Late flower humidity control, what actually works outdoors

We're getting into the window where mold kills crops out here in the PNW, so I want to share what's kept me clean through some genuinely wet Septembers. The target I chase is 45-50% RH during lights off, and under 55% during the day. Once you're past week 5 of flower, buds are dense enough that internal moisture becomes the real threat, not just surface dew. I run a cheap wireless hygrometer clipped inside the canopy, not outside it. The ambient reading from a weather station means nothing when your colas are packed together and trapping humid air. That inside-the-canopy number is almost always 5-10 points higher than ambient and that's where botrytis starts. Defoliation timing matters more than people admit. I do a moderate lollipop pass around day 35 of flower specifically to open airflow at the bud sites. Not a heavy strip, just removing leaves that are tucking against developing colas. Moving air is your best tool. A battery powered clip fan aimed up through the canopy on a timer runs overnight for me. Anyways, if you're watching a forecast with three straight days of rain in week 6 or later, that's your cue to harvest early or get serious about coverage. Waiting for full ripeness in a wet year is how you lose the whole plant to rot. A mostly ripe harvest beats a moldy one every time.

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Experienced4d ago

Most of this is solid, but i'd push back a little on the "mostly ripe harvest beats a moldy one" framing because it kinda glosses over how much the terpene profile shifts in those last 10-14 days. That's where a lot of the complex top notes develop. Losing that window isn't just a potency thing, it's where your terps go from good to exceptional. What i've actually found helps is running a portable propane or electric dehumidifier inside whatever shelter i'm using, even a simple poly tunnel setup makes a massive difference in the PNW window. You're not fighting the rain directly, you're just breaking the stagnant humid air around the canopy. Combined with the clip fan approach you mentioned, i've been able to push closer to full ripeness on some really dense phenos that would've rotted otherwise. The inside-canopy hygrometer tip is real though, that's not something enough growers actually do. Ambient readings are basically useless past week 5.