My seedlings need first aid - please help!

[Nerdlicht]

Hello everyone,

I am a complete beginner, and this is my first grow. Unfortunately, my seedlings are already showing signs of deficiency after just a few days. I hope you can help me figure out what the cause might be.

I soaked the seeds in water for 20 hours, then placed them between cotton pads in plastic bags until they sprouted. Then, I placed them in Eazy Plug starter cubes and provided them with 250 ppfd light (measured with the Photone app, which has not been calibrated) in a small propagation box with about 80% humidity. The LED is hanging about 30 cm above the plants. Could this be too low? The temperature fluctuates between 25.5 and 28°C.

The first few days were fine, but for the last two days, one plant looks like it’s drying out. I have kept the starter cube moist the whole time. Another plant seems to be heading in the same direction.

I appreciate any advice you can offer <3

 

[ArtfulCodger]

That's about three times as much light as I give seedlings. I'd move the light higher, dim it, or both. Any time I see edge curl, taco-ing, twisting, or any color other than green, I back off the light.

 

[Nerdlicht]

Okay, I have moved the LED from 30 to 62 cm and reduced it to 150 ppfd (measured with the same phone). Additionally, I have misted the inside of the box with water, so now I have 25.5°C and 90% humidity.

I hope they'll get well soon :)

 

[Nerdlicht]

At this point, I have a question for understanding: The PPFD value decreases when I increase the distance to the LED at the same intensity. For the plants, 200 PPFD at 30 cm distance is not the same as 200 PPFD at 60 cm distance, right?

Or does it make no difference to the plant from which distance it receives 200 PPFD on the leaves?

 

[cannafarmer420]

At this point, I have a question for understanding: The PPFD value decreases when I increase the distance to the LED at the same intensity. For the plants, 200 PPFD at 30 cm distance is not the same as 200 PPFD at 60 cm distance, right?

Or does it make no difference to the plant from which distance it receives 200 PPFD on the leaves?

You misunderstand PPFD, double the height the PPFD would be a lot lower. It's not the power level

 

[Nerdlicht]

You misunderstand PPFD

Yes, I think so too


That's why I'm trying to understand the connections.


If I double the height, the PPFD value decreases by, let's say, 75% (just assuming). If I then increase the LED brightness until I reach the old PPFD value again, does it amount to the same for the plant? Or can I give this way the plant the same amount of photosynthetically active photons with (much more energy consumption) and keep the temperature lower?

Those are my thoughts...

 

[cannafarmer420]

Yes, I think so too


That's why I'm trying to understand the connections.


If I double the height, the PPFD value decreases by, let's say, 75% (just assuming). If I then increase the LED brightness until I reach the old PPFD value again, does it amount to the same for the plant? Or can I give this way the plant the same amount of photosynthetically active photons with (much more energy consumption) and keep the temperature lower?

Those are my thoughts...

Think of light like rain drops, I know it's weird but actually kind of accurate. There is a limit to the amount of rain drops of light a plant can absorb in a day and to answer your question. 200 PPFD with a light at 1 foot or 100 feet is the same amount of rain drops.

To learn about lights check out MIGRO on youtube

 

[ArtfulCodger]

Yes, I think so too


That's why I'm trying to understand the connections.


If I double the height, the PPFD value decreases by, let's say, 75% (just assuming). If I then increase the LED brightness until I reach the old PPFD value again, does it amount to the same for the plant? Or can I give this way the plant the same amount of photosynthetically active photons with (much more energy consumption) and keep the temperature lower?

Those are my thoughts...

There's no difference at the tops. However, there would be a difference lower in the canopy. Moving the light up and increasing its output to match the PAR reading at the lower hanging height would increase the light penetration (and therefore the effective canopy depth).