VPD

Both. Going over 65% should be avoided. Extremely low or high VPD should be avoided. What you need to do is get your temperatures down. Consider lights-on at night and dark cycle during the day. Exhausting outside is also an option that may or may not be enough on its own. Grow during cold season, which is what i do. Slim down garden - less light = less heat... all sorts of options including an AC unit, which will also reduce humidity. An RH% above 65% invites microbial growth. You should also avoid extreme VPD values - low or high. This will cause slow growth. 88F is extreme. Thisi s the root of your problem. Fix that and the rest will fall in line.

Yo, at this stage in flower, you don’t wanna be sittin’ at 50–60% RH that’s too humid, especially with high temps. You really wanna dial it into the 40–50% RH range to keep your VPD in check and avoid bud rot. Late flower is all about drying it out just enough so your buds finish dense and clean. At 88°F, 60% RH throws your VPD off and slows everything down. Either drop the temp a bit or lower the humidity whatever gets you closer to that 1.2–1.5 kPa sweet spot. That’s the zone where your plants breathe right and stack weight without risking mold. So nah, don’t shoot for 50–60%, stay closer to 40–50% and you’ll finish with dank, tight buds.👊

Vpd, vapor (water) pressure deficit (difference) between two atmospheres. The more optimal vpd the more efficient the plant will drive transpiration, transpiration drives osmosis which creates turgor. High turgor, high cell elongation, high stress, high workload. Vpd is about rapid growth. Last week or two of ripening is not about rapid growth, I always find terpene profile is at its highest probably 2 weeks prior to trichomes being ready, but that's just my opinion. Last week or two should be lowering rh to ensure a safe finish, high temps come with high humidity, still pushing 85f for last two weeks you will be lucky to have any profile whatsoever. As buds get bigger they become thick, moisture can easily get trapped in 50+rh bringing with it botyris( bud rot) Terpenes start to degrade around 68f and above. It's about finding a balance, any time I tried to push growth hard for last weeks all I end up doing was burning off smell and taste and promoting early CBN production in buds. Buds will be airy the more heat they are exposed to. cannabis buds can be affected by cold temperatures and can experience compression, not going to change drastically but the difference was noticeable. Good luck 👍

You are essentially asking: (1) is my function of temperature and dew point or (2) is my function of temperature and [temperature and dew point] more important? Know how these play together and the answer is clear. At the end of the day one is a ratio and the other is an absolute difference (VPD). VPD is the more informative measurement.

In my opinion, VPD is more important than simply keeping humidity within a certain range. Humidity should always be considered in relation to temperature, because only the combination of both gives a realistic picture of the plant’s environment. That’s why I believe VPD is the more critical factor. However, your top priority should be lowering the temperature. 88 °F (which is about 31 °C) is definitely too high. I strongly recommend keeping it at a maximum of 28 °C, which is roughly 82 °F. Hope i can help you. Keep growing and lower your temp.

Honestly, if your temps are hitting 88°F, it's more important to focus on staying in the right VPD zone rather than just trying to keep RH in the 60s. At that temp, 60% RH actually puts your VPD too low, which can slow down transpiration and nutrient uptake — not ideal, especially in flower. You’re better off adjusting your RH to match your temperature and keep VPD around 1.2 to 1.5 kPa during mid to late flower. That usually means aiming for around 50–55% RH at 88°F. It helps your plants “breathe” properly and can really make a difference in overall health and resin production.

Hey Growmie, If your temps are hitting 88°F, focusing on your VPD is more important than sticking to a fixed RH like 60%. At that temperature, 60% RH gives you a pretty high VPD, which can stress your plants and slow down growth. You'd want RH closer to 70–75% in veg to keep VPD in the ideal range. During flower, 60–65% RH can work, but only if you’ve got solid airflow to prevent mold. Bottom line: don’t chase a specific RH number, dial in your VPD for healthier, happier plants.