Is this light burn?

I've got some seedlings, 3x Northern Lights under 110W CFL + some 20W CFL bulbs, hanging 25 cm (+- 11 inches) above the plants.


The EC seems fine, runoff is lower than 1.0 mS/cm when I give 1.0 mS/cm water, runoff pH is 6,5 and I give rain water with a pH of about 6,2. Temperatures stay between 18 and 22 degrees celsius, occasionally to 24 on warmer days. The humidity hasn't gone lower than 50 or higher than 65. I've got a fan blowing on the seedlings through the mesh of my growtent. I'm growing in a mix of peat, coco choir, perlite and garden soil, amended with a little bit of organic nutriënt.

All these conditions seem to be okay, so I can't really figure out why growth has stopped for over a week. The only thing I can think of is light stress. The ridged leaves make me think it's heat stress but it clearly isn't that hot.. I've already removed the bulb which was closest to the seedlings but to no avail. Maybe I should get another thermometer? or should I move up the lights? I figured 25 cm is more than enough for a CFL, considering how much seedlings tend to stretch under them.. They've recently developed some more symptoms; these spots and deformations.




TL;DR: I'm thinking lightstress but I'm not sure if that's possible with my CFLs, can anyone confirm/deny?

Thank you for your time

Hello! It could be due to one or all of them= PH is too high or low, soil too hot with ferts, splashed with feed and left to dry under light...
Sad to say but you better start again, or waste your time. Seedlings stage crucial...
Good luck!

Overwatered and overfertilized.

Nadia786 said:

Hello! It could be due to one or all of them= PH is too high or low, soil too hot with ferts, splashed with feed and left to dry under light...
Sad to say but you better start again, or waste your time. Seedlings stage crucial...
Good luck!

Click to expand...

Yeah I already figured i should probably start over, but I measered pH and runoff EC to be within limits. My soil was indeed too hot, because I stupidly fertilized to soil a few months ago and then left it to mineralize... the result was my runoff EC was 3.0+, However, I flushed the soil until it had a proper runoff EC before even attempting to sow the seeds. It still has a proper runoff EC, so unless my measuring devices are completely off I'd think pH or EC aren't the issue.

MichiganMedGrower said:

Overwatered and overfertilized.

Click to expand...

The runoff EC is between the limits of 0.8-1.3 mS/cm for seedlings, which I gathered from some internet research. If you consider this too high could you advice me another runoff EC value to aim for? Thanks for your input so far

At first use light soil for seedlings and do not over water or mist them under too close light...
Also sometime seeds turns out to be runts! Nothing you can do!

xirb22 said:

The runoff EC is between the limits of 0.8-1.3 mS/cm for seedlings, which I gathered from some internet research. If you consider this too high could you advice me another runoff EC value to aim for? Thanks for your input so far

Click to expand...

The seedlings don’t need any added nutrients for 2 weeks. After that .8 - 1-0 is usually fine to start but potting soil can hold nutes that don’t show in runoff and old soil can be out of balance.

I think it’s the added nutes and it is difficult not to overwater seedlings in large pots. I use a 16oz plastic cup for the first 2 weeks. Then transplant up when the root ball is developed some.

Think how tiny the seedlings little few roots are. They need little water and no fertilizer in the beginning.

I use ocean forest and don’t add nutes in veg at all. I water the proper size pot to runoff and wait for the pot to get very dry and light before watering again. This promotes the roots to search and fill the entire pot looking for water and nutrients.

I suggest you read a Grow book like Jorje Cervantes or Ed Rosenthal or the like to learn about soil and nutes and how the plant grows before trying to learn quickly on the Internet.

MichiganMedGrower said:

The seedlings don’t need any added nutrients for 2 weeks. After that .8 - 1-0 is usually fine to start but potting soil can hold nutes that don’t show in runoff and old soil can be out of balance.

I think it’s the added nutes and it is difficult not to overwater seedlings in large pots. I use a 16oz plastic cup for the first 2 weeks. Then transplant up when the root ball is developed some.

Think how tiny the seedlings little few roots are. They need little water and no fertilizer in the beginning.

I use ocean forest and don’t add nutes in veg at all. I water the proper size pot to runoff and wait for the pot to get very dry and light before watering again. This promotes the roots to search and fill the entire pot looking for water and nutrients.

I suggest you read a Grow book like Jorje Cervantes or Ed Rosenthal or the like to learn about soil and nutes and how the plant grows before trying to learn quickly on the Internet.

Click to expand...

I've transplanted the seedlings in smaller pots with reflushed soil, hoping it will dry out fast and recover the plants. I own a copy of a Jorge's Grow Bible but totally forgot I had it since I lend it to a friend... I really ought to get that back... Thanks for the help!

xirb22 said:

I've transplanted the seedlings in smaller pots with reflushed soil, hoping it will dry out fast and recover the plants. I own a copy of a Jorge's Grow Bible but totally forgot I had it since I lend it to a friend... I really ought to get that back... Thanks for the help!

Click to expand...

If you can't get the book back, borrow $20 from the guy that has it and buy a new book lol.

It’s in here. And many others. I like ed Rosenthal for tech and Clark Marijuana Botany is excellent but highly technical.


http://catnews.org/FREE Pot Books/

MichiganMedGrower said:

It’s in here. And many others. I like ed Rosenthal for tech and Clark Marijuana Botany is excellent but highly technical.


http://catnews.org/FREE Pot Books/

Click to expand...

Holy shit this is heaven! Thanks a lot man! And don't worry, I like the technical stuff

xirb22 said:

I've got some seedlings, 3x Northern Lights under 110W CFL + some 20W CFL bulbs, hanging 25 cm (+- 11 inches) above the plants.
View attachment 4058770

The EC seems fine, runoff is lower than 1.0 mS/cm when I give 1.0 mS/cm water, runoff pH is 6,5 and I give rain water with a pH of about 6,2. Temperatures stay between 18 and 22 degrees celsius, occasionally to 24 on warmer days. The humidity hasn't gone lower than 50 or higher than 65. I've got a fan blowing on the seedlings through the mesh of my growtent. I'm growing in a mix of peat, coco choir, perlite and garden soil, amended with a little bit of organic nutriënt.

All these conditions seem to be okay, so I can't really figure out why growth has stopped for over a week. The only thing I can think of is light stress. The ridged leaves make me think it's heat stress but it clearly isn't that hot.. I've already removed the bulb which was closest to the seedlings but to no avail. Maybe I should get another thermometer? or should I move up the lights? I figured 25 cm is more than enough for a CFL, considering how much seedlings tend to stretch under them.. They've recently developed some more symptoms; these spots and deformations.

TL;DR: I'm thinking lightstress but I'm not sure if that's possible with my CFLs, can anyone confirm/deny?

Thank you for your time

Click to expand...

Not light stress as CFLs should be about 2" away from little plants like that.

If anything is hot it's your soil but unless you've added too much nutrient the mix you state shouldn't be hot.

The spots on your leaves look like low P if anything or burns from water on the leaves but that damage is usually a tan colour so maybe you splashed nute water on them?

Growth has likely stopped because they aren't getting enough light so move them in closer and see what happens. More light comes off the sides of those bulbs than the ends and some tinfoil reflectors on the backs of the bulbs will get you lots more light off them. I've seen pop or bear cans made into small reflectors but I just cut tin foil with tabs at each end to wrap around the base and tuck in at the front so the fan doesn't blow them off the bulbs.

It's not over until they are lying on their sides and shriveling up so don't give up yet!

Good luck!

You shouln't be getting run off with a seedling that small in that big of a pot or soaking the whole medium completely. It's a lot easier to water a seeding in something 'solo cup' size, where you can go ahead and soak the whole pot without keeping the soil over saturated for too long, leading to lack of oxygen, root rot.. The brown/discolored pearlite shows it been damp along time.