Phosphorus deficiency


My plant appears to have a serious phosphorus deficiency. It came on very rapidly & has progressed to the point that about 75% of the leaves are affected. It is about 10 wks from germination so several weeks til harvest. Should I remove all the bad leaves? I’ve checked PH of water- it’s around 6.5, have flushed with plain water & also flushed with bloom nutrient , don’t know what else to do?
Thanks for any advice!
Mari :sob:


Pictures would be great also more info. Are you sure it’s not nute burn? How offen you feeding? It could be a few things


If your only two web’s from harvest I myself wouldn’t worry about it.



I compared to pictures of phosphorus deficiency & looks pretty much like what my plants are suffering from. One is worse than the other. Should I remove all the bad leaves? Most of the upper fan leaves are very badly affected & also alot of the smaller ones too. Should I go ahead & start the harvest or wait another week or so. The other one is a few weeks behind & not as bad but time will tell. I checked the ph of runoff today & it was close to 7.
thanks for any suggestions!


I followed the feeding schedule of weekly, using Fox Farms & usually use less than suggested. It’s strange the other 3 never showed any sign of these problems. All planted the same.The only difference was I brought them inside to a closet while drying the others in the shed- about a week.
Mari :sweat:


Like I said it could be a few things. Need some pictures Nute burn kinda looks like phosphorus deficiency in later stages to me. I would wait to harvest.
COPY/PASTE: This “Support Ticket” into your forum post.
Answer these simple questions the best you can.
If you do not know, or do not use something; Just say so = NA

Strain; Type, Bag seed, or NA

Soil in pots, Hydroponic, or Coco?

System type?

PH of runoff or solution in reservoir?

What is strength of nutrient mix? EC, or TDS

Indoor or Outdoor

Light system, size?

Temps; Day, Night

Humidity; Day, Night

Ventilation system; Yes, No, Size

AC, Humidifier, De-humidifier,

Co2; Yes, NoZ
@MacGyverStoner hopefully will chime in.


Everyone makes the same mistake. Each plant is different from the other. That’s why some will be doing just fine while a couple of others of the same strain won’t be. And have to be treated differently.
I’m going through the same thing only it’s PH two plants 5.0 and three others 7.0 same soil same amount of nutrients…don’t figure! I just deal with each plants needs



Strain; Type, Bag seed, or NA

Soil in pots, Hydroponic, or Coco?

System type?

PH of runoff or solution in reservoir?

What is strength of nutrient mix? EC, or TDS

Indoor or Outdoor

Light system, size?

Temps; Day, Night 77-80

Humidity; Day, Night 45-48

Ventilation system; Yes, No, Size 4" intake, 6" Ventifan( scrubber/Phresh filter)

AC, Humidifier, De-humidifier, No AC, de-humidifier yes

Co2; Yes, NoZ No CO2


Sorry forgot this part- thanks !!

Strain; Type, Bag seed, or NA ILGM auto Northern Lights

Soil in pots, Hydroponic, or Coco? Fox Farms Ocean Forest

System type?

PH of runoff or solution in reservoir? PH runoff 6.5

What is strength of nutrient mix? EC, or TDS Fox Farms,

Indoor or Outdoor Indoor/Grow Shed, 1 week inside closet

Light system, size? T5/CFL


Your plants look just like mine.
I’ll bet the farm PH is out of range.
My plants do have a lot of yellow also… Nearly all flowering nutrients will come with an abundance of phosphorus for your plants. So if you’re seeing a cannabis phosphorus deficiency while using standard cannabis nutrients, chances are you actually have a root pH problem.,
phosphorus is best absorbed by the roots in the 6.2 - 7.0 pH range (in soil, it’s generally recommended to keep the pH between 6.0 - 7.0, but phosphorus specifically tends to be best absorbed above 6.2 and below 7.0)hosphorus is used heavily by cannabis plants in the flowering phase to produce buds, and is a crucial component of photosynthesis (turning light into energy for the plant).
Some strains of cannabis use much more phosphorus than others, or be more susceptible to a phosphorus deficiency, and you may have many plants in the exact same setup with only some of the plants showing signs of a phosphorus deficiency.
Remember what I said about plants?
, flush your system with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients that includes phosphorus. This will remove any nutrient salts that may be affected the uptake of phosphorus and help restore pH to the proper levels.

I hope this help you out Marichan

B Safe


I flushed with just water, then I flushed with the fox farms nutrient(Big Bloom) that was a few days ago, one plant is worse than the other but I guess I’ll just ride it out until next week or so. I think it really affected the plant overall cause it is small & not as dense as it should be. Good learning experience anyways.
Thanks for all the input, appreciate it all!


You keep ignoring the question, what is the TDS or EC in the soil, in the root-zone? This is where your problem is probably coming from.



Also, if you are putting 6.5 pH water in the top, but 7.0 is coming out the bottom of the soil, that means your soil might be as high as 7.5. This is why we need the pH and TDS of everything, the water, the nutrient mix and water when you feed it, and the run-off that comes out the bottom, pH and EC/TDS/PPM are all important to know.



You are absolutely right MacG!
Just tested the soil in several places and it ranged from mid to high 7. Just flushed again with plain water, anything else to do?
Barely has any good green fan leaves on top, very few on bottom, so sad.


You had bud rot before, and I’d be worried about mold or fungi on your leaves too. I think I might see some in some of those pictures. It is real hard to say what to do so late in the game.

Again, knowing how strong the nutrients have built up in the soil with testing the total dissolved solids or electrical conductivity in parts per million, the strength in the run-off, would be a big help in letting us know what to do next.



Ph in runoff is about high 6-7 range now. As you stated it’s pretty late in the game. I didn’t see it coming, they were looking so green & healthy - then all of a sudden like over night the leaves turned.


I am not asking for the pH, we need the EC TDS.


I’m sorry but have no idea how to test for those(EC, TDS) all I have is a ph tester for soil & one for water but sounds like something more complex?
Being a total newbie & un-knowledgeable about growing has been quite a process, appreciate your expertise as always!
regards, Mari


Check it out:

Robert’s youtube on testing soil:

Robert’s blog on testing soil:



Thanks MacG! So all I really need is to get this Mudder TDS meter to do regular checking of the plants soil. Looks simple enough but what to do to correct the problem?