I got some plants that have a number of leaves that are yellowing rapidly. But the rest of the leaves look nice and green. Once a leave begins to yellow it happens pretty fast (a couple days) and become "soft" when breaking off. i.e. they don't "snap" off - they just feel kind of mussy when you remove them (albeit the leave itself is normally - just yellow). All different strains (and I can't remember what is what). This is an organic outdoor grow in FFOF, 15 gallon pots. Plants are about 3 months old in various states of flower. I'm having to water almost every day (even though it's not been that hot - mid 70's) as the plants begin to droop. Weather has been really cool, overcast until 10-11am. Then in the mid 70's with nights in the 50's. They've been getting fert tea about once a week with bat guano (10-2-1 during veg .5-12-.2 during flowering). The tea also has worm casting, fish hydrolysate (2-4-1), kelp (1-.1-2), and rock phosphate (0-2-0) & molasses. Recently I've been giving them straight guano (no team). I don't worry about the ph much, but when I did test run off it was right around 6.8 - 7.0. Have used Excel LG & Actinovate for PM (which I haven't had on the plants, but is around in the yard), neem, and a BT for the evil moth worms that like to do a number on the plants every year. The plants are in various stages of flower, with some flowering real early (a month ago). I understand the flowering plants having yellow leaves. But the one plant showing the most yellowing (First three pics) is just starting to flower. No purple color (anywhere) on this plant. Pics 4 & 5 are of another plant. This also shows yellow but much further along not abnormal. Last pic is a group shot of several plants.
The leaves yellowing all over are showing Nitrogen deficiency. Larger plants need a higher ratio of N than average.
Plants will exhibit lack of vigor, slow growth and will be weak and stunted. Quality and yield will be significantly reduced. Older leaves become yellow (chlorotic) from lack of chlorophyll. Deficient plants will exhibit uniform light green to yellow on older leaves, these leaves may die and drop. Leaf margins will not curled up noticeably. Chlorosis will eventually spread throughout the plant. Stems, petioles and lower leaf surfaces may turn purple.