Autoflower week 9: light stress, calMag or natural fading ?

Hey brothers, I am finishing this CBD Fix auto soon but it started fading one week ago. It is 60 days old today and should be ready in around 2 weeks, max 3 weeks.

The fading is more in the upper fan leaves which makes me think about light stress. The ppfd is 600-650 at the top of the canopy, it doesn’t sound too much to me tho.
Popcorn buds remain unaffected and lots of fan leaves are still normal green.

Doesnt it looks like a calMag deficiency ?

Regarding soil, I am using following recipe:
- 7 gal fabric container
- used biobizz light mix
- 15% EWC + biochar
- 1 cup rock dust
- some pumice

The nutrients are dry fertilizer from Green House Feeding. I mixed 60g Bio Grow (7-2-4) with the initial soil and top dressed ½ cup (80g) GHF Bio Bloom (4-9-9) 3 weeks ago. It has 8% Ca and 4% Mg in it.
Otherwise only things I did was giving her 4 tbsp dolomite at the end of veg and water with kelp/ humic acids every 2 weeks.

3 days ago I gave it 3L tap water mixed with epsom salt (1 tsp), molasses (2 tsp) and 8 ml organic liquid fert 2-2-5. No visible improvement.

The environnement:
Day: 25*C/ 45-50%
Night: 19*C/ 55-60%
LST: 1.5 *C colder than room temp
VPD: 1.2-1.3
Light: 18/6
Soil moisture between 18% and 35% VWC, 2L every 3 days.

What do you guys think ? Deficiency, light or just natural senescence near the end ?
The buds looks good tho, super smelly

Lighting could be more neutral but looks like early magnesium deficiency. Don’t see any calcium deficiency but considering the stage of flower calcium and magnesium demand is high. Wouldn’t hurt to give a dose.

What do you mean by more neutral ? Less intense ?

Magnesium is what I suspect because of the inter-veinal chlorosis but not all the leaves are showing this symptom, weird.
I gave it some epsom and molasses, hope it helps a bit. I won’t be at home for 6 days so she will only become plain water through drippers until I come back.

Funny, this leaf is half healthy, half sick

Either magnesium or manganese def from what I can see. They look very similar to start but with a slight difference. One is mobile the other is not.

Since it’s affecting your top growth I’m inclined to say it’s manganese. Can stop it progressing by adding 1g of manganese sulphate per gallon every other feed until last 3 weeks of flower.

Yours still have a good 3 more weeks to ripen

Thanks for the help. I wasnt suspecting manganese indeed. Can it be locked out by anything ?

Slurry test says 6.9 (probably the dolomite) and 380 ppm

Did some research about Mn def but I can’t see a single brown spot on the leaves. Maybe it will happen later. Stay tune…

juansensor said:

Thanks for the help. I wasnt suspecting manganese indeed. Can it be locked out by anything ?

Slurry test says 6.9 (probably the dolomite) and 380 ppm

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Can be locked out by excess calcium or iron. The dolomite is not helping either and could be the cause. You’re best mixing the lime at the start and waiting minimum 4 weeks for it to settle, otherwise it can cause a lot of issues

Brown spots happen later.

If this is as you say I cannot do anything.

I run into the same issue with half of my grows and it makes me insane, i am beginning to lose hope!
How is it possible that this happens even with quality soil/ nutrient at right amounts, perfect conditions in the tent, ppfd in check, added microbes every 2 weeks…. I don’t get why they get so bad so often.
I am using tap water 300 ppm. 90 ppm Ca and 9 ppm Mg. Should I supplement Mg to my irrigation water to prevent this to happen ?

please help me!

juansensor said:

I run into the same issue with half of my grows and it makes me insane, i am beginning to lose hope!
How is it possible that this happens even with quality soil/ nutrient at right amounts, perfect conditions in the tent, ppfd in check, added microbes every 2 weeks…. I don’t get why they get so bad so often.
I am using tap water 300 ppm. 90 ppm Ca and 9 ppm Mg. Should I supplement Mg to my irrigation water to prevent this to happen ?

please help me!

Click to expand...

Are you liming every time?

High organic matter makes manganese less available as well!

Did you try Epsom salts to fix the problem before?

Actually I only use dolomite when the pH is on the low end of the desired range.
But I have heard from farmer to add some dolomite (CaCO3) with nitrogen fertilizer to buffer acidity. Not sure about that but sounds legit as nitrogen mineralization produces H+

If the pH is in the range, I would use Gypsum. Now I am thinking about adding epsom salt every time I use gypsum because the water I use has low magnesium.

I tried epsom salt @ 1 tsp/ gallon to try to fix the issue but couldn’t see any improvement. Maybe this was not enough.

Just before leaving for Christmas traditional family visit, I gave the plant 3L water with:
- 2 tsp blackstrap molasses
- 2 tsp epsom
- 2 tsp cellmax organic bloom 2-2-5
- 3g greenhouse feeding Enhancer with kelp

I’ll be back on Wednesday and see how the plant did alone…

I didn’t know too much organic matter could create problems!!
i see people using huge amount of worm casting in their recipe, sometimes up to a ⅓ of the mix