Questions on possible magnesium deficiency

[Forester]

Hi guys,

I've got an Auto White Widow going on her third week.
At about 14 days I started to notice the leaves (mostly one, oldest) was getting deep dark green in one spot.
Soon after that, the area turned lime green/yellow. Now, a few days later the area is about the same, but new growth is also affected.
Also a few spots on the first leave, yellowing.
Plant seems to be doing good otherwise, visible new growth every day.

I'm growing under 60W COB LED, Hs40 tent (1.3x1.3f)
Temp: 23
RH: 50
Medium: Organic Soil, 7.5l pot
Watering: Twice every 24/h of a total 0.15 liters.
Ph: 5.5-6.5
Irrigation water PH: 7

I got suggestion that this might be a magnesium deficiency, so...

My soil mix has 154 magnesium /liter soil.
Most plants do well with like 20 - 50 ppm as far as I understood it, but can't seem to get a number of how much cannabis demand. Just that it is a heavy feeder.
Anyone got any numbers there?

That leads me to think that if it is a mag. deficiency, maybe it's caused by a lock-out? Since there should be enough in the soil (or maybe not).
I am thinking of spraying a foliar of Epsom salt to see what that does.
If it's a lock-out, a foliar should get around this giving the plant the nutrients another way than the roots, right?

Also, the typical signs of magnesium deficiency seems to be that the veins stay green, which is not really the case here. Maybe it's something else?

 

[Aqua Man]

Tad to much light and of you watch that bottom leaf will likely droop and touch the soil starting around lights out and over night... I have a feeling that's where the damage is from

 

[Marzcanna]

Just to add to what @Aqua Man already said, From the ph ranges you described i would try to keep it more consistent around 6.3-6.5 most waterings especially for calcium & magnesium uptake. Organic Soil should have a natural ph buffer but i have had issues with it using ph 7.0+ and anything below 6.0ph. But that could of been my bad soil mix at the time aswel

 

[fishbuds]

Just to add to what @Aqua Man already said, From the ph ranges you described i would try to keep it more consistent around 6.3-6.5 most waterings especially for calcium & magnesium uptake. Organic Soil should have a natural ph buffer but i have had issues with it using ph 7.0+ and anything below 6.0ph. But that could of been my bad soil mix at the time aswel

I think you got it. Young plants seem to like ph in the lower to mid 6's, and progressively increase to 6.5 - 6.8 throughout the grow, in soil.
after feeding 6.8 for week 7 flower, I will drop to 6.4 for the ripening flush, to ensure plenty of calcium is available as she finishes.
.02

 

[Aqua Man]

Should add possible watering issues

 

[Forester]

Should add possible watering issues

Magnesium deficency, caused by a watering issue, or yellowing caused by watering issue?
Overwatering?
I've really tried not to overwater, and I give it a total of 1,5dl of water/24 hour.

 

[Aqua Man]

Magnesium deficency, caused by a watering issue, or yellowing caused by watering issue?
Overwatering?
I've really tried not to overwater, and I give it a total of 1,5dl of water/24 hour.

Maybe under maybe over... hard to tell as they look ok now. Either will cause nutrient uptake issues and show deficiencies

 

[Forester]

Thanks for your input. Very appreciated.

I raised my light to 50 cm above, it was before on 40. I lowered it maybe a week ago, since I thought I started to get a bit too much stretch.
Manufacturers distance chart says 50 cm.

And I will get some epsom salt any day now and give it a foliar spray.
Hopefully this will resolve the issue, but will keep a close eye on new growth.

And any day now I will start to go into another watering phase (lil bit more water), so will see what that does too.

 

[growsince79]

Thanks for your input. Very appreciated.

I raised my light to 50 cm above, it was before on 40. I lowered it maybe a week ago, since I thought I started to get a bit too much stretch.
Manufacturers distance chart says 50 cm.

And I will get some epsom salt any day now and give it a foliar spray.
Hopefully this will resolve the issue, but will keep a close eye on new growth.

And any day now I will start to go into another watering phase (lil bit more water), so will see what that does too.

How big is that container? Sounds like you water too little to often.

 

[Forester]

How big is that container? Sounds like you water too little to often.

7.5 liter/2 gallons
Watering twice a day, 0,5-0,75dl each time.

 

[Aqua Man]

How big is that container? Sounds like you water too little to often.

That's the right question right there.

 

[growsince79]

7.5 liter/2 gallons
Watering twice a day, 0,5-0,75dl each time.

Yeah thats the problem. You need to slowly water to saturation/ runoff every time you water. Depending on the soil that would be at least 2 liters every 3-4 days.

 

[Forester]

I overwatered my last grow which eventually led to the complete demise of that poor girl.
Trying to avoid walking down that same path again, I found this, and has been following that scheme.

So far, hasn't moved beyond the spray bottle.

 

[Forester]

Yeah thats the problem. You need to slowly water to saturation/ runoff every time you water. Depending on the soil that would be at least 2 liters every 3-4 days.

Today I gave her a foliar spray of Epsom and also started new water regiment. I held off watering yesterday and for the first time I watered the whole medium today. I gave two cups of water, slowly. Even got a bit of runoff from that just as I finished.
Will wait a few days, until medium is dry, before watering again. Expecting that to be several days.

Now we shall see how she responds to these changes.
There's a bit of lime green/yellow spots on some of the new (not the latest) leafs, hopefully any new growth will be nothing but green.

Thanks again for all the input.

 

[Jethrowfromdethrow]

Today I gave her a foliar spray of Epsom and also started new water regiment. I held off watering yesterday and for the first time I watered the whole medium today. I gave two cups of water, slowly. Even got a bit of runoff from that just as I finished.
Will wait a few days, until medium is dry, before watering again. Expecting that to be several days.

Now we shall see how she responds to these changes.
There's a bit of lime green/yellow spots on some of the new (not the latest) leafs, hopefully any new growth will be nothing but green.

Thanks again for all the input.

Hey bro! I’m experiencing the same issues and wanted to see how the foliage spraying and the watering regiment helped. How did it go?!