Leaf darkening mystery I can't figure out

[plan500]

The other day I was looking up the general amounts of Phosphorous and Potassium flowering plants will need for their flowering stage. I was looking at not just Cannabis but also the popular vegetable plants and flowers grown by home gardeners. What I noticed was more recommendations to start applying at the very start of the flowering period instead of the past recommendation of applying after the start or when full flowering is taking place.

This is one step I already took, as I now use the Alga Bloom the moment I flip them to 12/12 instead of a week or two later.

 

[plan500]

If you have signs of overfeeding that you don't like, why not just feed less? Problem solved!

Minerals accumulate in the medium and depending on your amount of runoff and feeding frequency it may add up in mid flower? From what I see you have two options, you can do is either feed less or increase runoff to better replenish the medium.

It's all about feeding strength and making the nutrients available and in range for optimal uptake by managing pH. I've seen many people including mods and reviewers on her giving the advice to add more minerals upon a already complete plant food. Most plant related problems are pH related in nature since we all more or less use a complete plant food with good mineral ratios. You can band-aid all problems which is a sub par practice. If you already have 150ppm per gallons of K in the mix and only 20% of it being accessible to the plant you don't solve anything by adding more, you're just masking the main problem and end up with other deficiencies.

I have tried feeding less, in different scenarios, if fact I starved a couple of grows to try and prove that point. Plants still got dark and eventually yellowed with burned tips (not from nute burn but from hunger).

 

[Wastei]

I have tried feeding less, in different scenarios, if fact I starved a couple of grows to try and prove that point. Plants still got dark and eventually yellowed with burned tips (not from nute burn but from hunger).

Alright! How much do you water to run off and do you collect it somehow? Some minerals binds stronger and accumulate easier than other.

If you let your plants sit in runoff you never really replenish the medium and minerals will always accumulate to some degree, that's why you might see signs of excess N while still feeding less total EC in the end of flower. It's all about keeping the correct mineral ratios and pH in the medium and keep on replenishing it.

Talking about adding this or that is rather pointless IMO with a complete plant food in good to optimal ratios? Then it could only really come down to the growers skill and technique if the environment stays optimal or not in terms of correct pH and EC in the medium and keeping minerals bioavailable.

Cheers!

 

[Gee64]

I follow the logic but, a few things:

- I do supply the calmag with every watering, slowly increasing it from 0.1 to 0.4 within 5-6 weeks. There isn't a one time application that could trigger such an event.

- Also the recommended dosage is is 1ml/L and it give them only 0.1 to 0.4 which should be a safe approach.

- I can recognize cal and mag deficiencies and I rarely see them in less than 5% of the plants, so I bet I give enough calmag, or in the lower levels.

- Also I grow in Lightmix, initialy charged with some food to last for a week and then basically its peat and perlite. So lets root out any advanced live soils, soil amendments ect.

- I also apply properly brewed worm casting teas from week 4 of flowering until the end - roughly 50ppm is the tea after delusion. This includes some additional N and P (I add a little bat guano, that is high in P). Altogether, the tea can't be the issue here, I've skipped teas and it didn't improve or worsen 't anything visibly.

- My water source is considered nearly perfect with about 50ppm some of which is calcium. Also the nutres I use are organic, derived from Alge. It probably also has some calcium in it as manufacturer (Plagron) does not recommend adding any additional calmag.

Not that it is clear that I dont give the calmag at one concentrated dosage, but rather gradually and in small quantities, should I increase it or reduce it all togther if you still believe this is the issue with leaf darkening?


"Your before and after are classic calmag results." this is what I am not convinced of.

If you give them a tea that contains a high dose of nitrogen fixing bacteria that can also cause it.

Usually its calcium though is all.

When your soil dries out is the pot hard and crusty or soft and fluffy? can you easily poke your index finger all the way in ?

Sometimes calcium is the issue but it mimics a nitro deficiency so you add nitrogen but it doesn't work, so you add more but it still doesn't really work. Then you add calmag and all that added nitrogen gets freed.

Excess magnesium in the soil can tie up nitrogen on a 1 to 1 basis. Because calcium and magnesium need to be in ratio to function properly, low calcium is identical to excess magnesium.

So if excess magnesium has a ton of nitrogen locked up and you add calcium, now you no longer have excess magnesium and all that locked up nitrogen gets released at once, literally. On contact.

I am not saying for sure thats what is happening here but it is a common enough organic problem that I carry that picture to help explain it. You gotta admit, our pictures look pretty darn similar.

And if its not the cause at least you got to watch a really informative video.

 

[plan500]

just no. that shit only returns generic junk. grow by it if you wanna live milquetoast.





how much does your nute carry ? what are your using for water ?
you may not need it if you are not on RO. the amounts you are adding don't really mean much.




it's a bit high in N. a lot of nute schedules run that way in veg. they usually build a slight excess in veg to get it all the way through when it hits flower. most schedules pull it back a bit in flower, but the plant will use some all the way through.




that's where your schedule built the N in veg.




you can pull back a little if concerned and run half to 3/4 in veg. otherwise follow the schedule and continue on.

the nute schedule has been built likely based on RO or a low ppm water source. it's impossible to know what the conditions will be like for every grower, so that is how the nute companies set the schedule.

your conditions will not match exactly, there will be some variance, but not a lot. it's up to you to read the plants and adjust as necessary.

****************
"how much does your nute carry ? what are your using for water ?
you may not need it if you are not on RO. the amounts you are adding don't really mean much."
****************

I use general hydroponic CALMAG, that is 200ppm per 1ml/L . So I give them, starting from 20ppm through veg and early flowering, up to 80-100ppm in late flowering weeks 5-9.

Water is 50ppm, from the city tab, close to RO but not that low on minerals.


***************
"it's a bit high in N. a lot of nute schedules run that way in veg. they usually build a slight excess in veg to get it all the way through when it hits flower. most schedules pull it back a bit in flower, but the plant will use some all the way through."
***************
So basically you are saying that plants do look a bit overfed by Nitrogen? This is important to clarify, as this is my original concern, but a few people here and also on another forum express opinion that the darker leaves are the more healthy ones. It confuses me, as for me some of the top leaves have clear nitrogen toxicity symptoms.

 

[plan500]

OK to summarize, so far there have been roughly the following theories behind the sudden leaf darkening:

1. Calcium is causing the unlock of Nitrogen that makes leaves darker. (but i give it in small amounts and gradually)

2. Additional P and K, is unlocking Nitrogen by improving overall processes. (but, the actual result does not look very healthy)

3. The leaf darkening is normal and all healthy plants go through this change in flowering. (beginning to agree, but still think mine have been overfed with N, at least a bit)


My theory related to temps and VPD is still valid and will be tested in the following couple of weeks.

"high temps of 30-31 degrees (84-87F) might cause excessive evaporation and water uptake, that might forcibly make the plants to update excessive amounts of Nitrogen.

 

[Gee64]

OK to summarize, so far there have been roughly the following theories behind the sudden leaf darkening:

1. Calcium is causing the unlock of Nitrogen that makes leaves darker. (but i give it in small amounts and gradually)

2. Additional P and K, is unlocking Nitrogen by improving overall processes. (but, the actual result does not look very healthy)

3. The leaf darkening is normal and all healthy plants go through this change in flowering. (beginning to agree, but still think mine have been overfed with N, at least a bit)


My theory related to temps and VPD is still valid and will be tested in the following couple of weeks.

"high temps of 30-31 degrees (84-87F) might cause excessive evaporation and water uptake, that might forcibly make the plants to update excessive amounts of Nitrogen.

Its really easy to eliminate my theory. Just let your pots dry out until they are quite light but not wilty.

Are they hard to squeeze because they feel lumpy and crusty, and can you easily poke your finger in all the way? If its soft and fluffy its not low calcium.

 

[plan500]

This would be very subjective for me to judge. My pots always dry out to 90-95% before I water and it never felt soft and fluffy after week 4 of flowering from what I recall. But I also haven't paid a lot of attention to the soil so can't tell.

 

[SmokingWings]

Post 25 and 29 plus a video explanation in post 32 that you haven't got the time for.

I amended my earlier msg to say that I was not going to sit here and watch the video but would listen to it. Which I have started to do and have about 20 minutes left.

The man giving the seminar mentions about some of the elements coming from the atmosphere and did mention each time about going through microbes first but it was the briefest of mentions. Total time for the explanation of the the cycle of going from atmosphere to a usable element is about 5 seconds.

It seems that he is attempting to encourage some type of larger view of various organic or natural sources for growing successful crops but is not explaining the hows and whys of the points he is trying to make.

I should be able to finish listening to the video on Monday when I get back from a sudden and unplanned family visit this weekend.