87° and 54%? That's very harsh conditions for cannabis.
VPD is a very good way to express combinations of temperature and humidity.
This page is a good explanation of VPD.
VPD is akin to "feels like" for humans. At 87 and 51, your plants are functioning in a desert-like environment.
In veg, cannabis grows best when VPD is 1.0 while VPD in flower should range from 1.2 to 1.5 ( prefer 1.2 or 1.3). Check the intersection of 87 and 54 and your plant is working in a VPD of 1.7±.
To function in a hot and dry environment like that, your plants have to throw off a significant amount of water. Like humans, plants can be described as "bags of water" and when the air is hot and dry, water will flow from that a bag of water to the outside air. That's because there's not a lot of water in the air but there is a lot of water in the plant <== that means that the "deficit" is high and, in nature, everything tends to move from high to low.
With all that water leaving the plant, the roots have to take up a lot more water than normal and when plants take up a lot more water than normal they also take up a lot more nutrients than normal.
In terms of VPD, your plants will do better growing in an environment that is about 10° lower.
The other reason to lower the temperature is that at 87° you're "decimating" your cannabinoids The word "decimate" is a paraphrase of how the loss of cannabinoids was described when temperature of the flower tops of cannabis plants exceeds 78°.
Mitch Westmoreland, a cannabis researched studying under Bruce Bugbee, did a video on growing hemp about three years ago and he mentioned that…
[searches for notes and finds them]
I've grown my plants in the low to mid 80's and, while some of the yields have been prodigious, they haven't had the kick that I associated with premium bud that I've bought from resellers here in CA. In response to the Westmoreland videos, I'm changing my growing processes and am replacing my flower light so I can provide my plants with 1100µmol± as well as keeping the tops of the flowers <78° in flower.
Below are the notes I took on the Westmoreland video on hemp.
Does Hemp Need Extra Water and Fertilizer?
Mitch Westmoreland
Plants grown at 73 and 84 degrees. Plants at 84 were taller but colas were smaller in girth.
At 84 little but taller, a bit more vegetative biomass. Yield wasn't all that affected by the increase tempearature. At 84°, cannabanoids were roughly 1/2 of what they were at cooler temperatures.
Suggest that the optimum is between 70 and 80.
Fertilizer
You've probably come across hundreds of companies promising to boost yield. They "lack a theoretical basis" and you'll probably end up just throwing away money and excess nutrients that will end up polluting our nice rivers.
We recomend that you fertilize it just as you would tomatoes. This is a good comparison there's nothing particularly special about hemp.
One of the big claims that you'll see coming out out of the cannabis industry is that high phosphorus will increase yield and will increase cannabanoid content. We've tested this.
We look at a range of phosporus treatments ranging from borderline deficient to excessive. We found no significan difference, especially as we move toward the rates recommended by the cannabis industry. This has implications because phosporhus is a potent pollutant in our environment.
What we're trying to do is get growers to use as little P as we can while still getting a good crop.
Drought stress
In veg - they're very resiliant. Got to the point where they were severely wilted. They recovered so that it seems as if nothing happened. Hard to see which one's were stressed and while ones were well watered.
In flower - yellowing and dropping of leaves and reduction in yield. CBD and THC does not make production increase.
Temperature - yield increased slightly. CBD and THC plummeted - "cut in half basically". We don't have a good explanation for this right now. We're going to ssee if we can reproduce this and see if we can come up with an explanation for what's going on."
Per my notes, above, high temps will result in a signficant loss of THC and CBD (he doesn't mention terpenes here). Westmoreland continued his research in this area and, in early 2024, released two videos in which he discussed some of the aspect of the work that he had presented for his PhD thesis.
This graphic, the growth rate which is substantiated in other published research, it why I recommend keeping light levels as high as the plant will tolerate. Other research shows that the result is not quite linear but the research indicates a direct cause/effect relationship between increased light levels and crop yield, assuming that light is the limiting factor.
My advice, read up on VPD (you need an IR thermometer to get your leaf surface temperature), drop your tent temp and LST, and adjust your RH so that your VPD is 1.2. That won't bring back the dead tissue in the leaves but it will deduce the very high transpiration rates and that will help resolve the nutrient issue that you're looking at