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InvisibleAmnesiac


Registered: 10/13/08
Posts: 102
Loc: Under the sea
Potassium deficiency ?
    #500194 - 11/22/10 11:12 PM (6 years, 18 days ago)

1. Are you growing from seed or clones?
Seed

2. How old are your plants?
2 months

3. How tall are your plants?
less than 1 foot, trained to a screen

4. What size containers are they planted in?
4 gallon

5. What is your soil mix?
50% perlite, 40% peat moss, 10% vermiculite.

6. How often do you water and what type of water do you use?
Well water  every 3-4 days

7. What is the pH of your water?
5.8-6.2

8. What kind of fertilizer do you use and what is its NPK ratio?
I use GH flora series with liquid koolbloom and snow storm ultra. I feed at a rate of with 6 ml floramicro, 10 ml florabloom, 3 ml floragrow, 3 ml koolbloom, 2 ml snow storm ultra, and 1.5 ml pH up per gallon.

9. Do you foliar feed or spray your plants with anything?
No

10. What kind of lights do you use and how many watts combined? (HPS, MH, fluorescent, halogen, incandescent "plant lights")
600w hps and 175w mh

11. How close are your lights to the plants?
The hps is about 12-18 inches and the mh is roughly 16 inches from one side of the screen.

12. What size is your grow space in square feet?
6'Lx4'Wx6'H  24 square feet, 144 cubic feet

13. What is the temperature and humidity in your grow space?
Humidity ranges from 40%-75% and the temp ranges from 62-72 degrees Fahrenheit.

14. What is the pH of the soil?
Good question

15. Have you noticed any insect activity in your grow space?
A few fungus gnats

16. How much experience do you have growing?
3rd grow, 2nd indoor.


Here are some photos

The plants overall are showing signs nitrogen deficiency, but what concerns me is the bleached leaves. It looks to me like a potassium deficiency but, almost all the fertilizers I use have potassium. This leads me to believe that the K is being locked out because excessive calcium or the cooler temperatures.


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InvisibleHawksresurrection
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Registered: 12/05/08
Posts: 13,294
Trusted Cultivator
Re: Potassium deficiency ? [Re: Amnesiac]
    #500428 - 11/23/10 10:40 PM (6 years, 17 days ago)

Well since you ahve no idea what your pH is and peat is pretty acidic that's probably your problem.  That fact that your just throwing in some arbitrary number of mls into your water is insane dude. 

Go get a electronic pH meter, or at the VERY bare bones minimum one of the vial ones. 

Once you obtain this water your plants knowing what pH it is.  Then collect some of the run off and see what that is.  Once you obtain these two numbers you will be able to see about where the pH of the soil, or lack there of, is generally around.  And then once you have these numbers you will have to decide how you are going to go about changing the pH of your soilless soil.


*Edit*

Now this is just to get a VERY general idea of where your pH is.  I'm not saying it is an extremely accurate way of getting.  But the best I've found so far.  All the probes and water tests I've tried suck.


--------------------
Dude she isn't as young as she use to be.

-niteowl


Edited by Hawksresurrection (11/23/10 10:45 PM)


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Invisiblemaryanne3087
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Registered: 06/27/10
Posts: 1,111
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Re: Potassium deficiency ? [Re: Amnesiac]
    #500445 - 11/23/10 11:36 PM (6 years, 17 days ago)

Next time you could try to mix in some dolomite lime and epson salts to buffer the pH. Epsom salts are pH 6.5 and dolomite lime pH 7. So each are useful to raise pH but not exceed a useful pH so they're hard to over apply. I'd probably use each sparingly but some sure would sound beneficial to your situation.

I'd also raise the feed water pH to 6.4 or 6.5 and see if there's improvement. I don't fully understand if peat mediums should be treated like hydroponic as they're not inert at all and are not only decaying but continue to decay rather quickly making their pH unpredictable which is part of the reason I switched to coco. Proper pH for soil is 6.5 I usually fed my ProMix(mostly peat based) potted plants with a pH of 6.1 or 6.2 when I started and found better results at 6.4 or so, your results may vary.

Early K deficiency and Mg deficiencies are hard to tell apart. From the pH I could only assume Mg deficiency is far more likely as Mg becomes less available at pH's lower than 5.8 K is available basically at any reasonable pH. Basically if your K deficiency is pH related, guess what you have a Mg deficiency too.


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InvisibleAmnesiac


Registered: 10/13/08
Posts: 102
Loc: Under the sea
Re: Potassium deficiency ? [Re: Hawksresurrection]
    #500475 - 11/24/10 01:38 AM (6 years, 17 days ago)

Thank you for your responses!

I've got pH drops and check the pH of the nutrients before they go in but, I've never checked the pH coming out. Next time I water I will check the pH of the runoff.

Quote:

maryanne3087 said:
Early K deficiency and Mg deficiencies are hard to tell apart. From the pH I could only assume Mg deficiency is far more likely as Mg becomes less available at pH's lower than 5.8 K is available basically at any reasonable pH. Basically if your K deficiency is pH related, guess what you have a Mg deficiency too.




I have had problems with Mg deficiency early and I fixed it with epsom salt but, when I started flowering and increased the amount of florabloom I thought it would have enough Mg. I've also been watering with a pH of closer to 5.8 for the whole grow so the natural acidic nature of the peat may be coming in to play. Do you know at what temperature K becomes less available? Every thing was going on track until the highs started ranging from 67F-71F.

I guess the next step for me is to measure the pH of the runoff and increase the pH of my nutrient solution to 6.4. Thanks for the expertise and I'll update in a day or two when I water.


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Invisiblemaryanne3087
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Registered: 06/27/10
Posts: 1,111
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Re: Potassium deficiency ? [Re: Amnesiac]
    #500480 - 11/24/10 02:18 AM (6 years, 17 days ago)

5.8 is definitely too low for peat IMO. Most people who grow smoothly with peat / ProMix use a pH of 6.1 or 6.2 for Peat but IMO a little higher is better esp when having problems with Mg def. I'm still willing to bet you have a Mg def and not a K def, if your pH is too low (which it is) and is causing K def you would also be having problems with Mg, but you would have problems with Mg first.

Keep in mind, I use a higher pH for my nutrient solution and also used ProMix which is buffered with dolomite lime/epsom salts I would also NEVER consider using a pH of 5.8 so I'm 100%+ convinced that it's a pH related issue causing Mg def which is easy enough to mistake for K def.

I've also never heard of temperature effecting nutrient availability, and my temps are usually around that 72 or so.


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InvisibleAmnesiac


Registered: 10/13/08
Posts: 102
Loc: Under the sea
Re: Potassium deficiency ? [Re: maryanne3087]
    #500527 - 11/24/10 11:34 AM (6 years, 17 days ago)

That's good to know that it's something I can fix. I'll try to get the pH to closer to 6.6-6.8 until the runoff comes out around 6.2 then drop back to 6.4. I'll also add some epsom salt until I get the pH where it should be.

I was reading this thread (the plant problem solver) and it said cold weather could possibly lock up K but, I think it would have to be a lot colder than the temps I'm running.

I'll be watering tonight when the lights turn on, then collect some runoff to see what the pH is and update. Thanks for the help.


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Invisiblemaryanne3087
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Registered: 06/27/10
Posts: 1,111
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Re: Potassium deficiency ? [Re: Amnesiac]
    #500563 - 11/24/10 02:08 PM (6 years, 16 days ago)

It wouldn't be a bad idea to feed with a high pH nutrient solution if your medium has become highly acidic. I think it's a safe assumption this has occured but you know what they say about assumptions. Either way 6.8 is more than safe, to correct highly acidified mediums within a reasonable time frame you'd be looking at a pH of 8.5 or something like that.


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InvisibleAmnesiac


Registered: 10/13/08
Posts: 102
Loc: Under the sea
Re: Potassium deficiency ? [Re: maryanne3087]
    #500872 - 11/25/10 11:16 PM (6 years, 15 days ago)

The pH of the run off was around 5.4-5.6 and the pH going in was around 6.2-6.4. Next several waterings the pH of the nutrient solution will be between 6.8 and 7.0 until the pH of the runoff is around 6.2-6.4, then I'll drop back to 6.4 pH.


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Invisiblemaryanne3087
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Registered: 06/27/10
Posts: 1,111
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Re: Potassium deficiency ? [Re: Amnesiac]
    #500923 - 11/26/10 04:37 AM (6 years, 15 days ago)

Surprisingly that pH isn't very low for peat it may not be low at all. I'm actually really surprised it's not lower since you have no pH buffers the peat.


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