Lowest PPFD/Lux

[Keffka]

So I’ve got a plant I’ve been struggling with light wise.. it seems to really prefer the low end of veg ppfd.. I’ve tried to hit it with 600 but it started burning so I’ve dropped it to 475 and it seems ok.. what’s the lowest Lux/ppfd you folks have had to use to prevent burning your plants?

 

[Delps8]

The light saturation point for cannabis is stated as being between 800 and 1000µmols and/or a DLI of 65 mols but to support that light level, the other parts of the grow environment need to be optimized. Perhaps there's something that's limiting your plants' response to the higher light level.

How are you measuring light levels?

What strain are you growing?

What type (photo vs auto)?

What's your light schedule?

What's the grow environment - grow type (soil, hydro), light make and manufacturer, etc., etc.

 

[Keffka]

I’m growing a seed off a outdoor harvest last year that consisted of multiple quality strains purchased from a reputable breeder in our area. It was my MILs grow and like most people in the area it wound up being a devastating final weeks outdoors, leading to lots of seeds, so, I can’t be sure of the exact strain (I know, I’m figuring out my limits and deficiencies before spending my own money on genetics)

I do know it is a photo, I run 18/6 currently. My light is a GC ROI E720 1000w full spectrum led true draw of 720 (non sponsored company, the light is easily googled). It was burning my plants being run at 50% and at 24 inches. I’ve since backed it off to 32 and have to take a look today to see if it’s helped. I use the Photone app full spectrum mode checked against a Lux meter for “calibration” (it gives me the general idea) and I am growing in coast of Maine Stonington blend organic soil. I’m well into veg looking to flip to flower once I’ve got the lights understood better.

Something keeps telling me it’s temperature related but I’m not sure how. My room runs 75-82 with 60 rh throughout the day (lights on) and then 68-72 at night, same rh.

 

[Keffka]

So out of all the research I did on my light I never once came across any site, not even the manufacturer recommending these heights and percentages for growth that I just found. If I would’ve seen this, I never would’ve begun struggling with the light the way I have. Hell, on one of the sites it recommended hanging it 15 inches.. this new find seems far more in line with what I’ve seen from this light so far.

I swear this happens all the time. I will scour the internet and everything I own looking for answers and come up empty. The moment I ask for help though, I magically stumble across what I’m looking for smh

of course this doesn’t help solve why my plants aren’t able to take more light, it does however, help alleviate my confusion about hanging height

 

[Delps8]

I’m growing a seed off a outdoor harvest last year that consisted of multiple quality strains purchased from a reputable breeder in our area. It was my MILs grow and like most people in the area it wound up being a devastating final weeks outdoors, leading to lots of seeds, so, I can’t be sure of the exact strain (I know, I’m figuring out my limits and deficiencies before spending my own money on genetics)

I do know it is a photo, I run 18/6 currently. My light is a GC ROI E720 1000w full spectrum led true draw of 720 (non sponsored company, the light is easily googled). It was burning my plants being run at 50% and at 24 inches. I’ve since backed it off to 32 and have to take a look today to see if it’s helped. I use the Photone app full spectrum mode checked against a Lux meter for “calibration” (it gives me the general idea) and I am growing in coast of Maine Stonington blend organic soil. I’m well into veg looking to flip to flower once I’ve got the lights understood better.

Something keeps telling me it’s temperature related but I’m not sure how. My room runs 75-82 with 60 rh throughout the day (lights on) and then 68-72 at night, same rh.

Good info.
Seed is an unknown strain but it is a photo under 18/6
PPFD map below (6" grids)
50% @24" was too much.
50% @32" is OK.
Photone + lux meter.


PPFD map shows ≈ 700µmols across 1' in the middle. At 50%, that's 350± µmols.

 

[Delps8]

So out of all the research I did on my light I never once came across any site, not even the manufacturer recommending these heights and percentages for growth that I just found. If I would’ve seen this, I never would’ve begun struggling with the light the way I have. Hell, on one of the sites it recommended hanging it 15 inches.. this new find seems far more in line with what I’ve seen from this light so far.

Much more uniform at 12", which is unusual. 15" HH? That's definitely near light saturation point (800-1000µmols). Need to have your ducks in a row at that level.

I swear this happens all the time. I will scour the internet and everything I own looking for answers and come up empty. The moment I ask for help though, I magically stumble across what I’m looking for smh

That's how it is in the software world — you hit a problem that you can't work through so you post a message on a forum. As soon as you hit the "Send" button, you figure out the answer.

of course this doesn’t help solve why my plants aren’t able to take more light, it does however, help alleviate my confusion about hanging height

Agreed, but it does feel better to get it off you chest sometimes.

From your other posting:
"Something keeps telling me it’s temperature related but I’m not sure how. My room runs 75-82 with 60 rh throughout the day (lights on) and then 68-72 at night, same rh."

Are you familiar with vapor pressure deficit? If not, skim this info. In short, as do humans, plants prefer certain combinations of temperature and RH. Hot and humid = muggy and it's harder for plants to transpire (throw off water), just like humans. On the other hand of the spectrum, hot and dry = high transpiration = humans sweating = lots of water uptake and "exhaling" which, for plants, means they take up more nutes.

All that to say that your temperature and RH are pretty good for veg so I don't think that's the issue.

This is a screenshot from one of the Bugbee videos. I use it as a "how to" guide.

"wind" = airflow. You should have fans running, one reason being to ensure that CO2 is removed from the tent.

CO2 = ambient or enriched (just to make sure) ?

Next step is below the root zone and soil and soil nutes are beyond my ken. The only thing that I can think of is something really hinky with nutrients or it's that plants' genetic make up.

At this point, we go to level 2 tech support.

How about pictures of the grow and the plant itself?

What type of soil and what nutes?

I was fortunate enough to get excellent help from @Rexer on one of my previous grows. The "@" is the bat signal, so hopefully he will have time to lend a hand.

 

[Keffka]

Awesome write up and response, thank you! I did read about VPD, however I have never seen the cardinals of light that you posted. That, and you mentioning root zones, reminded me, I checked my water yesterday. I believe I have been feeding my plant with 78ish degree water, possibly even 80 and after doing some reading, the root zone doesn’t seem to enjoy that temperature water, could that be it?

CO2 is ambient.. I have 2 fans in the room blowing.. one is aimed in between the lights and the canopy and the second is a small usb fan that blows along the bottom.. I am currently in Coast of main Stonington blend organic soil. I haven’t used any nutes. I did a lot of reading and CoM is supposed to have enough nutrients to run a just add water grow when run in a 15 gallon pot so I figured I could just uppot as the nutrients wore out in the smaller pots. I did pickup the plant food and the fish bone meal it recommended as well as earthworm castings but haven’t used them yet. Coming up this week will be right around her time to take some food if I don’t flip flower, and fish bone meal if I do.

As I typed all of that up, I realized, that it’s probably not designed to give enough nutrients to be blasted at top end efficiency PPFD especially if I’m not running in a 15 gallon.

 

[Keffka]

You can check the grow journal in my signature for the current grow, or, I’m gonna be taking some more OP specific pictures to get an idea of any deficiencies and will post those

 

[Delps8]

I read through the journal and could that be a mag deficiency rather than light bleaching?

Too much light causes issues in the leaves that are closest to the light source. Light intensity falls off very quickly so foliage just a few inches further from the light may not be impacted. Does that pattern describe what you're seeing?

Initial symptoms usually include light avoidance - leaves rotating around their horizontal axis and canoeing or "tacoing" of the leaves. Light bleaching occurs later in the process. You can also end up with light bleaching in the flowers - Bugbee believes that to be a result of high light levels in veg that don't manifest until flower. I thought that was interesting…

Re. pH'ing water before adding to soil - might want to look through this thread.

A diagnosis of a "cal/mag deficiency" seems common. I wouldn't blindly add CM because it can throw off uptake of other nutrients. I had a mag deficiency in my second grow and it was resolved by an Epsom salt foliar spray.

One thing to check - what deficiencies impact the ability to absorb light? That information might prove useful.

 

[Keffka]

I read through the journal and could that be a mag deficiency rather than light bleaching?

Too much light causes issues in the leaves that are closest to the light source. Light intensity falls off very quickly so foliage just a few inches further from the light may not be impacted. Does that pattern describe what you're seeing?

Initial symptoms usually include light avoidance - leaves rotating around their horizontal axis and canoeing or "tacoing" of the leaves. Light bleaching occurs later in the process. You can also end up with light bleaching in the flowers - Bugbee believes that to be a result of high light levels in veg that don't manifest until flower. I thought that was interesting…

Re. pH'ing water before adding to soil - might want to look through this thread.

A diagnosis of a "cal/mag deficiency" seems common. I wouldn't blindly add CM because it can throw off uptake of other nutrients. I had a mag deficiency in my second grow and it was resolved by an Epsom salt foliar spray.

One thing to check - what deficiencies impact the ability to absorb light? That information might prove useful.

Awesome insight! So after hashing it out a bit more I believe the main threat to my light absorption is/was indeed the mag deficiency.. Since magnesium is essential for light absorption I imagine I burned my plants slightly right as the deficiency was showing itself which is what lead to my confusion over diagnosing it. I added the food in today and will keep a close eye on it!

I really appreciate your style of guidance.. Didn’t feed me the information and challenged me to take ownership of the problem. That’s a talent.

 

[Delps8]

Awesome insight! So after hashing it out a bit more I believe the main threat to my light absorption is/was indeed the mag deficiency.. Since magnesium is essential for light absorption I imagine I burned my plants slightly right as the deficiency was showing itself which is what lead to my confusion over diagnosing it. I added the food in today and will keep a close eye on it!

I really appreciate your style of guidance.. Didn’t feed me the information and challenged me to take ownership of the problem. That’s a talent.

You did the work, I just asked the questions.

 

[Rexer]

The bat signal was delayed lol. Sorry I just noticed the missed tag.

First big question- what's the temperature in the grow area? How are you controlling it?

I see now that it's mostly corrected?

I've struggled at the start of each grow almost with light heights. Now I use a cheap lux meter at the start of the grow, and dial it up slowly as the plants age. Takes the guessing out and gives consistent starts to the grows.

 

[Keffka]

The bat signal was delayed lol. Sorry I just noticed the missed tag.

First big question- what's the temperature in the grow area? How are you controlling it?

I see now that it's mostly corrected?

I've struggled at the start of each grow almost with light heights. Now I use a cheap lux meter at the start of the grow, and dial it up slowly as the plants age. Takes the guessing out and gives consistent starts to the grows.

lol that’s alright.. it’s my first indoor grow and my first grow on my own so I already planned for mistakes lol.

The temperature is 75-82 with 55-65 rh.. the plants seem to respond much better to 80ish with 60ish rh.. right now they’re taking 31 DLI.. I’m still waiting to see the yellow tips pull back before I try to get it to take more light.

I’ve learned to ignore hanging heights.. I burn seedlings when they’re less than6 feet away at 50% power. Even at 6 feet and 50% it still gets them a little bit but there’s zero stretching and nice tight node spacing in the females. I haven’t seen a single video or review where someone hung their light 6 feet away lol.


All of my plants keep showing the exact same deficiencies so I’m overlooking something. They look like they’re starting mag deficiencies then start showing light burn soon after. When I was outside I only saw one mag deficiency and that’s because I pushed a plant too far in its starter.

 

[Keffka]

4 seedlings.. 3 are being given ph perfect micro grow bloom so they should be getting the calmag anyway.. even the ones that got their nutes upped and are darker green still have some light coloring on their tips of the new growth

 

[Keffka]

The conclusion that I have come to is that I’m pushing the plants harder than I realize and should be adding more nutrients whether it’s the micro grow bloom or the dry ferts for the female.. I was trying to be as hands off as possible but if I’m trying to grow it at max efficiency I can’t really be hands off.. although I feel the plant should be able to take more than 30 DLI without needing help.. ahh the joys of learning new hobbies lol

 

[Keffka]

Re. pH'ing water before adding to soil - might want to look through this thread.

Phew that was a read lol.. they mentioned explaining the best way to test soil ph but I didn’t see it anywhere.
EDIT: Got my answer.. slurry test or pour through method

 

[Keffka]

@Rexer @Delps8 so I finally got the plant to start raising back up again and have fixed my deficiencies. My question now is.. is there a slight canoeing going on and can you see if it looks like light stress? It’s been a while since my plant was happy so it’s hard to tell if it’s happiness or canoeing from stress

 

[Keffka]

It seems to only be effecting the top of the canopy which makes me believe stress, however that misdiagnosis is what got me here to begin with lol

 

[Rexer]

@Rexer @Delps8 so I finally got the plant to start raising back up again and have fixed my deficiencies. My question now is.. is there a slight canoeing going on and can you see if it looks like light stress? It’s been a while since my plant was happy so it’s hard to tell if it’s happiness or canoeing from stress

There may be a slight canoeing, hard to tell from the photo IMO.
Not enough for you to stress over, she should be ok from what I see in the photo.

 

[Keffka]

There may be a slight canoeing, hard to tell from the photo IMO.
Not enough for you to stress over, she should be ok from what I see in the photo.

So it definitely turned out to be some tacoing/canoeing here’s this mornings images.. can also see real light burn.. learned about a hundred lessons this last week . I backed my plant off a couple inches and will be administering another round of calmag, haven’t decided whether I wanna foliar tonight or wait for it’s watering.. may do both.