Potassium Deficiency? What Do You Think?

[Honestfarm]

Hello all! It’s my first time growing cannabis. I’m growing indoors in a 50/50 peatmoss/perlite mix amended with some homemade compost, ewc, alfalfa, kelp, gypsum, dolomite lime, neem, azomite. This mix was allowed to cook for a couple weeks before use. The only synthetic thing I’m about to start using is some mono potassium phosphate for flowering. Also sprayed some with baking soda solution if you’re wondering what the white stain is.

Most of my plants look solid with little discoloring or issues. These first 2 pictures show this.

However the last 3 pictures here show the issues with 2 of my LA Cakes. It has rapidly browning leaves under the canopy that turn crispy within a day or 2. It’s starting to frustrate me as my other plants look nice and I am about to flip to flower.

Any suggestions on what this browning could be? I figured it could be potassium deficiency (so the MKP should help) but I’m wondering what you guys think. Any suggestions are welcome!

 

[Homesteader]

Baking is sodium bicarbonate and not too good for your plants. Not too sure what is going on but I would clean up the dead leaves and stop using mono potassium phosphate. Nutrients interact with each other fairly easily and its easy to get things out of whack by having too much of one which will throw off another.

 

[Honestfarm]

Baking is sodium bicarbonate and not too good for your plants. Not too sure what is going on but I would clean up the dead leaves and stop using mono potassium phosphate. Nutrients interact with each other fairly easily and its easy to get things out of whack by having too much of one which will throw off another.

Okay so what do you think is my deficiency here then with the browning leaves?

 

[Homesteader]

Could be caused by the salt or an imbalance of nutrients. How long have you been spraying it with baking soda?

 

[Honestfarm]

Just did about 3 times after I saw a little pm per recommendation of a handful of other growers I’ve asked. pH of soil run off is about 6.6 so we should be good for lockouts and stuff. I’m thinking it’s a deficiency of some kind just have to find out which one.

 

[crimsonecho]

Just did about 3 times after I saw a little pm per recommendation of a handful of other growers I’ve asked. pH of soil run off is about 6.6 so we should be good for lockouts and stuff. I’m thinking it’s a deficiency of some kind just have to find out which one.

Potassium bicarbonate is better than sodium bicarbonate for pm, because it doesnt contain sodium.

 

[Honestfarm]

Potassium bicarbonate is better than sodium bicarbonate for pm, because it doesnt contain sodium.

Okay thanks I will do that in the future. Any advice about the browning leaves and what deficiency that might be? I’m decently sure it’s unconnected to the spraying as that just started and the browning has been occurring for 1-2 weeks.

 

[crimsonecho]

Okay thanks I will do that in the future. Any advice about the browning leaves and what deficiency that might be? I’m decently sure it’s unconnected to the spraying as that just started and the browning has been occurring for 1-2 weeks.

I’m not great at diagnosing deficiencies. I usually give my plants good, rich mix and if deficiencies occur, i do a full feeding or top dress with wormcasting mixed with a little bit of bat guano. Kinda looks like phosphorus to me..

 

[Honestfarm]

I’m not great at diagnosing deficiencies. I usually give my plants good, rich mix and if deficiencies occur, i do a full feeding or top dress with wormcasting mixed with a little bit of bat guano. Kinda looks like phosphorus to me..

Thanks yeah I’m thinking either P or K deficiency but I’ve also heard that it could be magnesium. A few different opinions on different forums. I’ll just experiment and see what happens I suppose

 

[Homesteader]

Mulder's chart shows how nutrients interact. If anything, its Phosphurus but that doesn't necessarily mean you are short on it. It could just mean that you have too high of another nutrient. It is fairly complicated but here is the chart. Phos negatively reacts with several other nutrients. This chart should not be used to chase deficiencies though and instead to understand how they react. Look at phosphate and follow the red lines from it. Copper, Calcium, Potash, Iron and zinc all can be screwed by having too much phos and its hard to pinpoint. You will also see that magnesium has a green line going to it, thats because high amounts of phos help mag uptake. I personally would go WATER ONLY until you get your soil mix down.

 

[Honestfarm]

Mulder's chart shows how nutrients interact. If anything, its Phosphurus but that doesn't necessarily mean you are short on it. It could just mean that you have too high of another nutrient. It is fairly complicated but here is the chart. Phos negatively reacts with several other nutrients. This chart should not be used to chase deficiencies though and instead to understand how they react. Look at phosphate and follow the red lines from it. Copper, Calcium, Potash, Iron and zinc all can be screwed by having too much phos and its hard to pinpoint. You will also see that magnesium has a green line going to it, thats because high amounts of phos help mag uptake. I personally would go WATER ONLY until you get your soil mix down.View attachment 852662

Thanks for this! I’m diving more into the rabbit hole of these nutrients and their relationships. I think an excess in Ca (I have gypsum and dolomite lime in mix) might be strangling phosphorus and some other nutrients. Going to try to cut down on Ca for the next mix. Not too sure how to mitigate this problem with the plants already in containers and Scrog though. I guess just experiment and hope for the best for them.

 

[Homesteader]

I am not a fan of dolomite because of the excess mag and the carbonates are not helpful. Too much magnesium in your mix will lock out calcium quite easily. Gypsum is much better but too much will cause a nasty sulfur flavor in your finished product.

 

[Homesteader]

Dr Harry Mills did studies with dry weight % in tissue analysis on various strains of cannabis that show 10%+ is calcium, 3%+ is Nitrogen, Potassium 3%+, Silica 3%+, Mag .8%, Phos .4% and sulfur .2%......This goes to show you how important calcium is.....and if you are wondering how that adds up, Carbon is very very high as you can imagine. Just keep this in the back of your mind when adjusting your mix.
Here is a link to Dyna-grow. Ive never used their products and probably never will (nothing against them) but the information is a good source and its free.
https://dyna-gro.com/calcium-and-its-role-in-plant-health/

The other thing to remember is that calcium plays a vital role in the health of your soil. Too much magnesium makes the soil compacted and tight but calcium is a large molecule and allows air space, which is why gypsum is often referred to as a soil conditioner. It allows roots to thrive by allowing them to breathe easier.

 

[Honestfarm]

Dr Harry Mills did studies with dry weight % in tissue analysis on various strains of cannabis that show 10%+ is calcium, 3%+ is Nitrogen, Potassium 3%+, Silica 3%+, Mag .8%, Phos .4% and sulfur .2%......This goes to show you how important calcium is.....and if you are wondering how that adds up, Carbon is very very high as you can imagine. Just keep this in the back of your mind when adjusting your mix.
Here is a link to Dyna-grow. Ive never used their products and probably never will (nothing against them) but the information is a good source and its free.
https://dyna-gro.com/calcium-and-its-role-in-plant-health/

The other thing to remember is that calcium plays a vital role in the health of your soil. Too much magnesium makes the soil compacted and tight but calcium is a large molecule and allows air space, which is why gypsum is often referred to as a soil conditioner. It allows roots to thrive by allowing them to breathe easier.

Thanks so much for the info. Keep it coming. I definitely think figuring out the calcium/magnesium dynamic is potentially my issue here.

 

[Kot]

I do not see potassium deficiency. I see purple stems, which might be phosphorus deficiency.