light burn or something else?

[username92635]

Soil Grow

Strain - Kush, Northern Berry, Northern Skunk
# of Plants - 50
Grow Type - Soil
Grow Stage - Seedling
Setup - ?
Light - 4 fluorescents fixture is approx. 5ft by 1.5ft
Nutrients - none given yet
Medium - soil - ProMix organic seed starting mix
Water is reverse osmosis - ph 6.4
Room Temperature 22 degrees
Room Square Footage - still in nursery container, room is approx. 15-10ft
Pests - None Known
Watering when top soil is light and dry and soil just starts to pull away from container, then I give them a good soak till water runs through. No more often than every 4 days.

Problem: Seedlings are 3 weeks old, doing great till I tried putting them under a 400 watt metal halide, approx. 25' away, let them spend 2 hours under it one day, 16 hours the following day and noticed the first set of true leaves on one plant were curled and turned black on edges and crunchy dry, thought they were dry and watered well that evening, they slept and the following morning I checked on them and noticed a bit of yellow of a separate plant, moved them back under fluorescents. Now more leaves are getting dark spots (usually on first or second set of true leaves) and im freaking out. They are looking worse by the hour! I have never fed them, so I don't believe its nutrient burn and they arnt quite ready for transplant, so not root lock. Please any advice very very appreciated!!!

 

[paul keating]

Hmmm.

I'm not experienced enough to give an accurate diagnoses, but in my opinion, it isn't light burn.
If it was light burn, the top leaves would be burnt, not the lower leaves.
I'd say it was a deficiency. Considering their size, and the fact you have never fed them, it may be time to start.
Looks like a combination of nitrogen deficiency and phosphorus deficiency to me.

Either that, or it could be due to the infrequent waterings. If you let the soil dry out too much, and it pulls away from the side of the pot, that can cause troubles like this too, from what I've read.

Can someone more experienced confirm / refute this for me?

 

[MedScientist]

When you increased the lighting, you increased their need for food, so they started to pull what they needed from the fan leaves. I would start them at 1/4 strength nutes and step Up with each feeding and transplant them soon. Ph looks to be good. They should recover Quickly with some food! Great Job!

 

[username92635]

I haven't bought any nutrients yet, this is my first grow and I thought I wouldn't have to feed them until after transplant (I thought I had a week more). If I transplant them tomorrow in ProMix HP in 3 gallon pots would that buy me a week till I can get to a hydroponic store? Or a recommendation for a nutrient I can find at a hardware store? I really appreciate both replies! Thank you!!

 

[paul keating]

When you increased the lighting, you increased their need for food, so they started to pull what they needed from the fan leaves. I would start them at 1/4 strength nutes and step Up with each feeding and transplant them soon. Ph looks to be good. They should recover Quickly with some food! Great Job!

Thanks Medscienctist.



That was exactly my thinking. When the MH went on, it needed more nutes.
But I'm still learning myself, and there are so many different things that can go wrong, and many of them show similar symptoms.
It's all so confusing sometimes. It's great having such an experienced group of people on here.
I've never asked for help myself, i just try and wing-it. Make it up as i go along.

username92635.
There's lots of great info on this site.
Take a look at this link.
Has lots of useful info in it.

How to Grow Marijuana Everything You Need to Know

 

[username92635]

Thank you Paul, I found that link just after posting this thread and haven't stopped reading. I wish I had found this site a couple weeks ago, its a wealth of information!

 

[paul keating]

I haven't bought any nutrients yet, this is my first grow and I thought I wouldn't have to feed them until after transplant (I thought I had a week more). If I transplant them tomorrow in ProMix HP in 3 gallon pots would that buy me a week till I can get to a hydroponic store? Or a recommendation for a nutrient I can find at a hardware store? I really appreciate both replies! Thank you!!

I'm not familiar with promix HP, but i just did a quick search, and it doesn't look like it has any NPK in it.
You want a fertilizer with some N-P-K in it.
That is Nitrogen-phosphorus-potassium.
Do supermarkets in your country sell any gardening stuff?

Just a basic plant fertilizer would be enough to get by for now.

You can get some fancy stuff later on if you want.

At this stage, you want something high in nitrogen.

Usually the NPK rating will look something like this;
10-5-10.
You want something that says something like that.
You want something with a higher first number of the three.

 

[username92635]

I can get into a hardware store tomorrow that has a small nursery section, I will look for that combination but I'm sure I will only have a few choices to choose from. I am taking a trip into a bigger city center with a good hydroponic store in a week though and will get something more specific. Thanks again for your advice, I'm looking forward to learning all about this new hobby of mine!

 

[businessman]

not light burn. Looks to be related to nutes, lack of