downward leaf curl

[MisterAvocado]

Greetings farmers, I'd appreciate your help diagnosing an issue with a few of my girls.

• strains: super silver haze, grandaddy purps
• age: 2 weeks post-flip
• media: perlite/coco (Botanicare ready-gro)
• nutes: botanicare line with calmag, liquid karma, hydroplex; 2.0 EC, pH 5.8.
• feeding: daily handwater, drain to waste.
• environment: sealed 8k vertical, 50% RH, 80-85F temp, CO2.

Flushing with pH 5.5, I'm getting a runoff pH of 6.5; runoff had no significant increase in EC. I've read differing opinions on whether runoff pH is useful metric with coco.

I suspect that the issue is N toxicity or general overfeeding. What do you all think?

 

[kushtrees]

lower your temps or up your humidity, usually environmental factors cause problems like that for me. if your humidity is at 50% then you want your temps below 80F, otherwise youll get VPD issues. Ive never had any luck with pH of coco run off telling me anything. You could lower your EC a little, but it doesnt look like N toxicity to me, the tips usually curl down more, not just the sides, looks more like humidity needs to be higher

 

[growdamnit]

doesn't look over fed to me.. try watering every other day or every 2 days.. it's always a good thing to stress plants a little.. good luck homes..

 

[Bublonichronic]

looks a little overwaterd maybe?

 

[hiboy]

you could be root bound, , transfer to a larger container , also if your runoff is a whole dig higher thats def is not good, flush a few times thouroghly,
how often are you watering?
hb

 

[MisterAvocado]

you could be root bound, , transfer to a larger container , also if your runoff is a whole dig higher thats def is not good, flush a few times thouroghly,
how often are you watering?
hb

Definitely not root bound now, although some of them probably will be in a few weeks. I've been watering daily. A few days ago, I flushed them all and lowered the ec of my standard feed to about 1.5. I flushed a few today with 0.5ec solution and saw runoff of 1.5-2.0 ec. So maybe that's my problem. Perhaps I need to increase my runoff in daily feeding.

re temp/RH: I will have a new AC installed by end of week so can bring temps down a bit more. I don't really want to increase my RH much more since I always have girls in weeks 6-8 in this room.

re the overwatering theory: I had the same thought early on, but here is why I don't think it's right:
I see the same problems on some girls in 10+ gal pots (which do not dry out between waterings) as I do on girls in smaller pots (which get pretty dry between waterings).

 

[Seamaiden]

They appear to be heat stressed. However, the temps you report should not be causing what you're showing.

Honestly, knowing what I do about VPD, but not in the presence of CO2, I want to suggest raising the humidity, up into the 60%+ range, but I honestly don't know how the plants would react in the presence of CO2 dosing.

If vapor pressure deficit is terribly out of range, and yours is at 1.74 kPa -- 2.05 kPa, then leaf turgor is quite affected, could possibly cause what you're observing. Try to get it closer to .85 kPa if you can.

Learn about it here: http://www.autogrow.com/1_information/1_vpd/info_vpd.html
Calculate yours here: http://www.autogrow.com/vpd_calc.php

 

[Chobble]

Like everyone says, its to damn hot in there. You really want your grow room to be around 75 degrees, that's where your plants will grow the best.

Also feeding the SLH half of what you feed the GDP is a very good idea as well.

 

[Unit541]

It's not simply too hot. Like Seamaden mentioned, it's too hot for the humidity level. If you're going to keep the RH at 50%, you've got to get the temps down to the low 70s. They'll grow stronger and faster at 80-85, but to be happy in those temps the RH needs to be up near the 70% range.

Play with the calculator Seamaden linked to. It'll illustrate how the two figures (temp and RH) go hand in hand.

 

[Chobble]

It's not simply too hot. Like Seamaden mentioned, it's too hot for the humidity level. If you're going to keep the RH at 50%, you've got to get the temps down to the low 70s. They'll grow stronger and faster at 80-85, but to be happy in those temps the RH needs to be up near the 70% range.

Play with the calculator Seamaden linked to. It'll illustrate how the two figures (temp and RH) go hand in hand.

I understand this, but he's in flower your RH should be around 50% when in flower. Thus why you want your room temp to be at about 75.

 

[growdamnit]

shouldnt leaves curl upwards if it was heat stress?
if it is too hot I havent seen leaves curl like that during heat stress..
to me those leaves really says over waterd..

 

[Unit541]

I understand this, but he's in flower your RH should be around 50% when in flower. Thus why you want your room temp to be at about 75.

2 weeks in is nowhere near far enough along in flower to start dropping the humidity.

 

[Seamaiden]

First, I should qualify that everything I'm about to say is my experience, which is not like that of others. I've had the best runs keeping flowering RH >50%, closer to 60% is much better (even higher RH values, read some of what Jalisco Kid has written on the subject). I keep vegging plants typically much higher. This is with specific regard to indoor growing.

Second, what I see is exactly like the worst heat stress I've seen, in all plants, not just cannabis. The plant is turning leaves inward and under in order to conserve moisture and reduce its profile (heat catching surface area).

Third, I've found that the larger the plant, the greater variation in VPD values it can tolerate. Also, the larger the plant, the less the RH, and therefore VPD, varies.

Fourth, dude's running CO2, which should allow the plants to tolerate higher heat, but if I understand anything about it, should also allow (require?) higher RH levels.

HTH.

 

[Unit541]

Right on Seamaden, your conclusions about RH are right in line with my own, also based on personal experience. The only time my hygrometer reads 50%, is when I'm drying buds. I keep it in the high 70's in veg, and most of flower. Last 3 weeks or so, I begin dropping it gradually to about 60%. This is also when I increase my EC rather sharply. High EC is the only way to simulate drought in hydro (can't exactly stop giving them water...), and I've found that this produces a final bump in oil and resin production.

With CO2 enrichment, I've found 90 - 93 degrees F and 80-85% RH really allows them to put the peddle on the floor. Adding CO2 increases the plants overall metabolism, meaning it can handle more of everything, nutes included.

 

[monkeymun]

It definitely appears to be heat stress to me too.

 

[Darth Schwag]

Check your root ball for boundedness. My Master Kush were dripping wet long after the soil had dried out. They could be indicating overwatering due to root bind. When mine did dry out the nutes started burning the leaf margins.

 

[WalterWhiteFire]

I have never had VPD issues like that at 50%RH 85 degrees with a fully enriched environment 1500ppm, Not arguing that they might grow better at 60%... To me i would have to guess over watering...

 

[MisterAvocado]

I've upgraded my ACs and am now running 75F and 55% RH during lites on. I will provide a report in a few days. I have additional cooling on order, so that I can run in the low 70s.

Assuming the leaf curl was heat-related, should I expect to see the curled leaves recover?

 

[LexLuthor]

If it was heat related and cooled the room down then you shouldn't get anymore leave curls, as for the ones already curled I'm not sure.

 

[Seamaiden]

I've upgraded my ACs and am now running 75F and 55% RH during lites on. I will provide a report in a few days. I have additional cooling on order, so that I can run in the low 70s.

Assuming the leaf curl was heat-related, should I expect to see the curled leaves recover?

Yes, unless VPD values are still too far out of range. Remember, the curling inward is a response to losing moisture too rapidly. Unless it's a rhododendron, then it's often a response to too cool conditions. You growin' rhodies also, perchance?