Discoloration on leaves - Doctor needed? : )

[Jingo]

PS: run off of about 10 to 20% every time you water is critical when you're feeding and inert medium you don't want any of your nutrients to build up in your medium over time.

[Jingo]

and now that I think of it, you need to make sure your plants don't reabsorb any of that runoff so they can't be sitting down in trays while you're watering you have to elevate them above your trays or come up with some other system. If you got room you can just put them in the bathtub or something like that.

[marky4marx]

Hi everyone,

There have been some developments and I think the problem is getting worse. They are now in week 4 and as you can see those white patches are still there. The white discoloration seems to be more evident in the bottom leaves. Also I have just noticed that a couple of the bottom leaves have some dark spots (see the first picture).

I gave the first feeding (1/2 recommended amount of fertilizer for growth) about 1 week ago.
I also noticed that the PH of the runoff was too high, (around 7-7.5 (can´t tell exactly as the PH tool I bought is analogue - I´ve ordered a digital one).
Yesterday I watered with PH around 6 to try to rebalance the levels. I gave more water than before, and immediately after watering the leaves drooped. However this morning they are no longer drooping and look find apart from the white patches and those dark spots taht are starting to appear on the bottom leaves.

Is it simply that the PH has been too high? Any suggestions would be very much appreciated.

Thanks!

Mark

[Jingo]

Those bigger white patches just look like some sunburn I never seen that bright white of a color but the pattern is definitely one of something shining on the leaf with another spot being blocked or shaded. Those other leaves are getting chewed on by probably aphids or something, it's hard to say if it becomes an issue insecticide with pyrethrin would be good.

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[marky4marx]

Thanks Jingo, I did see a couple of jumpy insects, but they only just arrived 2 days ago, already been spraying them with some neem oil mixed in a potassium soap solution.

Are you sure the bright patches are sunburn though? Firstly, the lower leaves seem to be the most affected and they get less sun. Secondly they only get about 5.5-6 hours of direct sunlight per day.

[Jingo]

Thanks Jingo, I did see a couple of jumpy insects, but they only just arrived 2 days ago, already been spraying them with some neem oil mixed in a potassium soap solution.

Are you sure the bright patches are sunburn though? Firstly, the lower leaves seem to be the most affected and they get less sun. Secondly they only get about 5.5-6 hours of direct sunlight per day.

No I'm not sure mate, that's kind of an odd pattern. But you're probably watering down lower and if you get a little bit of water on your leaves they'll magnify any kind of light you've got. I've seen sun damage burn right through a leaf before. But I'm really not sure?

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[marky4marx]

Hi again everyone,

It seems that the discoloration might be due to potassium deficiency. I´m now in week 7 of these autos. 5 or so hours of direct sunlight per day, one of the plants started budding quite a bit but the others are only just starting to pre-flower.

Since purchasing a more accurate PH reader I have found that the runoff water is about 7.5PH (probably because I was watering with the local tappwater which has a PH of around 8.2.
I tried to correct this by watering with pH adjusted water of 6, 3 weeks ago. This didnt change the PH of the runoff water much so I watered it with a PH about 3 liters per plant (11L pot) of around 4.5-5.5 about 2 weeks ago.

Then I noticed that the bottom old leaves of the plant were turning yellow/white and gettings some black necrotic spots. Some of the smaller leaves at the bottom of the stem started to shrivel up and die. After research I figured out that this was most likely a Potassium deficiency (exacerbated or possibly caused by my high PH which meant the plant could not absorb the potassium).

The problem is most obvious on the plant which started flowering the earliest and has actually started growing some buds. In fact the other plants have only just started to show signs of preflowering during this 7th week.

Yesterday I put about 3 litres of water in each plant of 5.6 PH to try and bring the PH down even further, and mixed this with a fertilizer which contains more potassium, I used 1/2 of the recommended dose as these are autos and read that it is easy to give them nutrient burn. I had only been using fertilier for the vegetative state with quite low potassium levels, so this could also have contributed to the potassium deficiency.
The runoff water is still around 7.3 in spite of using a very acidic water, and yes I am PHing AFTER adding the nutrients.

I have read in some places not to worry too much about the runoff PH, and that it is more important to provide a consistent PH and that the plants can generally adapt.

1. Do you think I am generally taking the right approach (I.e. Provide very acidic water (5.5) to bring down the PH of the runoff water, and start to add some flowering fertilisers that are high in potassium)?
2. Is watering with PH 5.5 too low (I read potassium uptake is optimal from 6.1-6.9) and going to exacerbate the potassium deficiency as the plant cannot absorb it with the water so acidic? Would it be better to water with a more balanced PH of around 6.5 to ensure the potassium can be absorbed and not worry about trying to bring down the PH of the runoff water from 7.3 down?

The other 3 plants as you can see have not really started flowering properly yet and are not displaying very strong signs of deficiency yet. I´ve included some pictures, would really appreciate any help!

[marky4marx]

The top of the sick plant looks ok, green leaves and starting to flower...