Light/heat damage or toxicity? D33 soil + LED

[SecretFarmer]

Problem: Bleaching/burning tips, clawing tips at top of plant

Medium/grow method: Biobizz Lite-Mix + ~30% perlite in an 11L airpot

Feed: and supplements used: Biotabs starter pack. Bactrex and Startrex in soil pre-germ, 1.5x biotabs inserted on D17, 1x Orgatrex feed.

water source: Tap water, sat out for 24 - 48 hours, pH 8.5 naturally, use Biobizz Ph- to 6.5 - 6.8ish before applying to plant. Following wet/dry cycle for watering.

Strain/age: Sweet Seeds +Speed Auto, D33 from sprout

light used: Invisible Sun LED ISH100, dimmed and running 24/0

Climate: 20 - 24, 45-55% RH. Heat mat running under pot at ~25c.

Additional info:

Hey folks, I'm on D33 of my second grow and noticing some burning/bleaching tips. I think it might be caused by my light but I'm not sure. It's relatively minor and not too concerning but I want to nip it in the bud, so to speak. From my understanding N toxicity has similar symptoms, but usually starting at the leaves lowest on the plant. This is happening at the canopy. I've never used Biotabs before and I'm not sure if I should have added one tab then another after a week or so, I just crammed 1.5 in on day 17 about 5-10cm down. I think I may have staggered them but I can't remember.

Plant had a rocky start. I had been running the light way too low for weeks 2 and 3, about half the recommended power. I had somewhat slow growth and bumped the power up on the advice on an AFN member. So for the last 2 weeks or so my PPFD reading at canopy height was increasing up to 500, giving me a DLI of 43ish. From my reading I think this is a bit much for this stage of the plant but I can't find much solid evidence relating to autoflowers specifically and DLI levels.

I had the light about 15 inches from the canopy up until this point. Does the light height matter much if your PPFD readings are ok? I understand heat is an issue the closer you get, but is PPFD 500 at 15 inches and 15 feet effectively the same, or is there some other factor at play? I can hold my hand about 4 inches from the light before noticing much heat, so 15 should be plenty.

I have since altered the light slightly, it is now about 18 inches above the canopy with a PPFD of 400ish, for a DLI of 34.5. I am hoping that by reducing the power I can limit further damage, and continue to bump it up in a week or so. Thoughts? I plan to stick to this chart I found on the horticulture lighting group website, assuming I am at the far end of "veg" now, as the plant is throwing out pistils all over the place.

LIGHT INTENSITY REQUIREMENTS

Seedlings, Clones	Under 100 PPFD
Veg, Greens	150 PPFD - 400 PPFD
Extended Veg with healthy plants	350 PPFD to 500 PPFD
Flowering, Fruits	400 PPFD to 800 PPFD
Flowering with Supplement CO2	600 PPFD to 1100 PPFD

Images below to show the damage I'm asking about and plant as a whole. Any help or advice appreciated. Also welcome any info regarding DLI/PPFD as they relate to autoflowers specifically!

Edit to add: notice from looking at the pics that there is some cupping of leaves near the top as well, possibly confirming the light has been running too high?

 

[Mañ'O'Green]

@SecretFarmer Welcome to AFN The tip burn you are seeing is not from the LEDs. Light burn from LEDs is a fable. It does not happen. What you are looking at is you have reached the maximum strength nutrients in the pot that the plant can tolerate. The next step is a lock-out due to excessive nutrients in the pot.

Light mix fertigation should be PH to 6.3 going in. You should shift to a pattern of fertigate, water, water, water repeat to lower the nutrients in the pot.

24/0 light schedules produce low quality crops 18/6 is the best for autos.

 

[Couch_Lock]

Good info, MOG.

Here I've been running my autos 24/7....yikkes

Turned off the HLG 550V2 Rspec just now, maybe I'll shut it off 5 hours a day.

 

[Mañ'O'Green]

A long time ago before I came to AFN. I did a study with a buddy that wanted to go underground commercial with autos. The prime data was for energy usage and quality. Any how we could not do clones but we grew 6 plants in each grow from the same package of seed with all other things as close to the same as possible. 24/0 grew the biggest yield and two weeks faster, 20/4 was almost the same time frame but a little better quality. The 18/6 even though less yield the quality was so far superior it would command a higher price in the market (as long as you did not tell they were autos). It was also about 200 hours less power usage which was huge to this guy.

 

[SecretFarmer]

@SecretFarmer Welcome to AFN The tip burn you are seeing is not from the LEDs. Light burn from LEDs is a fable. It does not happen. What you are looking at is you have reached the maximum strength nutrients in the pot that the plant can tolerate. The next step is a lock-out due to excessive nutrients in the pot.

Light mix fertigation should be PH to 6.3 going in. You should shift to a pattern of fertigate, water, water, water repeat to lower the nutrients in the pot.

24/0 light schedules produce low quality crops 18/6 is the best for autos.

Thank you so much for your reply, it is great to have such knowledgeable folks to lean on in my noob stage!

I went off and did some more research after reading your posts. Based on my reading the consensus for light cycles with autos seems to be that some darkness is definitely preferable - which makes sense to me, the plant is a living organism and the ruderalis genetics have evolved on a daily cycle of light. I really appreciate you sharing your anecdotal experience and it seems that anecdotes are all that can be found on this topic. I hope some smart people do some in-depth studies into this in the future, it would be interesting to see the results. Our autoflowering friends seem to get left by the wayside in regards scientific study, but as cannabis becomes less taboo worldwide I hope we can see somethng in this area. I am currently a student of science myself, so maybe this a career path for me...

I mean this in the most polite way possible: I am going to disregard your advice re: lighting and continue to run 24/0. The reason being I am currently living through a severe cold snap here in my country with lights off temps easily falling below 15c and lower. The lights staying on all day keep a consistent temp for the plant. Installing a heater is not an option in my tiny tent, and the heat mat which I have isn't sufficient to keep the ambient temps up. From my thermostat reading the soil is remaining a somewhat consistent 20/21c. I feel like the potentially reduced quality yield from runnning 24/0 will be less detrimental to the plant's health than ~10c temp swings between lights on and off. Time will tell, as I get some more grows under my belt I will try different cycles and see what works best.

Further to my research it seems I am a bit boned with potential over ferting with biotabs specifically. I found some threads on other forums where people ran into similar problems with biotabs, where they flushed with plain water. This only seemed to exasperate the problems with biotabs, as the slow release ferts saturate the entire pot when flushing, it seems. So I am in a bit of a pickle. I'm gonna just let it run as it is. I am considering another feed of "Bactrex" which is, from the biotabs website:

• Has beneficial soil bacteria for the root system.
• Contains Trichoderma genus mould .
• Provides protection against root pathogens.
• Converts organic matter into nutrients.
• Certified 100% Organic.

Maybe my little microscopic friends can help mitigate any further damage but I will wait a few days and see what develops before making rash feeding decisions. For now it is plain water pH'd to 6.3 as you suggested, and I may give a mini flush of sorts. My watering so far has not been to 10-20% runoff, maybe just 1-2%. That's another disputed area of growing as far as I can tell, whether or not to water to run off in organic soil. Both sides of the argument make sense to me on a logical level. Anyway, hopefully the organic nature of the feeds will allow the soil conditions to return to normal.

FWIW, I have raised my light and lowered the power as mentioned, and as far as I can tell the damage has not developed too much further since yesterday. One big takeaway from my research into light cycles is that, while 24/0 may not be massively detrimental to a healthy plant and more a case of diminishing returns on g per watt, it will magnify any issues in a less than 100% plant. Maybe backing the light off a bit will give the plant a chance to recover. Again, not discounting your knowledge and experience in this regard, just taking another path as it lays before me.

Thanks again for your input, and I hope it come across that I am truly grateful and respect your opinion - but in the situation I am in now I am going to experiment and see what happens.

I may well be back begging for more help in a week's time.

 

[Couch_Lock]

I was only able to shut off my light for 2 hours last night. Tent temps had dropped to 64 Fahrenheit, after I witnessed that the light is back on.

Best I can do, this time of year, in upstate NY is likely cut the light off 2-3 hours a day.

I'm in a cold basement 57 to 59 Fahrenheit with a 400 watt heater (tiny) outside the tent, about a foot away from a port hole. With the HLG 550 V2 Rspec on at 100%, 36 inches away AND the 400 watt heater on 24/7. My max tent temp is 77 Fahrenheit, I like to keep the minimum temp at 64 or above.

 

[sickzone]

I was only able to shut off my light for 2 hours last night. Tent temps had dropped to 64 Fahrenheit, after I witnessed that the light is back on.

Best I can do, this time of year, in upstate NY is likely cut the light off 2-3 hours a day.

I'm in a cold basement 57 to 59 Fahrenheit with a 400 watt heater (tiny) outside the tent, about a foot away from a port hole. With the HLG 550 V2 Rspec on at 100%, 36 inches away AND the 400 watt heater on 24/7. My max tent temp is 77 Fahrenheit, I like to keep the minimum temp at 64 or above.

i feel your pain man.
i'm struggling with lights off right now.
i hate running my 1500w heater and still only at 63.5 with lights out.
next few days are going to be worse.
Are you in flower right now?
is there much effect to the flower with autos if you change up the schedule a few days.

 

[Couch_Lock]

I'm in early veg....Plants hit the growlight on Feb 1st

12 to 17 days old:

 

[Mañ'O'Green]

Thank you so much for your reply, it is great to have such knowledgeable folks to lean on in my noob stage!

I went off and did some more research after reading your posts. Based on my reading the consensus for light cycles with autos seems to be that some darkness is definitely preferable - which makes sense to me, the plant is a living organism and the ruderalis genetics have evolved on a daily cycle of light. I really appreciate you sharing your anecdotal experience and it seems that anecdotes are all that can be found on this topic. I hope some smart people do some in-depth studies into this in the future, it would be interesting to see the results. Our autoflowering friends seem to get left by the wayside in regards scientific study, but as cannabis becomes less taboo worldwide I hope we can see somethng in this area. I am currently a student of science myself, so maybe this a career path for me...

I mean this in the most polite way possible: I am going to disregard your advice re: lighting and continue to run 24/0. The reason being I am currently living through a severe cold snap here in my country with lights off temps easily falling below 15c and lower. The lights staying on all day keep a consistent temp for the plant. Installing a heater is not an option in my tiny tent, and the heat mat which I have isn't sufficient to keep the ambient temps up. From my thermostat reading the soil is remaining a somewhat consistent 20/21c. I feel like the potentially reduced quality yield from runnning 24/0 will be less detrimental to the plant's health than ~10c temp swings between lights on and off. Time will tell, as I get some more grows under my belt I will try different cycles and see what works best.

Further to my research it seems I am a bit boned with potential over ferting with biotabs specifically. I found some threads on other forums where people ran into similar problems with biotabs, where they flushed with plain water. This only seemed to exasperate the problems with biotabs, as the slow release ferts saturate the entire pot when flushing, it seems. So I am in a bit of a pickle. I'm gonna just let it run as it is. I am considering another feed of "Bactrex" which is, from the biotabs website:

• Has beneficial soil bacteria for the root system.
• Contains Trichoderma genus mould .
• Provides protection against root pathogens.
• Converts organic matter into nutrients.
• Certified 100% Organic.

Maybe my little microscopic friends can help mitigate any further damage but I will wait a few days and see what develops before making rash feeding decisions. For now it is plain water pH'd to 6.3 as you suggested, and I may give a mini flush of sorts. My watering so far has not been to 10-20% runoff, maybe just 1-2%. That's another disputed area of growing as far as I can tell, whether or not to water to run off in organic soil. Both sides of the argument make sense to me on a logical level. Anyway, hopefully the organic nature of the feeds will allow the soil conditions to return to normal.

FWIW, I have raised my light and lowered the power as mentioned, and as far as I can tell the damage has not developed too much further since yesterday. One big takeaway from my research into light cycles is that, while 24/0 may not be massively detrimental to a healthy plant and more a case of diminishing returns on g per watt, it will magnify any issues in a less than 100% plant. Maybe backing the light off a bit will give the plant a chance to recover. Again, not discounting your knowledge and experience in this regard, just taking another path as it lays before me.

Thanks again for your input, and I hope it come across that I am truly grateful and respect your opinion - but in the situation I am in now I am going to experiment and see what happens.

I may well be back begging for more help in a week's time.

I would avoid doing a flush if you can. It really upsets the root biome and I consider it a last resort for a dying plant. It often make things worse.

I would aslo avoid adding Bactrex or anything like Recharge at this time. These microbe and carbohydrate additions ramp-up the available nutrients to the plants and you already have too much.

 

[SecretFarmer]

I would avoid doing a flush if you can. It really upsets the root biome and I consider it a last resort for a dying plant. It often make things worse.

I would aslo avoid adding Bactrex or anything like Recharge at this time. These microbe and carbohydrate additions ramp-up the available nutrients to the plants and you already have too much.

Plain water and bed rest until she improves! Thanks Man O Green. I will update this and my diary in the "Indoor Grow" section. I think she will make it.

No worrying signs during this evenings check up and no major development of symptoms, but I'm gonna hold off on watering until tomorrow as theres still some weight to the pot.