Magnesium deficiency

Need some help on this one.

Peat based media
50:50 bloom/grow organic feed 1/4 strength (contains no cal/mag)
Recently added an organic cal/mag 1/2 strength
Watered every 2 days (soil gets nice and dry and no watering issues in her life)
600w mH in air cooled hood 18’ away from the tops.
Humidity 45%
temp 70-77


I have a 7 week 5 day old auto which for the past couple weeks has being showing signs of a magnesium def. Only really effecting the middle section of the plant. Leaves feel
Dry and stiff in places. Also the leaves in the middle getting most of the light are much more yellow but not really interveinal?

Ive been giving 1g per litre so just under 1tsp per gal of Epsom salts. Can I give her more? Like 2g per L?

It initially slowed down but now it’s picking back up.

I have really soft water 36ppm with basically no mag and have been adding a little calmag to give me a base before my nutrients. served me well on the other plants but this one seems to want more magnesium?

It’s not pH related as I’ve tested the soil with a trusted pH probe . Pot temps stay around 19-22c so not that. I just think she wants more? No other deficiencies which you usually get when the pH goes out of balance. What you guys think?

Cheers!

Drop the grow nutes maybe.

What's the strain?

Ph probes kinda suck , do a slurry test on your soil to find out the ph at the root zone

Also remember although soil is a great buffer of ph. It also reacts much slower to correction of deficiencies. next time use cal mag the entire way especially if your municipal water supply has low ppm water at under 30ppm it’s almost RO water. I stop using cal mag at week 5 flower though.

CannabisErecticus said:

Ph probes kinda suck , do a slurry test on your soil to find out the ph at the root zone

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This one is pretty damn good!https://aperainst.com/ph60s-premium-spear-ph-meter-pocket-tester-for-solid-semi-solid-sample-ph-measurement-cheese-meat-sushi-rice-soil-canning

All the others are happy and have the same pH so that’s why I’m leaning towards not enough?

@mistergrafik It’s A blue dream auto by fastbuds. Have been alternating 50;50 and pure bloom. Backed off the full bloom as K and P mess with Magnesium.

if it was cheaper I would try it but I’ve found although time consuming a slurry test using distilled water is the best way to measure root zone ph, I purchased a blue labs soil probe and a generic soil probe and neither were worth a damn. Hope that one is better than the ones I’ve used.

CannabisErecticus said:

if it was cheaper I would try it but I’ve found although time consuming a slurry test using distilled water is the best way to measure root zone ph, I purchased a blue labs soil probe and a generic soil probe and neither were worth a damn. Hope that one is better than the ones I’ve used.

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Got distilled water so will try and see. But I’m just curious if I can simply add more?

Water day tomorrow and I’m going to up the dosage. If it doesn’t get better then I’ll simply flush and give a balanced dose of nutrients.

Make sure you lightly dig an inch or two being careful not to damage feeder roots. 1 part soil 1part distilled water stir for 1 minute let sit for 5 come back and measure

I wouldn’t flush this far along in flower, they are looking nice. I think you could ride it out and still have a nice harvest

I use 1 TBLS per gallon on the Epsom. Not sure how that breaks down for you. I would start with that especially since you’re showing def.

CannabisErecticus said:

I wouldn’t flush this far along in flower, they are looking nice. I think you could ride it out and still have a nice harvest

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Cheers for the info - will do that tomorrow. Yeah flushing is always a last resort so going to see if I can help them by simply upping the dosage. I’ve got no pH up on hand and haven’t needed it cause the microbes are everything to me in this grow.

@Wattzzup 1tbsp is 15g. US gallon I think is 3.8l? So roughly 4g a L... yeah I’m way out if that’s anything to go by. Since I’ve held it at bay for a while and I know magnesium is present maybe double the dosage to 2g? Then if no sign of improvement a final 4g dose? She was on bloom for a while which seem to exaggerate the def.

I always refer to this chart for guidance. NPK and Ca all interfere with Mag...

I would hit one time with a good amount and watch it change over a few days. Continuing to under feed and expect results seems silly to me.

Epsom ppm and other

Any pests? I’ve seen root aphids cause damage that looks exactly like a magnesium deficiency.

If your ph is fine and you have no soil pests definitely add a little more Epsom salts, I like to foliage spray with epsom but obviously you can’t that far into flower

CannabisErecticus said:

Any pests? I’ve seen root aphids cause damage that looks exactly like a magnesium deficiency.

If your ph is fine and you have no soil pests definitely add a little more Epsom salts, I like to foliage spray with epsom but obviously you can’t that far into flower

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No pests as far as I’m aware. I inspect the soil daily and don’t see anything on the soil or leaves etc. As I mentioned before the other plant in the same maturity is doing just fine although is smaller and requires less food.

@Wattzzup I lowered the PK to see if it was too much messing with the uptake of magnesium and to rule out nitrogen. Now I’ve turned to increasing the magnesium.

Nice chart wood! So looks like 1g per a L is about 104ppm of magnesium? Don’t know if this is enough :/

Many of us have dealt with Mg Deficiency...just as many have caused this ourselves.

Mg is the one nutrient that can lock itself out if too much is in the soil
So be very careful adding Epsom Salt (Magnesium Sulfate) , Langbeinite (0-0-22 with high Mg) and Crab Meal (high calcium) to your soils.

Chasing a mag deficiency is one the most frustrating things in growing - because we see a plant deficiency when in fact it is an excess of Mg causing the problem. Or excess of K or Cal.

@Nutty sKunK, the attached .pdf holds many valuable infos about the interactions of K:Ca:Mg.

The plants with the yellow top fanleaves are much more remniscient of an Sulfur def than Mg, as this resembles more a N-def, just starting from the middle or top of the plant, whereas NPK Mg defs start lower.

Hope this helps

Kassiopeija said:

@Nutty sKunK, the attached .pdf holds many valuable infos about the interactions of K:Ca:Mg.

The plants with the yellow top fanleaves are much more remniscient of an Sulfur def than Mg, as this resembles more a N-def, just starting from the middle or top of the plant, whereas NPK Mg defs start lower.

Hope this helps

Click to expand...

Nice info there! Yeah you’re right. I was under feeding them so it was a lack of K,mg and N in the end.

Was feeding 2ml per L now I’m at 3ml bloom + 1ml grow and it’s just enough to sustain. Increase 1ml every feed to find that sweetspot.

This plants 70 days old and hasn’t nearly faded as much as the others. Pretty new to these nutrients.