Canoeing leaves

[cbdhemp808]

The plant is trying everything it can to slow down so its cupping its leaves to avoid light to slow PS.

Wow. I was going to guess the upper, young leaves were just too hot, from the Mars 300w light. This is the first I've heard of cannabis cupping leaves to slow photosynthesis. Very cool, thanks.

 

[VetSmoke85]

Very similar to a plant I have right now. I've raised the light a bit and after a couple of days the leaves seem to be curling less.

 

[bluter]

Very similar to a plant I have right now. I've raised the light a bit and after a couple of days the leaves seem to be curling less.

that happens outdoor all the time as well. not sure how you back off the sun lol.

it's usually more than one factor. light, heat, air movement, and rh, are all factors in canoeing. also overwatering, suffocating, and root stress plays a part.

Your RH is way to low. It should be at 55-60. Do a bit of reading on vpd.

i routinely grow at 25% rh with zero issues. i'm topping at 40% right now. i don't run in to this cupping unless it's combined with another issue.

those vpd charts can be misleading, different charts often contradict each other. it's a great way to sell gear though. if you live someplace that doesn't hit those conditions naturally it can get expensive trying.


i always grow through what i'm given. there's only so much you can manipulate in a cost effective manner.

 

[safeman]

Your RH is way to low. It should be at 55-60. Do a bit of reading on vpd. In a nutshell its the way the atmosphere drives your plant. At 45% your plants are running way to fast. The cupped leaves are from the plant being overdriven by the light for the humidity level you are at. The plant is a pump. It takes water from the soil which has nutes in it, pumps them up to the leaves, and uses the nutes for photosynthesis. After PS(photosynthesis) has happened the CO2 has been split. The plant keeps the C( carbon,sugar) and releases the O2 with the used water out the stomata on the underside of the leaves. When you lower the humidity it widens the RH gap between the inside of the plant (always 100% rh, as its full of water) and the room RH which evaporates that used water quicker, causing suction, for lack of a better term, and revs the plant. The light powers the PS and can also rev the plant by splitting CO2 faster and causing water to push out the stomata quicker. Room temp is also a factor but you are in the ballpark but in veg it should be a bit warmer. The plant is trying everything it can to slow down so its cupping its leaves to avoid light to slow PS. VPD will initially bend your brain but its actually quite simple. Read a bit on it and download a VPD calculator from the app store but get one that has 3 inputs not 2. It should allow room temp, leaf temp, and RH to be input. You will need an infrared thermometer to take the leaf temp. Moving the light closer raises leaf temp and farther away lowers leaf temp. When the light is at the correct height the leaves should be 2 degrees cooler than the air. Thats what the plant wants. 2 degrees is perfect for that transpiration out the stomata that I mentioned. As for the hungry look it could need a feeding but..... with the plant revving so fast you may simply not be able to provide it enough calories for the speed its running at and it appears to be starving, even tho its got enough food. It doesnt have enough feeder roots( the roots poking out bottom will be water roots) to supply enough food for the pace its running at. You wont know for sure if its out of food or simply running to fast until you fix your vpd. At 75 degrees you need 58% humidity for a good veg speed, and then move the light or dim/brighten it until the leaf temps at the top of the plant are pretty close to 2 degrees lower. I say pretty close because lower tops may not be optimal but the highest top is stressed the most so you need to cater to it. Get the main cola dialed. The vpd calculator will allow you to run scenarios so you can decide which route to go, as in lowering light or changing rh, etc as the plant progresses. Also find a vpd chart, theres a ton online, one for cannabis, and it will guide you for your vpd levels as the grow progresses to flower. VPD sounds complicated but its actually really easy once you get it so just read a bit on it. The plant, when it runs too fast, is sweating. Like humans, excessive sweating can require extra magnesium. I would also give it a light feeding, and I do mean light, as per the mixing instructions, of Cal-Mag. Its a great rescue tool as the mag always helps but the calcium, which most people think is a nute, and it is, also sets the EC of the soil and electrically opens the soil up to allow air in. Tight soil can easily mimic overwatering as water cuts off air too so tight soil and overwatering can look the same. Use cal mag gently. low doses more often will be wayyyyyy more beneficial. Too much Cal will raise the EC too high and fry the plants. Earthworm castings are a fantastic source of bio-available calcium. Calcium is heavy so it always goes down and eventually out with the runoff so topdressing regularly with EWC( Earth Worm Castings) will keep fresh proper calcium up top trickling down.

So in a nutshell...
1 Raise your RH to 58-60.
2.Give Cal-Mag.
3.Learn VPD basics to get the light at the right height.
4.Get some EWC.
Then... if your plant still has a problem it will be really easy to diagnose without any tail-chasing. Also dont judge your plants future by the state of the damaged leaves as they have scars now, only watch the new growth or for new problems on the older leaves, but the scars that are already there wont go away. Its not a big deal because by the time you start flower most of the scarred leaves will be defoliated. It doesnt really look hungry as its not cannabalizing itself. Sorry theres no short answer but you caught it and its an easy fix with only basic vpd knowledge. Blackstrap mollasses is a great source of calcium, magnesium, potassium, iron, and a whole lot more. Its cheap and it works but right now I would use the Cal-Mag as its stronger. Moving forwards any time your plant looks like it needs a pick-me-up some molasses will always help. Just dont feed it regularly. It will make the soil biology stop eating soil and only target the mollasses, but every couple weeks wont do any harm. Too much can also change the taste of the weed.

great read- thanks !!! VPD is a great way to cultivate believe "jungle Boys" swear about this method of growing

 

[Gee64]

that happens outdoor all the time as well. not sure how you back off the sun lol.

it's usually more than one factor. light, heat, air movement, and rh, are all factors in canoeing. also overwatering, suffocating, and root stress plays a part.






i routinely grow at 25% rh with zero issues. i'm topping at 40% right now. i don't run in to this cupping unless it's combined with another issue.

those vpd charts can be misleading, different charts often contradict each other. it's a great way to sell gear though. if you live someplace that doesn't hit those conditions naturally it can get expensive trying.


i always grow through what i'm given. there's only so much you can manipulate in a cost effective manner.

yeah thats why i told him to read a bit on vpd. Its a 3 prong thing so if humidity is low you can still make light height or room temp as other variables. Do you start your seedlings at 25% RH or do you dome them?

 

[Gee64]

Very similar to a plant I have right now. I've raised the light a bit and after a couple of days the leaves seem to be curling less.

Vet shes in deep Buddy. Whats your RH at the canopy level? whats your room temp? Do you have an IR thermometer? She is too close to the light for the RH of your room for the size of her rootball. The canoeing is her trying to stop photosynthesis. The chlorosis is her roots not being able to supply enough nutes and mostly O2 so she appears to be choking and hungry. I would raise the light at least 18 inches, then with the IR thermometer slowly, after 48 hours up high, lower that light back down until the leaves at the top are 2 degrees cooler than the room temp at canopy level. Also your RH looks really low. It should be at least 55% for her stage of life. She looks like she is sprinting a marathon and running out of hydration and just starting to run out of calories. She needs a couple days off to relax and rehydrate. When the light gets too close she speeds up. When the RH gets too low she speeds up. Her roots cant keep up to the pace so she canoes and runs out of breath.

 

[bluter]

yeah thats why i told him to read a bit on vpd. Its a 3 prong thing so if humidity is low you can still make light height or room temp as other variables. Do you start your seedlings at 25% RH or do you dome them?

i never dome seedlings only clones under any conditions. seedlings naturally harden off to the conditions in which they are started. it will affect how fast they develop though.

i monitor temp and rh in the grow spaces, but only manipulate air flow and extraction to change them. adding layers of humidifiers, dehumidifiers, ac, c02, becomes a pandoras box. you'll never spend enough. i do get why some enjoy it though. it's a lot like the model train sets folk will start building only to have the thing take up an entire basement over time.

 

[Gee64]

i never dome seedlings only clones under any conditions. seedlings naturally harden off to the conditions in which they are started. it will affect how fast they develop though.

i monitor temp and rh in the grow spaces, but only manipulate air flow and extraction to change them. adding layers of humidifiers, dehumidifiers, ac, c02, becomes a pandoras box. you'll never spend enough. i do get why some enjoy it though. it's a lot like the model train sets folk will start building only to have the thing take up an entire basement over time.

I live in a desert so 35% is about the muggiest day of the year here. I circumvented all the costly stuff simply by putting a flood tray on the bottom of my tent and filling it with an inch of water when it runs dry I put my smart pots on upside down milk crates and water right thru them where they sit. I bought one controller to turn my exhaust fan on when humidity gets too high. Cheap easy and very effective. In flower the extra ventilation to get RH under 50% also lowers my temps a bit so it really works well.

 

[Gee64]

My seedlings in the ground do just fine but indoors I need to dome them. Clones I cut in coco need doming, the ones I do in the Kloneking don't.

 

[bluter]

I bought one controller to turn my exhaust fan on when humidity gets too high. Cheap easy and very effective. In flower the extra ventilation to get RH under 50% also lowers my temps a bit so it really works well.

moving air is always the cheapest way to control an environment and the first place to start. my pops worked in commercial hvac for years and it's a rule in that world as well. he's also designed a few grow rooms for folk.

 

[VetSmoke85]

Vet shes in deep Buddy. Whats your RH at the canopy level? whats your room temp? Do you have an IR thermometer? She is too close to the light for the RH of your room for the size of her rootball. The canoeing is her trying to stop photosynthesis. The chlorosis is her roots not being able to supply enough nutes and mostly O2 so she appears to be choking and hungry. I would raise the light at least 18 inches, then with the IR thermometer slowly, after 48 hours up high, lower that light back down until the leaves at the top are 2 degrees cooler than the room temp at canopy level. Also your RH looks really low. It should be at least 55% for her stage of life. She looks like she is sprinting a marathon and running out of hydration and just starting to run out of calories. She needs a couple days off to relax and rehydrate. When the light gets too close she speeds up. When the RH gets too low she speeds up. Her roots cant keep up to the pace so she canoes and runs out of breath.

Humidity is 70-85%. I've raised the light and increased fresh air coming into the tent. She's grown much faster than the rest in the tent (double the size). The other 3 are raised on upturned pots. The Gushcake in the back right has a little strop every now and then too. I'll raise the light a little more tonight and see how they respond over the next few days. Cheers.

 

[bluter]

Humidity is 70-85%. I've raised the light and increased fresh air coming into the tent. She's grown much faster than the rest in the tent (double the size). The other 3 are raised on upturned pots. The Gushcake in the back right has a little strop every now and then too. I'll raise the light a little more tonight and see how they respond over the next few days. Cheers.

have you flipped cause they definitely wanna bust out ..

they look good vet. could maybe use a thinning underneath. curl could be it be having a little trouble transpiring with the rh that high. indica leaners grow a touch better on the drier side. it's just the new stuff, and pulling the light a bit will help.

 

[VetSmoke85]

have you flipped cause they definitely wanna bust out ..

they look good vet. could maybe use a thinning underneath. curl could be it be having a little trouble transpiring with the rh that high. indica leaners grow a touch better on the drier side. it's just the new stuff, and pulling the light a bit will help.

Yeah I flipped them a week ago. I'll do a bit of defol when they've finished stretching. Thin them out a little and get rid of anything with low potential. Hopefully that'll reduce the humidity a little and I can bump the extraction up a bit more. I'll add a couple more USB fans for air movement too. The Peanut Butter Cookies and Original Cheese in the middle seem happy thankfully.

 

[bluter]

Yeah I flipped them a week ago. I'll do a bit of defol when they've finished stretching. Thin them out a little and get rid of anything with low potential. Hopefully that'll reduce the humidity a little and I can bump the extraction up a bit more. I'll add a couple more USB fans for air movement too. The Peanut Butter Cookies and Original Cheese in the middle seem happy thankfully.

what are your temps like ? the extra rh will hold heat during lights on, but cools like a bitch in northern climates when they go off.

rh that high gets in to mold territory later in flower, especially if you get a swing in temps and can't dry it out.

i'm betting the curl you have is rh / temp reaction.

 

[Delps8]

Wow. I was going to guess the upper, young leaves were just too hot, from the Mars 300w light. This is the first I've heard of cannabis cupping leaves to slow photosynthesis. Very cool, thanks.

Photosynthesis is a reaction to inputs - CO2, photons, and O2.

The idea that plants would take action to slow photosynthesis raises questions such as what mechanisms are used to make that determination and, second, why would a plant want to decrease the amount of glucose it is generating?

While I don't know the conditions that lead up to the leaves cupping, I wouldn't base is on the idea that the plant is making a decision to change the rate of photosynthesis.

 

[VetSmoke85]

what are your temps like ? the extra rh will hold heat during lights on, but cools like a bitch in northern climates when they go off.

rh that high gets in to mold territory later in flower, especially if you get a swing in temps and can't dry it out.

i'm betting the curl you have is rh / temp reaction.

Around 24C. Oh yeah, I know that's gotta come down when they're into full flowering. Few tweaks and she'll be reyt I'm sure.

Didn't mean to hijack your thread @Cheschire. Useful inputs for both of us though. Cheers.

 

[cbdhemp808]

Photosynthesis is a reaction to inputs - CO2, photons, and O2.

The idea that plants would take action to slow photosynthesis raises questions such as what mechanisms are used to make that determination and, second, why would a plant want to decrease the amount of glucose it is generating?

While I don't know the conditions that lead up to the leaves cupping, I wouldn't base is on the idea that the plant is making a decision to change the rate of photosynthesis.

Good point... I like that. Further, people run lights 24 hrs. and no cupping, right? I think it's heat.

I'm not an indoor grower, so y'all have way more experience than me on this issue. But I do have experience with leaves cupping/canoeing in my greenhouse during the summer, when temps were getting to 95°F and above in there. We have very high humidity in our tropical location here in Hawaii, all the time. Right now it's 87%, and we have bright sun today.

The overheating happened in 2020, and I'm not using that greenhouse at the moment – it needs to be outfitted with a ridge vent to release heat. I'm using two smaller greenhouses (one veg, one flower) that are specifically designed for max air flow and release of heat.

 

[Delps8]

Good point... I like that. Further, people run lights 24 hrs. and no cupping, right? I think it's heat.

LED's don't generate heat the way that gas discharge lights do so it's not easy to cause heat stress if you're using an LED.

I'm not an indoor grower, so y'all have way more experience than me on this issue. But I do have experience with leaves cupping/canoeing in my greenhouse during the summer, when temps were getting to 95°F and above in there. We have very high humidity in our tropical location here in Hawaii, all the time. Right now it's 87%, and we have bright sun today.

The overheating happened in 2020, and I'm not using that greenhouse at the moment – it needs to be outfitted with a ridge vent to release heat. I'm using two smaller greenhouses (one veg, one flower) that are specifically designed for max air flow and release of heat.

Yeh, 95° and not able to control RH is tough for a lot of plants. At 95°, you'll want RH to be about 70% in flower - isn't that what they call a "dry" in HI?

 

[cbdhemp808]

LED's don't generate heat the way that gas discharge lights do so it's not easy to cause heat stress if you're using an LED.

A 600w HPS generates the same BTUs of heat as a 600w LED. LEDs are more efficient, so you get more light per watt. LEDs apparently produce about half as much radiant heat as HPS.

Black Dog LED has a detailed article regarding all this. In the article they compared leaf temperature for 1000w HPS vs. 750w LED, at 24" above plants. The result was the HPS raised the leaf temp 13.7°F above ambient 75°F, resulting in 88.7°F (which is above the recommended 86° max). The LED raised the temp 6.3°F, resulting in 81.3°F. When ambient temp is 84°F, both the HPS and the LED raise the leaf temp above 86°.

RE: The OP's Mars Hydro 300w LED...

The light is 32" from top of tallest plant, I also only have the light % set on 50% strength, my ppf meter says everything is in the proper settings and height.

I can't see how that would generate >86° leaf temp at 70-75° ambient temp. Now I don't think the cupping/canoeing could be from heat.

Yeh, 95° and not able to control RH is tough for a lot of plants. At 95°, you'll want RH to be about 70% in flower - isn't that what they call a "dry" in HI?

I've never seen our humidity that low!

So, was the OP's cupping/canoeing mainly the result of not enough humidity? He's running 45-55, and you are recommending 55-60? That's not a big difference, right?

 

[Delps8]

A 600w HPS generates the same BTUs of heat as a 600w LED. LEDs are more efficient, so you get more light per watt. LEDs apparently produce about half as much radiant heat as HPS.

Black Dog LED has a detailed article regarding all this. In the article they compared leaf temperature for 1000w HPS vs. 750w LED, at 24" above plants. The result was the HPS raised the leaf temp 13.7°F above ambient 75°F, resulting in 88.7°F (which is above the recommended 86° max). The LED raised the temp 6.3°F, resulting in 81.3°F. When ambient temp is 84°F, both the HPS and the LED raise the leaf temp above 86°.

I think it's conventional wisdom that LED growers will want to increase ambient temps by 10° compared to HPS.

RE: The OP's Mars Hydro 300w LED...

I can't see how that would generate >86° leaf temp at 70-75° ambient temp. Now I don't think the cupping/canoeing could be from heat.


I've never seen our humidity that low!

So, was the OP's cupping/canoeing mainly the result of not enough humidity? He's running 45-55, and you are recommending 55-60? That's not a big difference, right

Yes, the entire range of 45 to 60 is either Optimal or Next to Optimal in terms of VPD so I suspect it's one or more of the other factors that others have posted.

After monitoring VPD for three grows in a 2' x 4' in an unheated garage in SoCal, I'm getting to the perspective that you're never going to get RH spot on. We're dealing with plants giving off water and air currents in the tents and around the plants that set up their own "micro climates". Readings taken just a few moments apart will be different and the values will be different a foot or two or three away. The AC Infinity controllers give a real time read out of temperature and RH and the RH changes all the time. When it's "stable" it's still about a 3% or 4% range.

Add in the fact that most of the hygrometers we use are accurate to ±5% so even the accuracy of RH is iffy.