Me and my other novice grow buddy have been arguing that the yellowing that occurs late in flower is just from the plant sucking nutrient out of the leaves even while still maintaining the feed schedule My thought is that the yellowing occurs once flush has started (last 2 weeks) and the plant is taking all the nutrient out of the leaves because there is little to none left in the grow medium. Please help settle this.
Technically, yellowing can be caused by either. It's much less likely to be caused by the flushing because the final flush before harvest shouldn't and usually isn't performed long enough before harvest for significant leaf damage to appear. The plants have to spend enough time growing without food to feed on themselves enough to display much damage. They also don't grow as much in the last two weeks as they do in earlier weeks. They usually do more ripening than growing. Unless you're referring to just a couple leaves yellowing a little at their tips in the last few days of their life, it's not caused solely by the flush you perform just two weeks before harvest. However, any deficiencies causing leaf damage would still be exacerbated by flushing. So, your friend being right must also mean that you're right as well, at least to some degree. What's more important is that no yellowing needs to occur in the plant's lifetime. A plant's nutrient requirements increase with size. During flowering, fertilizer concentrations should be steadily increased as it grows taller and its buds grow larger. A more aggressive increase in fertilization as your flowering periods progress would increase your yield and probably make for more beautiful buds at harvest.
I appreciate the input. From all the beginner literature i have read pointed towards saying the plant will yellow a bit towards the end of the flower cycle. So what are you saying is that it shouldn't happen if the right feeding had occured throughout the plants flower cycle and/or life? I love your signature by the way.
The yellowing is due to a depleation of N in the plant. The nutrients that most people feed their plants during flower is low in nitrogen and higher in other nutrients to aid in flower production. Nitrogen is used more in leaf growth and isn't needed as much in flowering, and it can make your buds taste bad and smoke harsh. That's why we don't use much in flower. But it's a delicate balance between using just enough N and not enough, IMO. I don't like to see yellowing too early in flower and will feed a little veg nutes every now and then to keep my plants looking healthy.
Actually the yellowing is likely to happen regardless of how you feed and whether or not your flush, or when. As others have said, the yellowing is due to a nitrogen deficiency, which you want because N can retard bud production. That is precisely why you use a different fert for flower than for veg, the big difference between the two being the N level. I usually see yellowing start around middle of flowering phase.
now it clicked; just late in flower not alot of N is being fed that to the plant that is what cuases the late flowering yellow.... ok thank you