Grow lights scorching new sprouts

[ssummer]

Hey all, new to the forum, my name is Sam. I am growling tobacco in a very small batch for the first time. I have some questions regarding germination into actual sprouts. I have seen all over to put grow lights within 1-3 inches of new sprouts. I did this with my grow lights and within a couple hours a scorched a cell tray of some new sprouts… am I doing something wrong here? So two questions
1. How do I get the perfect amount of artificial light on my new sprouts, i have a temperature probe on my seed tray, is there a temperature I should not exceed as a good starting point?
2. at what point do I get light on my new sprouts? As soon as I see some green or a couple days after when they start to develop a stem and some leaves. I also attached some pictures of my sprouts as they are currently(the sprouts that were not scorched.
Thanks again guys. Any help would be appreciated. Also the scorched sprouts were under a led AND fluorescent grow lamps. Next time around I plant to have them under t5 grow lights which I will attach a link to for some reference. The sprouts in pictures
below are under a viper spectra lamp a couple inches above at 25% output(see photo)

https://a.co/d/etxRoWG

https://a.co/d/e0BPD2X

 

[deluxestogie]

Welcome to the forum. Feel free to introduce yourself in the Introduce Yourself forum, linked in the menu bar. You may wish to scan through the topics in our Index of Key Forum Threads, also linked in the menu bar.

I'm a dummy on artificial lighting. Other members may be able to answer your questions on that.

Bob

 

[adamziegler]

How do I get the perfect amount of artificial light on my new sprouts, i have a temperature probe on my seed tray, is there a temperature I should not exceed as a good starting point?

You would use a lab grade light meter. (But you don't need perfect.) Depending on your phone you can use the app "Photone" to get you pretty close to perfect by helping you to measure DLI. I am not sure I would waste my time with cheap light meters from Amazon, but people do. Without a phone that supports it, you can look at the manufacturers spec... Many often include a map that shows PPFD at a specific distance from the light. (You can find online calculators that help you convert PPFD to DLI)

If that all seems overwhelming... Just move that light way further away from your seedlings. Try about 12-16" at your current intensity, and if they start to get leggy move it a few inches closer.

Example, I might use a 30w led (incandescent replacement) that is 6-8" distance for a few veggie seedlings. Your 250w seems way too close. While heat is one factor, you can burn seedlings with too much light.

One final warning... A lot of grow light information out there these days seems to be focused on growing canabis and pushing limits. That info is not always very applicable to growing veggies and tobacco. "Perfect" Light requirements are not the same for all plants, and starting seedlings does not require pushing physical limits.

 

[ProZachJ]

Tobacco does not require extremely high light intensity. With a T5, 8"-12" above the tray should be fine. No closer than they'd be if a tall humidity dome were in place.

I looked at the marketing PPFD map for the viper spectra and based on it I'd suggest 12"-18"

 

[GreenDragon]

Yes, I agree with those above. Raise the lights to 16-18" and monitor. If they get leggy after a few weeks, lower the light a few inches. The old 3" rule was mostly for old style standard fluorescent bulbs from the hardware store - not moder high intensity lights.

 

[revco]

I've been using modern LED's for a decade now. The advice to use a light meter app on your phone is the right way. I generally try to target about 18,000-20,000 lux, at the plant's tips. This is generally safe for very small seedlings. As they grow, I just let them grow into the light as more maturity will also allow for more light.

 

[WillQuantrill]

As mentioned above, I haven't found "perfect" info regarding grow lights for tobacco seedlings so my experience has been trial and error. What I have refined my process to is hanging the lights about 14" about the sprouts and measuring light intensity with one of those 3 in 1 garden testers I turn the intensity of the lights down till the needle starts to move down from 2000 lux to about 8-900 when both lights are at the same output. Reminded me of tuning a dual carburetor intake. As the plants grow up I slowly turn the intensity up. Don't know if this helps much but I have found that my seedling warm mat is really only helpful during germination. I grow in a climate controlled basement so the lights coupled with warming mat just roasts the soil. As far as germination and introducing light, I cover the seeds 2 nights then as soon as I see baby sprouts I hit em with the light programmed on a timer.
Much like all the other aspects of this hobby, what works for some may not work in my application so instructions I interpret as guidelines I can play with. Hope this helps and welcome to the forum.

 

[wruk53]

Here's a low-tech method for you, hold the back of your hand under the light at a distance that starts to fell uncomfortably warm to your skin, then raise the light up a few inches or more than that distance from the top of your plants. I think it's the heat that damages the plants more so than the intensity of the lights.

 

[ssummer]

You would use a lab grade light meter. (But you don't need perfect.) Depending on your phone you can use the app "Photone" to get you pretty close to perfect by helping you to measure DLI. I am not sure I would waste my time with cheap light meters from Amazon, but people do. Without a phone that supports it, you can look at the manufacturers spec... Many often include a map that shows PPFD at a specific distance from the light. (You can find online calculators that help you convert PPFD to DLI)

If that all seems overwhelming... Just move that light way further away from your seedlings. Try about 12-16" at your current intensity, and if they start to get leggy move it a few inches closer.

Example, I might use a 30w led (incandescent replacement) that is 6-8" distance for a few veggie seedlings. Your 250w seems way too close. While heat is one factor, you can burn seedlings with too much light.

One final warning... A lot of grow light information out there these days seems to be focused on growing canabis and pushing limits. That info is not always very applicable to growing veggies and tobacco. "Perfect" Light requirements are not the same for all plants, and starting seedlings does not require pushing physical limits.

Ok so I actually got a par meter, I got both of my grow light set ups in the rough range of 230-270par and 11-14 DLI depending where I put my par meter on the seed trays, is par the same as ppfd? As far as I’m seeing I get some yes and some no? Is 230-270 the correct par for tobacco germination and seedling growth so they don’t get lanky? From my research and from what I’m reading here it has nothing to do with how far away the lights are but how much par or ppfd the lights are putting out to the seeds/plants.
One more thing. I have been seeing many people use the humidity domes to help germination. My only issue with that and the lights in general is it can get very warm under those lights, they can get up to 85-90 in the humidity domes with the lights at the proper distance for me to achieve the 220-270 par. Is there a better way to keep these humidity domes cooler or am I missing something? Also I’m generally wondering how hot the seedlings are allowed to get when these seeds sprout into seedlings and the humidity domes come off.

 

[highgrave]

I have the same light. I think you are running it too close to your seedlings. I have mine at 16", and all I change is the intensity as the seedlings mature. The first two weeks were 50%, then 70% on the 3rd week, and 100% after that. It has worked well for me, and this is my second season using it, with 3 batches of seedling produced so far.

 

[ProZachJ]

Is 230-270 the correct par for tobacco germination and seedling growth so they don’t get lanky

For most seedlings 300 is my default starting point. Tobacco has done great at that level.

 

[adamziegler]

230-270par and 11-14 DLI depending where I put my par meter on the seed trays, is par the same as ppfd? As far as I’m seeing I get some yes and some no? Is 230-270 the correct par for tobacco germination and seedling growth so they don’t get lanky?

PAR has changed definition over time which is why you are getting mixed info. Modern meters are often PPFD... But you should check your device literature and see if the 230 to 270 is mol/m^2/s. If your meter gives you DLI then your numbers correspond well with PPFD / DLI. 11-14 DLI is probably fine for initial germination starting seeds.

Presuming that you were going to grow these outside once you get sprouts, do what you can to start getting them outside soon so that they can harden off and get real sunlight for several days to a week before you put them in the ground.

I am still about 2 weeks out from planting outside. (Late seed starts this winter and weather is strange). My seedlings, tomatoes, peppers, snap dragons, tobacco... Etc are all getting about 25-30 DLI when it's too chilly to be setting trays outside in the sun. I am unsure how "ideal" that range is for all the plants I listed... But generally they look healthy and are showing growth ( except for the snap dragons... They seem like they are getting a bit too much!)

 

[ssummer]

PAR has changed definition over time which is why you are getting mixed info. Modern meters are often PPFD... But you should check your device literature and see if the 230 to 270 is mol/m^2/s. If your meter gives you DLI then your numbers correspond well with PPFD / DLI. 11-14 DLI is probably fine for initial germination starting seeds.

Presuming that you were going to grow these outside once you get sprouts, do what you can to start getting them outside soon so that they can harden off and get real sunlight for several days to a week before you put them in the ground.

I am still about 2 weeks out from planting outside. (Late seed starts this winter and weather is strange). My seedlings, tomatoes, peppers, snap dragons, tobacco... Etc are all getting about 25-30 DLI when it's too chilly to be setting trays outside in the sun. I am unsure how "ideal" that range is for all the plants I listed... But generally they look healthy and are showing growth ( except for the snap dragons... They seem like they are getting a bit too much!)

Gotcha. Any idea on the general temperature for germination? Like I said if I leave the humidity dome on with the proper ppfd/par the temp in the dome gets up to 85-90. As of now I have the domes cracked open with some air flow from a soft fan to help keep it at 80 and below. The only issue with that is it sets out the surface of the soil very fast so I constantly have to mist them. Also do you even worry about temps when the dome comes off after they sprout? At that point I should really just be concerned that they are getting the proper lighting. And what would the proper par/ppfd be when they sprout?

 

[ssummer]

For most seedlings 300 is my default starting point. Tobacco has done great at that level.

Gotcha as stated my only issue with going up that high is I constantly have to have airflow into the humidity domes which cause the soil to dry out. Then I have to keep misting them. Making the humidity dome pretty much pointless. Even without the humidity dome and with a light breeze from a fan my temps are reading around 85 which I see is a bit too high for the seeds. What par/ppfd do you have once the seeds sprout? Trying to get an idea what light intensity people are using at different stages of growth

 

[adamziegler]

the general temperature for germination

60-80F soil temp works for me

 

[adamziegler]

Also do you even worry about temps when the dome comes off after they sprout? At that point I should really just be concerned that they are getting the proper lighting. And what would the proper par/ppfd be when they sprout?

Tobacco grows well in warm environments. 65F+. In seedling trays I don't get up above 85F.

You really should not be concerned about proper lighting unless you are going to grow this completely inside under your light. Get them started and work on moving them outside when it is nice out.

The PPFD levels you discussed already would be good for initial sprouts. I shared with you my current DLI levels for sprouts that are a few weeks past germination.

 

[ssummer]

Tobacco grows well in warm environments. 65F+. In seedling trays I don't get up above 85F.

You really should not be concerned about proper lighting unless you are going to grow this completely inside under your light. Get them started and work on moving them outside when it is nice out.

The PPFD levels you discussed already would be good for initial sprouts. I shared with you my current DLI levels for sprouts that are a few weeks past germination.

So a few days after germination I take off the humidity dome. Put light on it measured at around 250par give or take. And this is what I come home to… any thoughts?? Most of the sprouts are wilted

 

[Knucklehead]

So a few days after germination I take off the humidity dome. Put light on it measured at around 250par give or take. And this is what I come home to… any thoughts?? Most of the sprouts are wilted

Do you have water in the tray? They look awfully dry.

 

[ssummer]

Seedlings are almost a week after germination. From the research I have done I have seen a good par/ppfd of 250 is good at the seedlings stage. So today I did exactly that. Took the humidity dome off almost a week after they sprouted because the seedlings started to become slightly leggy. Dropped my two ballasts with my fluorescent grow lights down to where my meter read approximately 250 par at different areas of the seed tray. I then left for work, I also put a fan in the room for a very light/sutle breeze as I am concerned about the plants getting too hot from the ballasts, I come home after work. My thermometer reads about 83 on the surface of the seed tray, and 70% of my seedlings are wilted, this is my first time growing tobacco or anything for that matter of fact. Any help would be appreciated.

 

[johnny108]

The fan did it- my first seedlings did the same. A light breeze can completely dry them out. Leaving standing water in the tray for the first week+ is also a good idea.
If they don’t recover, you can start again, but leave the fan off for the first few days/weeks.