Leaf Burn when switching to Flower

Hey guys˜!
This is the 3rd time I have the same issue.
Can't point the problem.

The veg time is awesome, quick growth, no burns, amazing leafs:

As soon as 12/12 starts, leafs begin to burn, without any environmental changes:

Than goes downhill fast:

EC is 1.2, PH 5.8, straight coco.
Temps 27C, RH 70%, good VPD.

Jacks 321 with RO water.

The lighting is a custom DIY panel with 2x Phantom Boards @ 2 amps, 10x Clu048 1212 cobs 97CRI @ 1 amp.
Everything dimmed down to around 30.000 lux.
Sealed room with CO2 only dispensing enough to maintain around 500ppm, not boosting. Exhausting 15min every 2 hours.

I don't know what to do...

I've noticed this also while growing in coco with RO and Jack's 321. I believe it's due to potassium and calcium deficiency so I've been supplementing with biomin calcium and mono ammonium phosphate while decreasing calcium nitrate. Yield has increased by around 50% but the deficiencies are still cropping up which leads me to believe pot size could be an issue.

kunkgrow said:

Hey guys˜!
This is the 3rd time I have the same issue.
Can't point the problem.

The veg time is awesome, quick growth, no burns, amazing leafs:
View Image
As soon as 12/12 starts, leafs begin to burn, without any environmental changes:
View Image
Than goes downhill fast:
View Image
EC is 1.2, PH 5.8, straight coco.
Temps 27C, RH 70%, good VPD.

Jacks 321 with RO water.

The lighting is a custom DIY panel with 2x Phantom Boards @ 2 amps, 10x Clu048 1212 cobs 97CRI @ 1 amp.
Everything dimmed down to around 30.000 lux.
Sealed room with CO2 only dispensing enough to maintain around 500ppm, not boosting. Exhausting 15min every 2 hours.

I don't know what to do...

Click to expand...

The plants are alive. Don't sweat it. They can grow out of this.

You have a mobile nutrient deficiency at the start of flowering.

That's usually magnesium (Mg) or phoshorus (P).

In your case because of the R/O water, magnesium deficiency is very likely, because R/O takes both magnesium and calcium out of the water.

At flowering, the plant is looking to expand it's root system. To support all those new calyxes and hairs, it needs a substantial expansion of the root system. That's why it needs phosphorus, because that's the stuff roots are made of. And a little root stimulator goes a long way, however it's not necessary.

In hydro, you don't have to think about repotting at this stage, or topping up with new soil which also works great because cannabis can grow roots from it's stem.

What I have found works very well, is to take a pinch of magnesium lime, put it in a quart of R/O water for at least a day, and then mix that (no residue) with untreated R/O water at a rate 1:3, or a quarter of the entire nutrient solution. That worked a lot better than a cal/mag supplement I bought.

UPDATE

It's the R/O water and flowering combination that creates magnesium deficiency.

Good point on the magnesium, although the 321 recipe already includes 1 gram per gallon of MgSO4. In my case some plants tend to use more calcium. I saw the wrinkled leaves in the second picture which could be a mild calcium def, but it's probably mainly a phosphorous issue. Keep in mind that coco formulated nutes have slightly higher levels of phosphorous than Jack's.


Canna Coco A+B: 4 - 4 - 3
Hesi Coco: 3 - 4 - 5
Jack's 321: 3.75 - 2.4 - 5.2

rjrom90 said:

Good point on the magnesium, although the 321 recipe already includes 1 gram per gallon of MgSO4. In my case some plants tend to use more calcium. I saw the wrinkled leaves in the second picture which could be a mild calcium def, but it's probably mainly a phosphorous issue. Keep in mind that coco formulated nutes have slightly higher levels of phosphorous than Jack's.

Canna Coco A+B: 4 - 4 - 3
Hesi Coco: 3 - 4 - 5
Jack's 321: 3.75 - 2.4 - 5.2

Click to expand...

What convinces me that it's magnesium, is that:

- The damage is very uniform, so we're not talking about a combination of deficiencies or lockouts
- The damage is from a mobile nutrient deficiency, starting with the middle leaves and working it's way to the top
- The damage pattern of the leaf is that the tip is affected first, followed by the edges of the leaf.
- Damage from calcium deficiency looks very different, with mottled spots across the leaf, and the damage tends to not move up the plant.

https://www.growweedeasy.com/calcium-deficiency-cannabis

Yep, Mg.

When you transplant, do you leave it in the dark for a time? Or, perhaps, do your plants take a long time between feedings/(drinking slowly) during this weird phase?

Maybe too much Mg?

I've seen a lot of growers NOT use the 1 part in the 321 combo unless they are experiencing a Mg issue.


I'm interested in where this thread goes. I just purchased Jacks + Cal-nit.

My apologies for the misdiagnosis. I just observed some OG/chem varietals on the 321 recipe that are showing mag defs simliar to the OP pictures. I was under the impression that the Jack's 321 recipe was intended for RO whereas magnesium supplementation was unneeded for most tap water. However some plants seem to need a bit more magnesium. I will try 1.5 grams per gallon MgSO4 and see if things improve.

Yeah I'm with mj on this. It's too much perhaps. It's an imbalance of N:mg and then after Ca:mg and then K:mg. Let them really get on a dry cycle before you start more frequent watering again. Your mg may be inhibiting some sites and they need to be expended