Red stems / phosphorous deficiency? Athena Pro line, Rockwool

flipflop64 · Apr 29, 2023

Hey guys, been a while since i lasts posted.
I am currently struggling with my plants in 4inch rockwool running Athena Pro Line at 3.0EC and 5.7-5.8PH.
I am using the classic "crop steering" irrigation strategy with about 8 waterings a day. My drain EC is 4.
They look phosphorous deficient for a couple days now. Red stem, some plants have purple hues on the backside of the leaves.

VPD between 0.7-0-9.
900ppm Co2
700ppfd LED lights (4000k + 460nm blue cree diodes). I am just vegging these plants in here.
Watering the Athena nutrient schedule at 3.0EC in RO water
Hypochlorous acid and their silicate "balance" product

Any athena users in here who add CalMag to the Pro Line? Athena rep told me CalMag def is impossible at 3.0EC.
I thought that they were rootbound first but all the smaller plants are affected too.

Should i transplant to more growing media?

flipflop64 · Apr 29, 2023

@Aqua Man Can you help out? You always seem to know whats going on

MIGrampaUSA · Apr 29, 2023

Disclaimer - soil grower

Red stems aren't always a P deficiency ... It can also be genetic or due to the stem being exposed to UV light. The one blemished leaf "could" be the first signs of deficiency ... but in hydro based grows I would think a P deficiency would show quickly. As for an EC of 4? I'll defer to the hydro wizards for more information ...

flipflop64 · Apr 29, 2023

MIGrampaUSA said:
Disclaimer - soil grower

Red stems aren't always a P deficiency ... It can also be genetic or due to the stem being exposed to UV light. The one blemished leaf "could" be the first signs of deficiency ... but in hydro based grows I would think a P deficiency would show quickly. As for an EC of 4? I'll defer to the hydro wizards for more information ...

All my 6 different strains are showing the same red stem. Also no UV light in the room.

MIGrampaUSA · Apr 29, 2023

flipflop64 said:
All my 6 different strains are showing the same red stem. Also no UV light in the room.

Then I guess we'll have to wait for @Aqua Man or one of the other hydro gurus.

I don't know this part for sure because I'm a soil grower, but I would expect if you were experiencing P deficiency due to lock-out or possibly inefficient amounts of P ... you would have more leaf necrosis than that one little blemish. The red stems still could be light related. Many grow lights have some UVA in their spectrum.

Dub_City405 · Apr 29, 2023

Did you check your par reading? The light intensity. Flush the plants for a day or two and then start up your feeding schedule again. PH levels could be off.

flipflop64 · Apr 29, 2023

Around 650ppfd. @Dub_City405 PH is around 5.8
@MIGrampaUSA My lights are custom made. There is no UV in the room .

mysticepipedon · Apr 29, 2023

Petioles (the stem from the stalk to the leaf) often turn red or purple, with exposure to strong light. It doesn't have to be UV.

Purple striped stems can also mean nothing, but again, I'm a soil grower.

Eledin · Apr 29, 2023

That happens to me all the time with different strains and in my case is because the temp fluctuates quite a bit at night and when the lights are off. Can be something else in your case, but they look healthy to me... do you have only a couple of tips like that or is it many? The tips could be just because of the high EC. Again, your case can be totally different to mine, just giving some info.

flipflop64 · Apr 29, 2023

Thanks for the answers. How long are you keeping plants in 4inch blocks?

Oldguy71 · Apr 29, 2023

Lower your ec by 10% and I bet it goes away

BudzAldrin · Apr 29, 2023

mysticepipedon said:
Petioles (the stem from the stalk to the leaf) often turn red or purple, with exposure to strong light. It doesn't have to be UV.

That's odd because I regularly have plants touching my lights and no purple up top. Yet the bottom 2-3 nodes are often purple, from before amending the soil... with phosphorus. And cranking the light intensity up. And drastically reducing the distance. And adding UV.

The leaf colors alone tells you it's -phosphorus. Cannabis leaves should be green not blue.

I'm not sure what crop steering entails in rockwool but every time it comes up I hear "dry backs" mentioned. Sounds like a racist term to me, but assuming you're letting your medium dry out at any point, take a look at this chart:

Now compare that to your nute profile and antagonism chart. Probably tons of Calcium and Magnesium. Calcium is what causes petioles to purple. By blocking phosphorus since it's still taken up when the medium is dry.

Growing in fiberglass doesn't make sense to me so this may not even apply, like how do you water something 8 times a day and steer anything? By letting it dry at night? I've never even seen a rockwool cube but it's definitely -P

flipflop64 · Apr 29, 2023

BudzAldrin said:
like how do you water something 8 times a day and steer anything? By letting it dry at night? I've never even seen a rockwool cube but it's definitely -P

Yea i've been thinking its P too. I will drop EC a bit and see what happens. Athena Pro line seems high in Ca.
Do you have any advise how to get rid of the phosphorous deficiency? Just drop EC?

Oldguy71 · Apr 29, 2023

A high phosphorus guano tea or top dressing, phosphoric acid to adjust ph, or a high phosphorus bloom additive all work

flipflop64 · Apr 29, 2023

Oldguy71 said:
A high phosphorus guano tea or top dressing, phosphoric acid to adjust ph, or a high phosphorus bloom additive all work

How can i be sure that its not just locked out by the high Cal from the 3.0 Athena?

flipflop64 · Apr 29, 2023

flipflop64 said:
How can i be sure that its not just locked out by the high Cal from the 3.0 Athena?

High transpiration rate causing the plant to take up too much Cal and locking out P and Mg? Athena is 150ppm Cal in the nutrient solution. I saw some Mg yellowing on some leaves earlier this week. Seems to add up.

Oldguy71 · Apr 29, 2023

I’m going by how dark green your plants are and 3.0 ec combined with red stems. 150 ppm calcium isn’t that high for cannabis especially in flower. When my plants get like that they are on the edge of lockout or just starting it. That’s why I think lowering your ec should clear it up

flipflop64 · Apr 29, 2023

Oldguy71 said:
I’m going by how dark green your plants are and 3.0 ec combined with red stems. 150 ppm calcium isn’t that high for cannabis especially in flower. When my plants get like that they are on the edge of lockout or just starting it. That’s why I think lowering your ec should clear it up

I'll start dropping EC to 2.6 :)
Thanks man i'll update in here

flipflop64 · May 4, 2023

So i lowered EC to 2.6 and they starting fading to a lighter green. I still have the purple stems and also the purpling on the underside of the leaves. Any ideas? Looks like phosphorus def to me. There is also this "tipburn". Its more like small brown dots appearing an the tips of the leaves.

flipflop64 · May 4, 2023

Red stems / phosphorous deficiency? Athena Pro line, Rockwool

Red stems / phosphorous deficiency? Athena Pro line, Rockwool

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