Heat Stress or Something Else?

[Ataraxia]

I have some "rusty" colored leaf tips on two of my plants. This only effects a few leaves, mainly towards the top. Some leaf margins are also slightly yellow or golden colored, but the other leaves and plants as a whole are green and very healthy looking. The leaf tips that are discolored are also brittle, and crunch if pinched between fingers. I looked into the trouble shooter, and I thought it may be #6

6) a) Tips of leaves are yellow, brown, or dead. Plant otherwise looks healthy & green. Stems may be soft >> Over-fertilization (especially N), over-watering, damaged roots, or
insufficient soil aeration (use more sand or perlite. Occasionally due to not enough N, P, or K.


I also thought it may be heat stress since it mainly effected the upper leaves. I moved my 250W HPS to 20" above the tallest plant. The plants effected are in FoxFarm Ocean Forest mixed with perlite, peat, and a bit of dolomite lime. One is 20 days old and one is 12 days old. The both started to show this coloration at the same time. I've been watering them with pH 6.75 water and the larger one just got 1/4 strength nutes for the first time. I water every 3 days about, whenever the pots feel light and the top few inches of soil is dry.


pics1 & 2 the 20 day old plant, damaged leaf tips
Pic3: Discolored leaf on the 12 day old plant
Pic4: 20 day old plant, full view
Pic5: 12 day old plant, can see discoloration in top left section of picture

I first noticed this a few days ago, and it hasn't gotten a lot worse since then, but it looks to be beginning to slowly effect other leaves on the plants

 

[DeVeill]

I have the same problem on one of my plant as well. It's probably from heat stress. I have been told not to worry about them and just let them grow. Try to adjust the PH around 6.4~6.5

Goodluck

 

[maineharvest]

Whats the temp of your growroom? I keep a little thermometer close to the tops of my plants so that way I am able to keep the right temp. Do you have a fan on the plants? My closet got up to 95 degrees for a while and my plants burned and completly stopped growing. Once I fixed the temps it took another week for them to start growing again. Right now I have a 400w hps about 14 inches from my plants and they dont burn but ive got a big fan on them. Im going to try to put a link on here for you but im not sure if it will work but it is very helpful to me. Hope it helps you.

http://www.marijuanapassion.com/forum/showthread.php?t=12500

 

[maineharvest]

Good the link worked. I forgot to tell you that they look great other than your one little problem. What strain are they?

 

[Ataraxia]

Thanks for stoppin by. The strain is K2. I pondered this problem while gazing over my girls last night. I held my hand over them and it didn't even get warm. My grow cab is a pretty constant 86* at plant level. I have a 12" oscilating fan blowing just above the plant tops. It gives good air circulation and toughens up those stems. I hope I can just let them "do their thing" and not worry about it, but will it get better or go away? After doing the back of the hand test, I'm fairly convinced that it's not heat stress. Any other possible causes to this problem? My 250HPS is 20" above them, not sure if I said that yet or not

 

[Dankerz]

ok what im going to say is or my question is? when you water with ferts does any of the water get on the leaves cause ive seen this happen to me when to much ferts got on the leaves?? or could just be fert burn to strong of ferts!?

 

[bombbudpuffa]

It's either overwatering or ph related imo.

 

[Ataraxia]

I water only when the feel dry which right now is every 3 days. I've never spilled any water on the leaves. I'm always very careful when watering them, and I've only given ferts one time to the oldest plant. That was 1/2 of the seedling dosage on the label. I'm now pH testing my water, so if that's the problem, then it'll soon clear up. What's the ideal pH to water Marijuana plants with? I've heard several conflicting numbers. I thought it was around 6.2-6.6, can anybody give me a for sure number?

 

[Mutt]

You seem to have it locked on with your schedule....but what is your fert. schedule.
I looked at it.
if overwatering is not the problem, then I thought possibly hard water....but you had lime in your soil that would prtoect against that.
Then realized. 20 days old and only at 1/4 strength...what ferts are you using? I would like to know prior to recommending going up to 1/2 strength.

 

[Ataraxia]

Pure Blend Pro Grow 3-1.5-4 is the organic fertilizer I'm using. Like I said I've only used it once and only on the oldest plant, 21 days old, but I thought maybe I'd use it on the younger one which is almost the same size but only about 2 weeks old. The directions say to use 7mL per gallon for seedlings and rooted cuttings. I measured about 4mL and mixed it into a gallon of distilled water. I wanted to use this lighter dose the first time to be sure I didn't burn them. Two days later, no sign of burn whatsoever. Can I start fertilizing the 2 week old plant? What dosage would you suggest? Also, the directions say "for best results use every watering." Is that recommended? Thanks

the recommended dosage for mid-sized vegetative plants is 15mL and mature vegetative plants is 30mL per gallon of water.