Late flower humidity targets that actually matter

Getting into the last two to three weeks of flower and your buds are swelling up nicely, this is exactly when PNW weather wants to kill everything you worked for. Nights are getting cooler, dew points rise, and dense colas trap moisture for hours. This is when botrytis starts and you usually don't see it until it's already spread. The number I chase is 45% RH during lights-off hours, or in outdoor terms, from sundown to about two hours after sunrise when temps climb back up. If you're consistently sitting at 55% or higher overnight in late flower, you're rolling dice. I use a cheap Govee sensor zip-tied right in the canopy, not hanging off a branch outside it. Airflow is the other half. I run oscillating fans on a timer that kicks on at dusk and runs until mid-morning. The goal is to stop moisture from sitting on bud surfaces. Doesn't have to be a wind tunnel, just enough movement that leaves are gently shaking. Anyways, if you're running a full-season strain outdoors in the PNW and you're not doing some version of this by week six of flower, check your dense sites daily. Armpits of branches, anywhere two colas are touching. Catch it early and you can still save most of the plant. Miss it by three days and you're cutting a lot more than you planned.

2 comments

2 Comments

Seedling1d ago

I’ve been running some The Seed Pharm autos the last couple seasons and they finish fast enough that I can usually beat the worst of the fall rains, but for full season photos I’m definitely stealing your Govee in the canopy trick this year. If you’re still looking to add more genetics for next round, they’ve got the BOGOAUTO code running right now which makes grabbing a few extra packs pretty painless

Expert Grower1d ago

The humidity targets are solid, no argument there. What I'd add from my own experience is that the soil surface itself contributes more than people realize. A wet topsoil in late flower is offgassing moisture upward through the canopy all night long. I stopped heavy watering within about five days of the end and let the medium dry down significantly, and my overnight RH in the canopy dropped a few points without touching my fan schedule. The other thing I'd push back on slightly is the "check daily" advice -- by the time you see botrytis visually, you're already behind. Run your fingers gently into the dense sites every other day and feel for soft spots. Your fingertips will catch it before your eyes do, almost every time. I caught a pocket in a thick Kush cola last September that looked perfectly fine on the outside.