Extreme clawing /browning / drying of leaves

[sillybilly123]

New here, very inexperienced grower. This'll be a long one as people seem to really want all the info, so thanks for your time.

I'm using a Viparspectra KS3000, drawing 320W. Ambient temps mostly between 25 -30° with lights on, 20 - 25° lights off. Running 18-6, turning lights off in the middle of the day in summer ATM to avoid that 30-35° range in my attic at peak temp. Although recently there have been some warmer temperatures hit (usually 30-32°, sometimes as high as 35 for very short bursts). Humidity consistently between 40-55%. Using canna bio terra plus soil which contains Coco and peat, among other things. It says it comes pre fertilised, so I've only fed them once with some organic 3-1-5, at half-strength. It has worked well on the other plants in the house. I've had the light about 2.5ft above them, although raised it today to about 3.5ft today. I started with no top layer, but after spider mites attacked I added the fly tape and the layer of grit, which has put a big dent in the population numbers. I read there may be some downsides to adding a top layer of grit such as blocking oxygen from reaching the roots, and absorbing heat and acting like a radiator. Would be interested to hear opinions about it.

I've got 2x big bud autos which are 7wk and 5wk old, doing great. Nice fat stinky buds. Also got 2x Amnesia auto which are 3wk and 1.5wk old, and both are showing extreme downward leaf curling, pics attached. The new growth on top is looking good, but then after a day or two the leaves are slowly shriveling downwards. I don't think it's overwatering - I've just been abroad for 4 days, and they haven't been watered, and upon my return the problem has got worse. I don't think it's underwatering either because I've been watering them every other day up until now. The fan isn't blowing straight onto them so I doubt it's wind burn, and they started curling before I fed them so I don't think it's nute burn.

It could be heat stress, because of the 30° + temperatures hit recently, but that seems a bit extreme to me as 90% of the time, it has been within that 25 - 30° range. The light has been quite low however, so maybe this plus the heat could be the culprit.

I should stress, the older big-bud auto plants are doing great under almost the exact same conditions. With one important difference. They started their lives for 2-3wks under a 250W Amazon light, until I upgraded to a 320W Viparspectra with a much higher PPFD rating 3 weeks ago. Is it possible that the Big Bud seedlings could have developed under the less intense higher-hanging lights and then when they were stronger they were able to handle the upgrade to the stronger light? Whereas the Amnesia Autos were under the low-hanging 320W light for their whole lives. The plants have been in the 750 -850 PPFD (40 - 45 DLI) range. I read this is quite high for seedlings, and autoflowers in general. I thought they should handle it as the big bud plants were flourishing.

I've raised the light so the PPFD is back down to the 450 region now, and temps are a bit lower. It shouldn't exceed 30 again.

Sorry for the long message, I figured I might as well put out all the info and actually give myself a chance of fixing the problem, and stopping it from happening again. Anything anyone can add is greatly appreciated

Thanks a lot

 

[Porky1982]

They are over watered and have nutrient lock out!
Pick one up and see how heavy it is!
You didn't put any information about how much and how often you water them!
When they look as sad as yours do they probably have root issues from being wet for to long!

 

[ThirtyThreeIV]

From what I can tell, you’re getting a nitrogen overfertilization that’s causing a couple tell tale issues. Too much nitrogen = the growth of small leaves, the claw shaped leaves, and stunted growth.

This excess of nitrogen may have changed the ph of your soil to something your plant doesn’t like as well.

It’s not the end of the world though, the tops of your plants look happy and that means the new growth is adjusting. I would personally remove the rock on top of your soil, as that tends to keep in moisture, and cannabis is a plant that really likes to chase water. If you have a slow drying medium your roots will get lazy and can develop rot, whereas a fast drying medium provides more oxygen to the roots and allows them to chase the water as it dries out.

 

[sillybilly123]

They are over watered and have nutrient lock out!
Pick one up and see how heavy it is!
You didn't put any information about how much and how often you water them!
When they look as sad as yours do they probably have root issues from being wet for to long!

That was my initial thought, and so I left them for 5 days to dry out. The pots felt very light however the problem persisted. I've been watering 2-3 times a week, when the top inch or two feels dry. Honestly I haven't been measuring how much water, just keeping it to around 50 ml every couple of days for seedlings, maybe 250 ml every 2-3 days during veg, and up to 500ml every 2-3 days for flowering, or until I get a drop out of the bottom. Trying to spread the water around the pot a bit as well.

 

[sillybilly123]

From what I can tell, you’re getting a nitrogen overfertilization that’s causing a couple tell tale issues. Too much nitrogen = the growth of small leaves, the claw shaped leaves, and stunted growth.

This excess of nitrogen may have changed the ph of your soil to something your plant doesn’t like as well.

It’s not the end of the world though, the tops of your plants look happy and that means the new growth is adjusting. I would personally remove the rock on top of your soil, as that tends to keep in moisture, and cannabis is a plant that really likes to chase water. If you have a slow drying medium your roots will get lazy and can develop rot, whereas a fast drying medium provides more oxygen to the roots and allows them to chase the water as it dries out.

I've removed the rocks, and you are right the soil looked moist. In theory my soil is fast drying. I'm going to let them dry out for a few days and then I'll give them a flush out to see if I can shift any nitrogen build up. After that I'll resume feeding, but I've ordered some better quality, low nitrogen nutrients now. I've also ordered a ph meter and som +/-. Any thing else you'd recommend?