Today i found black patches on alot of my leaves, it on the outer edges of some leaves with some black patches on different parts of the leaves aswell. The strain is Big Bang (seed was feminized), I vegged for 2 weeks and am now flowering using a 12/12 light schedule, I'm currently on week 5 of flowering (flowering for 5 weeks 3 days to be specific). I water with about 250-500ml water when the soil is quite dry but still slightly damp. I'm not feeding it any nutrients/fertilizers, just plain water which leads me to believe that it is a deficiency of some sort. The unique thing about my grow is that it's very low wattage, 45w to be specific, it has been growing perfectly healthy since day 1 despite not having much light, so i don't think it's anything to do with light. I have attached pictures below, the pictures showing the black patches was taking using my camera phone and a jewellers loupe to magnify the image. Pictures #1, #2, #3 are of the black patches and #4 & #5 are to show the size of the grow area, I'm not using any fans as the size of the grow area is big enough to not be able to contain any heat (The grow area is essentially a desk with one side of it covered and the other open. Picture #1 Picture #2 Picture #3 Picture #4 Picture #5 If anyone has any idea on what it is that is causing this problem please let me know, this is my first grow and i don't want to ruin it as i have put in alot of time and effort.
I believe it's a phosphorus deficiency, I've had this problem and adding some nutrients with phosphorus seemed to help. Although don't take my word for it just yet ahaha.
That was my first thought although it looks more black than purple so i thought i'd put it on here to get other peoples opinions. Thanks for your reply aswell. Anyone else think that it may be a phosphorus deficiency.
That's nitrification. Too much available nitrogen when the leaves were formed, they will crisp up, dry out and fall off of the plant. You either have too hot of a soil, or too much nutrients in your water. If the soil is just regular soil and you are using nutes primarily from a bottle, just cut back by half.
skunk hit it right on the money. at first glance it looks like a potential P unavailability due to a pH issue. if it were a P deficiency, it would be coupled with at least some discolored stems. the nitrification also is causing the "clawing" of the leaves.
Woo! I love this forum; thank you skunk for sharing that. Now I know what that discoloration is, if found by itself.