Possible Magnesium Deficiency?

[purpleskunk777]

My 2-3 month old clones are experiencing yellowing of new growth. The yellowing is localized on the perimeter of the leaf, leaving an arrowhead-shaped darker, healthier green in the center of the leaf. Researching google, I diagnosed this as a magnesium deficiency (whether I was right or wrong) and followed the directions posted under the sticky "epsom salts = not miracle cure)," spraying the leaves (yesterday and today). The condition seems to have become worse since applying epsom salts. My guess is that when I flushed my plants a week ago, I leeched out one or more micronutrients, just can't figure out which one(s). In addition, the newest growth is very light greenish/yellowish and looks "blotted." I will post pictures later tonight, just wanted to get this up ASAP...any ideas??

Here are the specifics:

Grow Medium = Scotts Topsoil (contains peat) + Vermiculite (80%/20%)
Location = Indoors
Nutrients = Miracle Grow All Purpose (1/8 tsp/gal)  (this is ¼ recommended dose)
Rate of application = Water â?? Feed â?? Feed (then repeat). Plant was flushed with water quantity equivalent to pot size once a week ago
Runoff pH = 6.2
Water source = Tap Water is pHâ??d from alkaline to 6.5
Age of plant = 2-3 months
Lighting source and distance from plant = T5/55W/10,000 Lum/6400K/ Within 6â?� above canopy.
Air temperature = Daytime 80 deg. Nighttime 75 deg.
Air % Relative humidity = roughly 50%
Lighting schedule = 18/6
Type of ventilation = 4â?� inline fan (170 cfm) + 12â?� regular (circulatory) room fan
Did NOT pre-soak media in pH corrected solution

purpleskunk777 Reviewed by purpleskunk777 on 09-11-2010. Possible Magnesium Deficiency? My 2-3 month old clones are experiencing yellowing of new growth. The yellowing is localized on the perimeter of the leaf, leaving an arrowhead-shaped darker, healthier green in the center of the leaf. Researching google, I diagnosed this as a magnesium deficiency (whether I was right or wrong) and followed the directions posted under the sticky "epsom salts = not miracle cure)," spraying the leaves (yesterday and today). The condition seems to have become worse since applying epsom salts. My Rating: 5

[headshake]

waiting to see pictures.

-shake

[purpleskunk777]

Camera broke but i bought a new one..should be here in 3 days. I'll post the pics ASAP!!

[WashougalWonder]

There should be enough Mg in tap water to not have a deficiency. Conversely, if you use reverse osmosis, you should add some Cal/Mg.

You might also be root bound and need repotting.

[purpleskunk777]

I use tap water, perhaps there isn't enough Mg in it? Also, I re-potted from 1 gal to 3 gal only 1 week ago, still think it could be root-bound?

[Rusty Trichome]

Topsoil is usually buffered to a lower ph, (6.0 or so) so I'd contact Scotts, and see what their Topsoil is buffered to.

Miracle Grow All Purpose directions are for a 10 to 14 day period. (1 tsp per gallon) Half strength (a weekly dose) would be approx 1/2 tsp per gallon. When I use it, I use 1/4 tsp per gallon, twice a week.

6.5 ph ingoing is a tad low before adding nutrients. Try bumping it up to 6.8 or 6.9ish before nutes. 6.5 ph is fine for plain waterings, though.

Too young for a true calcium or magnesium def. But unsulfured molasses at 1/4 tsp per gallon, once a week usually doesn't hurt, but is mostly unnecessary. In mid to late flower, I give 1 tsp per gallon, once a week.

[purpleskunk777]

Rusty, I called Scotts and they could only tell me that the soil is pH'd to a range of 5.5-7.5. I'll pH-UP my nutrient solution slightly and use Miracle Grow as you suggested.

I should add that the problem has progressed throughout the entire plant (all nodes). New growth is lighter green. I'm going to continue using the Epsom/dish soap foliar spray daily on affected leaves. Liquid Karma is arriving tomorrow; I'm going to see if that will help too.

Shake, I promise to get those pics up ASAP. Do you have any suggestions in the meantime?

All of your help is appreciated, thank you!
-purp

[headshake]

Shake, I promise to get those pics up ASAP. Do you have any suggestions in the meantime?

All of your help is appreciated, thank you!
-purp

i'd like to reserve my opinion before adding anything. apparently i don't know what the fuck i'm talking about. lol.

it sounds like magnesium from the description. again, just my opinion until we get pics/more info.


-shake

[purpleskunk777]

apparently i don't know what the fuck i'm talking about. lol.

Oh, please. Who would say such a thing


I think I found the problem
So I did a runoff once again. ph = 7 going in, 6 out the other end...judging from the chart posted in the sticky of the plant problems forum, P, Ca, and Mg would all be locked out at this pH (less than 6). I flushed with over 3X pot size (12 gal) to a runoff of about 6.7 we'll see how things go I'll keep y'all posted!

[Rusty Trichome]

From what I understand, that buffering range is refering to the wide range of products, not their ph range for the Topsoil itself. Indoor mixes are usually buffered to an approximately neutral ph, (7.0ish) outdoor products (compost, mulch, topsoils) are buffered to a lower ph.

If your ingoing water is 7.0 ph, and your runoff really is 6.0 ph, then the Topsoil is likely buffered to 6.0ish ph. Flushing won't improve this, so I'm curious what you're using to determine your runoff ph? A color-coded test kit assumes you are using clear water. Any tinting of the water will skew the results.

You might want to look for an indoor mix that's properly buffered. Or, you can get some garden lime, limestone dust, or dolomitic limestone to buffer the Topsoil, and transplant asap. Practice on an empty pot of the topsoil, as different buffers need to be applied at different rates, and must be watered-in to prevent root burn. Topsoil is usually heavy in manure, which temnds to burn cannabis roots at those quantities. You need a ph pen for this process, though.

Did you check to see if you're rootbound like WW mentioned?