Late flower humidity targets before the rains hit

If you are pushing into September outdoors and your buds are stacking up, this is the window where mold wins or you do. The target i shoot for is 45 to 50 percent RH during the day and no higher than 55 at night. Once you get above 60 consistently, especially with dense canopy and cool nights, botrytis is basically waiting for an invitation. Airflow is doing more work than most people give it credit for at this stage. I run two oscillating fans on a timer in my greenhouse from dusk to midnight, which is when temps drop and moisture climbs. Outside plants i will actually hand-strip some of the larger fan leaves around the bud sites around week six of flower just to open things up. Feels wrong but it pays off. Get yourself a decent hygrometer with a min/max log. The overnight low RH reading will tell you a lot. If you are waking up to 70 percent or higher, you need to either harvest earlier than planned or get some airflow on those plants at night. Anyways, a ten dollar thermometer sitting on a stake in the middle of your canopy is worth more than most products being sold for mold prevention. Short-season strains help enormously here. Running something that finishes late September instead of mid October has saved me more than once when October rain came early. Know your local first frost and first heavy rain dates and count backward. That math matters more than anything else this time of year.

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Experienced3d ago

The fan leaf stripping point is something people sleep on. I was resistant to it for years because late flower defoliation always felt like I was robbing myself of photosynthesis right when the plant needs it most, but the botrytis I lost a whole Zkittlez pheno to in 2021 changed my thinking fast. Open canopy beats marginal sugar production at that stage, full stop. The one thing I'd add is that terpene development can actually shift in that 45 to 55 RH window, not always for the worse either. I've noticed some of my fruitier phenos get a sharper, more concentrated smell in the final two weeks when conditions are drier and slightly stressful. Whether that's the reduced humidity or the cooler nights I can't say for certain, but the correlation keeps showing up in my grows. The short-season strain point is the real move though. People spend so much energy on environmental control when the easier answer is just running genetics that match your climate. Chasing a 10 week outdoor photo into mid October in a wet region is borrowing trouble.