Too much light, heat? Help!

Hey guys,

I have done quite a bit of searching on here with little luck. I am trying to grow in a small cabinet (~4'x4'x7') with a 400 MH/HPS system.

I get my plants started under CFL and then once they get going, I switch them over to the grow cabinet. It seems every time I do this the plants start yellowing out from the bottom, curl up and die. If you look on my other threads, I show pictures of some of the symptoms starting. I water them every 3rd day and haven't introduced nutes until the plant is well established, probably 3 weeks into the grow.

My question; is 400w too much for such a small grow cabinet? I lined the cabinet with Mylar so the light is pretty intense in there, or could heat be the problem? I have a small fan pulling air out of the cabinet but maybe it isn't enough? I am getting discouraged but really want some advice on how to do it right and with the proper setup! Thanks for your input or advice.

Regards,

4Twentea

How far from the lamp are the plants?

My plants start being like 3 feet from the lamp a couple of days before they get closer. After some days i can have them like 1,5 foot from the 600hps.

You can't have too much light... Just too much heat What you desribe in yur plants is not heat stress but a lack of nutrients... I give my plants nutrients 1 week in and boy does it make a difference in growth. Not for the hell of it, but the fact they need it. Anyone who says no nutes for 2-3 weeks is just playing it safe and not growing to potential. Any pics of the plants? I bet you have a nitrogen def

got a thermometer? also is it soil or hydro? real soil should have nutrients already in the soil but hydro could use light nutes after a week.
and no that light is not too big for a 4x4 closet,if anything its a bit small as long as you control the temps.

Brimi said:

How far from the lamp are the plants?

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Brimi said:

My plants start being like 3 feet from the lamp a couple of days before they get closer. After some days i can have them like 1,5 foot from the 600hps.

Click to expand...

NewbGrower^.^ said:

You can't have too much light... Just too much heat What you desribe in yur plants is not heat stress but a lack of nutrients... I give my plants nutrients 1 week in and boy does it make a difference in growth. Not for the hell of it, but the fact they need it. Anyone who says no nutes for 2-3 weeks is just playing it safe and not growing to potential. Any pics of the plants? I bet you have a nitrogen def

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I set the light ~4.5 feet above the plants during the entire grow. I was thinking it was nute deficiency but wasn't sure, kind of hard to tell. I was using Blue Mountain Organics but I don't think they contain enough N-P-K to support growth, especially under such extreme conditions. My thought was either heat stress or lack of nutes. I am thinking of going with Jack's Classic All Purpose - then switching to the bloom mix for flowering.

do you ph your water? you could be locking out your uptake also

I check the pH of my soil, its usually around 6.5, which is what it should be for proper uptake, right?

Okay - to update and continue discussion in this thread. This week I moved my plant from an outdoor grow to my indoor cabinet that I recently renovated - new ventilation holes, raised the height of the light, painted the entire interior. I transplanted my female into a 5 gallon home depot bucket and put it under my 400W HPS light. After four days of 12/12, I am noticing the leaves are starting to curl upward and turn brown/yellow - same symptoms I was seeing with my first batch of plants. I am noticing leaves all over the plant doing this, but seems to be slightly more concentrated at the top. When I say all over, I mean sporadically, the whole plant isn't yellowing yet, just in spots. She is a large specimen, 4+ feet and is now only 8" or so from the light. The plant otherwise seems to have transplanted well, and is putting out new bud sites, but I am concerned I am going to lose her if I don't figure out why she and all my plants keep turning brown and yellowing out under my light.

Heat isn't an issue here, I have a fan blowing across the light and good ventilation in the cabinet.

Please help or suggest what you guys think it might be!

Anyone have any thoughts or suggestions?

http://www.fastergrowing.com/cannabis/plant_abusebook.php it looks like a nutrient problem.

^^ Thank you. I am not sure it is a nute problem only because I just transplanted her, and have only applied fert once so far.

420ItsDatTime said:

I set the light ~4.5 feet above the plants during the entire grow. I was thinking it was nute deficiency but wasn't sure, kind of hard to tell. I was using Blue Mountain Organics but I don't think they contain enough N-P-K to support growth, especially under such extreme conditions. My thought was either heat stress or lack of nutes. I am thinking of going with Jack's Classic All Purpose - then switching to the bloom mix for flowering.

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At first I was going to point out the obvious. At 54 inches from the canopy you are getting less than 1/50th of the energy to the plant. The light is too far away.

Then I see the pictures. That pull away shot... god... That thing looks like a Japanese maple rather than a Marijuana plant. But the light looks more like 12 inches from the top. Still that plant looks outrageously tall, so it'd make sense that the lower leaves aren't getting enough light and the plant is prioritizing nutrition.

The damaged leaves look like heat damage, but really localized, like they were burnt by touching a bulb. If it is nutritionally based then it's probably an acidic media messing with the uptake of Magnesium mostly, but also Potassium and Phosphorus at the least.

Get yourself a pH tester, ventilation, a thermometer and hygrometer, and do some more research.

A plant should look something more like these:

Snow Crash said:

At first I was going to point out the obvious. At 54 inches from the canopy you are getting less than 1/50th of the energy to the plant. The light is too far away.

Then I see the pictures. That pull away shot... god... That thing looks like a Japanese maple rather than a Marijuana plant. But the light looks more like 12 inches from the top. Still that plant looks outrageously tall, so it'd make sense that the lower leaves aren't getting enough light and the plant is prioritizing nutrition.

The damaged leaves look like heat damage, but really localized, like they were burnt by touching a bulb. If it is nutritionally based then it's probably an acidic media messing with the uptake of Magnesium mostly, but also Potassium and Phosphorus at the least.

Get yourself a pH tester, ventilation, a thermometer and hygrometer, and do some more research.

A plant should look something more like these:
View attachment 1232231

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I know the plant is huge, if you read my earlier post, you would understand that it was an outdoor grow moved indoors to finish off flowering. I can't tell if this is heat or light burn. I keep reading that plants can't really be burned by light, so I don't know? I also did the test with my hand under the lamp and it really doesn't get to a point that is uncomfortable, warm at most. I do test my soil pH regularly, and I add lime from the get go to ensure the pH stays balanced. I do appreciate your detailed response though. I just want to make sure I get it right this time as I have some seedlings starting and want to produce some decent bud.

So I checked on my plant and slowly the symptoms - those that have taken out my other plants too - have been appearing on my girl that I moved inside "the Japanese maple" as someone called it. So after a bit more pondering and recommendation by "abudsmoker", I decided to check the pH of my household tap water. Before this - in my own stupidity, I was only checking the pH of my soil, which had been in the 5.8-6.5 (acceptable) range for growing in soil. Up until yesterday, I could not figure out why my plants were slowly dying. Thanks to "abudsmoker" for suggesting checking the water alone, it all became very clear. My house tap water has a pH of around 4! I was giving my plants healthy doses of this for some time, and could not figure out why - even after adding lime, my soil would creep back to acidic. Duh - check the water! Thought I would share this experience as it made me very excited to realize and finally be able to rectify this problem that has plagued me from the get go. I was locking out my nutrients using household tap water. Live and learn. Case closed.

4Twenty

Um... Dude. Tap water shouldn't have a pH of 4. You need to contact your water company ASAP!!!

^^yeah that^^^
Calibrate the meter. Municipal water supplies trend toward the alkaline. Acidic water corrodes the pipes.
Fred

Snow Crash said:

Um... Dude. Tap water shouldn't have a pH of 4. You need to contact your water company ASAP!!!

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This is more serious than that. What 420ItsDatTime just said don't make any logical sense. Lime brings the ph numbers down. Ashes bring the ph numbers up. As long as you keep your colors in the green your ph is ok. I take my tests out to the daylight because some lighting can give your eyes a false color reading. Or hold the chart and the test in front of something white.

bird mcbride said:

This is more serious than that. What 420ItsDatTime just said don't make any logical sense. Lime brings the ph numbers down. Ashes bring the ph numbers up.

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Lime only brings the ph down if ph is above 7 (unless you're talking about lime fruit). You can't use dolomite lime as a ph-down i think - it more like buffers soil to keep close to 7 right?

Edit: I agree that adding lime to the soil when water is ph4 (which sounds crazy) sounds good. Lime should move it towards 7 - but not if you're watering with acid water like that.
You could probably adjust the water before watering, but some clean rain water would be king.

420ItsDatTime said:

Anyone have any thoughts or suggestions?

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Are you sealing your room off and using only an exhaust fan? You would do better to blow air in and have exhaust ports without fans. Decreasing the atmospheric pressure(creating a vacuum) will cause nitrogen to desipitate faster(fertilizer reaction). Your plants won't get enough air to breath. Use a white background for reflection.