyone seen this before? Thanks for a response!

Emeraldo

 

[adudecalledjay]

A month ago, we had high temps (104F/40C) and, at the same time, high winds that whipped the 5 foot tall plants, snapping them this way then that. At the time I noticed injury to the leaves, the serrations turning upward in a kind of little cup. At first, I though all these symptoms were just windburn damage and nothing further.

Since then, the injuries to many leaves have continued to turn brown and yellow, and have some or all of the following:

• leaf tips turning a rust brown (not unlike a nute burn)
• serrations along the edge of leaves turning the same rust brown color
• a yellow stripe along the edge of the rust brown streak
• curling and crumbling of leaves
• often even smaller new leaf growth turns almost completely brown and crumbles

Here some photos of my Super Lemon Haze, which is the most affected.

IMG_1920.jpeg

• Emeraldo
• Jul 15, 2020

IMG_1919.jpeg

• Emeraldo
• Jul 15, 2020

IMG_1914.jpeg

• Emeraldo
• Jul 15, 2020

IMG_1911.jpeg

• Emeraldo
• Jul 15, 2020

IMG_1892.jpeg

• Emeraldo
• Jul 11, 2020

IMG_1871.jpeg

• Emeraldo
• Jul 11, 2020

edge with minor damage, sunny (Blackberry)

IMG_1883.jpeg

• Emeraldo
• Jul 11, 2020

Blackberry fan leaf with windburn damage and consequent yellowing

My photos above match pretty well growweedeasy's photos on potassium deficiency.

How to fix Cannabis Potassium Deficiency (K) Pics & Symptoms

Leaves with a potassium deficiency have yellow, brown, or burnt edges and tips. It may look like nutrient burn, but the leaf margins also turn yellow.

www.growweedeasy.com

But from what I've read, this can happen even with sufficient K in the soil. Apparently the wind and heat stress could be the cause. It is a potassium deficiency, but it's not for lack of potassium. The heat stress may have triggered a lockdown in the plant, which is unable to absorb the potassium that is there.

Alternatively, it could also be that my soil pH is too high; according to growwedeasy, potassium is best absorbed at the lower end of the ideal 6.0-7.0 pH range. To top it off, Greenhouse Seeds, in their video on how to grow Super Lemon Haze, suggests a soil pH of 5.5, which is probably way lower than my soil pH.

Does anyone have experience resolving this kind of issue? My tap water is pH 7.1 and hasn't been a problem so far, but if SLH has a special need for 5.5, I can pH the water down to 5.5, no problem. What would you experienced growers do? Has anyone seen this before? Thanks for a response!

Emeraldo

Another possibility could be excess potassium too!

 

[Emeraldo]

Another possibility could be excess potassium too!

Thanks. Would a K-toxicity or excess look the same?

 

[Emeraldo]

Looking at the leaf tips again this morning, I see that newer and newest leaf growth higher on the plants and at the top, there is no browning or yellowing or curling. Only on the lower half of the Super Lemon Haze, for example; the top leaves are unaffected. The affected leaves were in fact new growth at the time of the heat wave.

That suggests that this "deficiency" was in fact heat stress. My feeling tells me there is no K-"deficiency" in the soil, and I amended the soil earlier this year with kelp meal, alfalfa meal, and langbeinite, all containing K. But something had caused a lockout -- heat, or maybe soil pH.

The other three affected plants in the grow are not as affected as the SLH, for example Acapulco Gold also has some brown leaf tips, but not higher up. The affected growth was new growth about a month ago. New growth since that time is not affected.

However, out of caution, since the breeder GHS recommends a soil pH of 5.5, I will try to adjust soil pH downward to 5.5 or so. Will also pH the water for all other plants to pH 6.0, just to make sure K can be absorbed.

 

[adudecalledjay]

Thanks. Would a K-toxicity or excess look the same?

Yeah, I thought I'd mention it because they look surprisingly similar and you seemed fairly confident it wasn't a lack of potassium

 

[adudecalledjay]

Looking at the leaf tips again this morning, I see that newer and newest leaf growth higher on the plants and at the top, there is no browning or yellowing or curling. Only on the lower half of the Super Lemon Haze, for example; the top leaves are unaffected. The affected leaves were in fact new growth at the time of the heat wave.

That suggests that this "deficiency" was in fact heat stress. My feeling tells me there is no K-"deficiency" in the soil, and I amened the soil earlier this year with kelp meal, alfalfa meal, and langbeinite, all containing K. But something had caused a lockout -- heat, or maybe soil pH.

The other three affected plants in the grow are not as affected as the SLH, for example Acapulco Gold also has some brown leaf tips, but not higher up. The affected growth was new growth about a month ago. New growth since that time is not affected.

However, out of caution, since the breeder GHS recommends a soil pH of 5.5, I will try to adjust soil pH downward to 5.5 or so. Will also pH the water for all other plants to pH 6.0, just to make sure K can be absorbed.

Could very well be pH. If I add just the tiniest bit of kelp meal to my compost tea my pH doubles from 7 to 8 -- presumably from the salt content of the kelp meal. I have had heat stress before and haven't had this particular issue, but it would make intuitive sense that the plant would draw up more water and thus any issues with the soil would be amplified. But I've always been a hydro guy and have very little experience with soil -- excess heat may be a completely different beast in soil!

 

[Emeraldo]

Thanks for that Jay. I didn't realize kelp meal has the effect of raising pH. I'll have to take that into account going forward.

I used kelp meal this year for the first time. Seemed like a good idea, rich in K. I got two 2 lb bags of Dr. Earth Kelp Meal for amending about 90 gallons of soil. In mixing it up, I noticed the amount of kelp meal in each bag was kind of skimpy and the first bag was used up so quickly I dumped in the second one as well. No wonder it comes in small 2 lb bags!

Could that amount of kelp meal raise the soil pH to the point that the Super Lemon Haze, which (according to Greenhouse Seeds) likes soil pH at 5.5, could experience a lockout? Possibly. Add the extreme heat in June, when it was up to 104F. The extreme heat causes the plant to use a lot of water, amplifying soil issues because potassium is a key element regulating the plant's ability to absorb and use water. So there are two good reasons for this leaf damage. I'll need to test the soil pH but lost my soil pH meter. Getting a new soil pH meter to do that. In the meantime, I'm flushing the SLH's soil with water @ 5.5.

Thanks again! It is starting to make sense now.

 

[FelipeBlu]

Hiya Emeraldo!

I have had the same issue - it was a combination of sunburn/heat stress, letting the plant dry out too much, and then fertigating with too strong a solution for rehydration. It did recover somewhat, but it was an Auto and it hurried its finish.

I don’t understand the recommendation to grow SLH in pH 5.5 soil - goes counter to everything you read/experience. IMO, I wouldn’t worry about trying to change the soil pH. Just get her back on a normal feeding and maybe provide some shade at midday.

 

[Emeraldo]

Hiya Emeraldo!

I have had the same issue - it was a combination of sunburn/heat stress, letting the plant dry out too much, and then fertigating with too strong a solution for rehydration. It did recover somewhat, but it was an Auto and it hurried its finish.

I don’t understand the recommendation to grow SLH in pH 5.5 soil - goes counter to everything you read/experience. IMO, I wouldn’t worry about trying to change the soil pH. Just get her back on a normal feeding and maybe provide some shade at midday.

Hi Felipe! I agree it does seem odd that Greenhouse Seeds, in almost all of their grow videos, recommend soil pH levels lower than you might expect. I grew Arjan's Haze #1 and Arjan's Strawberry Haze last year, and both of those are said to like soil pH of 5.7. I remembered this only when the current problem arose, and quickly checked to see what the recommendation for Super Lemon Haze was, and it's 5.5.

Did your situation involve kelp meal? Or was it some other kind of nutrient overdose? Anyway, I guess you had the rust-brown edges on the leaves coupled with yellowing? Interesting that you had that in connection with heat stress. I guess I just brewed up a perfect storm this summer: too much kelp meal, too high pH, plus extreme heat. Never had that.

I'll continue to give her water at 5.5 going forward, not to change the soil but to improve her performance.

Be well,

Emeraldo

 

[FelipeBlu]

If I may ask, what is your soil? If it’s pre-buffered with lime, you don’t need to worry about pH.

 

[Emeraldo]

Yes, I use plenty of lime in mixing up the soil. But I used only half a cup per 15 gal pot this year, having added a whole cup last year. Also, I used kelp meal this year and may have added too much, since apparently kelp meal can drive up the soil pH.

 

[FelipeBlu]

As the plant takes in a K+ ion, it releases a H+ ion, which will react with the lime. If there isn’t enough lime, the pH in the medium will trend down (more acidic).

 

[Emeraldo]

Ok, and if there is enough lime, the pH goes up? Or would the pH tend to stay around 7?

I also was reading today that oyster shell will raise pH, and this year I put lots of that in, thinking it is a good calcium source.

 

[CO Finest]

Looks like two things to me. Burnt tips = nute burn mostly seen on lower big leafs first if newer leafs do not have burnt tips then the nute level is back down to where it should be. Second looks like possible high wind damage with browning being on one side of leaf and possible nute deficiency on other leaf by it self pic do to Ph levels. Heat problem you would see leafs looking like tacos. Cannabis like tomatoes cup leafs when sun gets to hot for them. As far as Ph I have used 65-68 sense 1986 not one Ph problem with hundreds of strains I have grown. If you swing your Ph to much you will see leafs twist which is sign of to much Ph swing. If your running bellow 6.0 in soil you are creating a deficiency.

 

[Emeraldo]

Thanks CO Finest for your experience.

I still need to measure the soil pH (lost my meter, ordered another), but I suspect it is maybe too high, around 7+. Will find that out in a few days.

But assuming the soil pH is in fact too high, wouldn't it make sense to water the plants with water that is pH'd lower? If the soil is 7.5 for example, could watering at 5.5 create a better environment for the roots? I'm thinking the lower pH of the water would compensate.

 

[FelipeBlu]

Ok, and if there is enough lime, the pH goes up? Or would the pH tend to stay around 7?

The pH will tend to stabilize where the lime balances the pH of the rest of the media. With some soils, this is designed to be between 6.5 and 7.

 

[CO Finest]

If I had your problem I would Ph A bunch of straight water at 6.8 and run it through aka flush. Then next time for water use straight water Ph at 6.8 not flush but regular feed amount and check run off. The good part about using soil is time is on your side unlike hydro game would be over.If you have kelp this would be a good time to give them after done to help with the stress and high temps. Kelp is key for growing in high temps hint of the day.

 

[FelipeBlu]

Thanks for that Jay. I didn't realize kelp meal has the effect of raising pH. I'll have to take that into account going forward.

I used kelp meal this year for the first time. Seemed like a good idea, rich in K. I got two 2 lb bags of Dr. Earth Kelp Meal for amending about 90 gallons of soil. In mixing it up, I noticed the amount of kelp meal in each bag was kind of skimpy and the first bag was used up so quickly I dumped in the second one as well. No wonder it comes in small 2 lb bags!

Could that amount of kelp meal raise the soil pH to the point that the Super Lemon Haze, which (according to Greenhouse Seeds) likes soil pH at 5.5, could experience a lockout? Possibly. Add the extreme heat in June, when it was up to 104F. The extreme heat causes the plant to use a lot of water, amplifying soil issues because potassium is a key element regulating the plant's ability to absorb and use water. So there are two good reasons for this leaf damage. I'll need to test the soil pH but lost my soil pH meter. Getting a new soil pH meter to do that. In the meantime, I'm flushing the SLH's soil with water @ 5.5.

Thanks again! It is starting to make sense now.

Looks like you already have kelp meal in the mix. I use silica to help the plants deal with heat and low humidity, but it’s a liquid amendment (Dyna-Gro ProteKt) that I add to the water.

 

[Emeraldo]

...
I don’t understand the recommendation to grow SLH in pH 5.5 soil - goes counter to everything you read/experience. IMO, I wouldn’t worry about trying to change the soil pH. Just get her back on a normal feeding and maybe provide some shade at midday.

Felipe, have a look at the Greenhouse Seeds grow videos, if you're interested. They're on Youtube. Here's the Super Lemon Haze session. The soil pH is consistently at 5.5 throughout the grow.

 

[Emeraldo]

Looks like you already have kelp meal in the mix. I use silica to help the plants deal with heat and low humidity, but it’s a liquid amendment (Dyna-Gro ProteKt) that I add to the water.

Yes, I added two 2-lb bags of Dr. Earth's kelp meal to my 90 gallons of soil when I amended this year, as a source of K. Now I'm hearing that it helps the plants deal with heat, and that it can raise soil pH. Never knew that.

I'll have to look into Dna-Gro ProteKt ( I take it the "K" is capitalized for a reason).