Week 5 yellowing, N deficiency or just natural fade?

Running a soil grow, week 5 of flower, and the lower and middle fan leaves are starting to yellow and drop. Not super dramatic, but noticeable. I mixed my own base nutrients this run, calcium nitrate heavy on the N side early on, then tapered it down around week 3 like i usually do. Now i'm second-guessing that taper. The thing is, some yellowing in late flower is totally normal as the plant pulls mobile nutrients back toward the buds. But week 5 feels a little early to me for that to be the main driver, especially when it's not just the very bottom leaves. It's creeping into the mid-canopy a bit. For those who've seen both, what's your tell? With true N deficiency i'd expect it to move faster and look more uniform, but natural senescence can look pretty similar early on. Do you push a light N top-dress or feed and watch the response, or just leave it and monitor? My water is RO so i'm not leaning on anything from source water to mask the picture.

2 comments

2 Comments

Experienced1d ago

Week 5 mid-canopy yellowing in soil, I've been there and honestly the thing most people skip is checking runoff EC before they do anything else. If your soil is still reasonably charged, pushing more N might just salt up the root zone and complicate your picture later. If runoff EC is dropping fast, that tells you the taper hit harder than the plant wanted. My personal read on true deficiency vs senescence is speed and color quality. Natural fade looks kind of mellow and even, leaves go pale yellow then straw. Deficiency tends to look a little more washed out, sometimes with a slightly greenish-yellow tint that moves noticeably within a few days. If it's creeping mid-canopy and you can almost watch it move, that's usually not just the plant recycling. Given you're on RO with a custom mix, i'd do one light N feed, nothing dramatic, and watch the response over 5-6 days before assuming it's fine. Leaving it if it's actual deficiency in week 5 will cost you in terpene density late. Starved plants in the last few weeks just don't finish the same.

Experienced1d ago

The runoff EC check is solid advice, but five to six days feels long to me when you're already in week five. If it's moving mid-canopy, I'd want a response in two or three days before committing to more N that close to finishing. Slower diagnostic windows make more sense earlier in flower when you have room to course-correct.