VPD Adjustment

This time, I plan to use a VPD chart during the growth process.

As a proof of concept (POC), I set up a Raspberry Pi with DHT22 sensors to read temperature and humidity data. Based on this data, I calculate the VPD (air). Additionally, I use two adjusted parameters: VPD (leaf) at -2°C and +2°C compared to the current air temperature.

The application exposes metrics and calculated values, which are collected by Prometheus and displayed on a Grafana dashboard.

On the dashboard, there are data/graphs for three growth stages, along with a calculation of how much humidity needs to be adjusted in the given situation (based on VPD air, leaf -2, and leaf +2).

How well this works in practice remains to be seen. However, this is definitely the fastest way to determine if you're on the right track when following the VPD chart.

This is how my dashboard looks like:

Look at this, if you have the money to spend it could be a game changer,


They're designed to integrate with their controller to control light intensity as the leaf overheats, but I'm sure someone with your tech savvy could have it control other parameters like air temp/co2/humidity

I can not see prices but those gadgeds are usually expensive.
I have a plan (not sure when) to integrate IR temp sensor for leaf, there are quite cheap options (mlx90614 or mlx90615 temperature sensor with various lens addons (extending the range of sensor)).

sebs999 said:

I can not see prices but those gadgeds are usually expensive.
I have a plan (not sure when) to integrate IR temp sensor for leaf, there are quite cheap options (mlx90614 or mlx90615 temperature sensor with various lens addons (extending the range of sensor)).

Click to expand...

I think it's a couple hundered British pounds, I'm not sure exactly how it works but it takes an average canopy temperature, most I've seen only measure a single fixed point.

Even planes have a simpler interface lol
You don't need to follow VPD so tightly, you just need to remember these basic rules
At any given time, veg or flowering:
High Temps - High RH
Low Temps - Low RH
Good luck

DanKiller said:

Even planes have a simpler interface lol
You don't need to follow VPD so tightly, you just need to remember these basic rules
At any given time, veg or flowering:
High Temps - High RH
Low Temps - Low RH
Good luck

Click to expand...

of course we all know basic rules, I have been growing inside for ~20 years, but there was a lot of studies regarding VPD and why not try to achive maximum potencial for them.

The margins between being exactly on the VPD number or in the range of that number is so small, it's really going after the 2-3% difference if any.

DanKiller said:

The margins between being exactly on the VPD number or in the range of that number is so small, it's really going after the 2-3% difference if any.

Click to expand...

There are a bunch of different things we can control to give us 2-3% increases in whatever, when we add them all up it might be a 15% increase overall, that's huge.

DanKiller said:

The margins between being exactly on the VPD number or in the range of that number is so small, it's really going after the 2-3% difference if any.

Click to expand...

That sounds about right.

The primary issue with VPD is to ensure that the grow environment is conducive to a transpiration rate that matches the concentration of nutrients. Of course, if you're in flower and VPD is 0.8, you're asking for problems but there's no particular reason to not let VPD go higher as long as nutrient concentration isn't so high that the increased transpiration rate causes nutrient issues.

I've growing with VPD since I started growing (only three years now) and keeping VPD in range is a good way turn another variable in the growing equation into a constant but, by far, the biggest issue that I see in grow journals is that growers do not give their plants max light. That's what I see here on RIU and on another site that I frequent.

A few years ago, growers were obsessed with finding the magic nutrient mix. Many growers can't grok the idea that it's all the same 16± chemicals, just some ferts come in bottles with pretty labels while some come in big plastic bags. Fert obsession seems to be fading and growers are getting their heads around VPD (AC Infinity stockholders are smiling) but VPD really is just keeping things between the guard rails.

The action is in getting plants to their light saturation point. Putting aside adding CO2, I haven't found any research shows that any part of the grow environment has such a dramatic impact on yield as "lotsa light".

If you scour the pulsegrow.com site, you'll see that keeping VPD on target may improve yield by 20%. There's no discussion, just that assertion and my takeaway is that the 20% is the difference between a truly horrendous VPD and using 0.8, 1.0, and then 1.2-1.5. Plants just don't get wild and crazy if VPD is 1.2 vs, say, 1.6.

On the other hand, research is very clearly that more light = more weed.

Mitch Westmoreland, PhD student under Bugbee, has brought the yield estimate formula up to date in his YT videos that he dropped last year. Instead of it being based on the wattage of your HPS light, his research estimates yield as being 0.2 to 0.3 gm of flower for each mol/sq meter for the grow over the life of the grow.

No other metric in the grow environment is that quantifiable or that large, again with the exception of adding CO2.

"I don't mean to get off on a rant here but…"

Dr. B did an interesting short on VPD:

Delps8 said:

That sounds about right.

The primary issue with VPD is to ensure that the grow environment is conducive to a transpiration rate that matches the concentration of nutrients. Of course, if you're in flower and VPD is 0.8, you're asking for problems but there's no particular reason to not let VPD go higher as long as nutrient concentration isn't so high that the increased transpiration rate causes nutrient issues.

I've growing with VPD since I started growing (only three years now) and keeping VPD in range is a good way turn another variable in the growing equation into a constant but, by far, the biggest issue that I see in grow journals is that growers do not give their plants max light. That's what I see here on RIU and on another site that I frequent.

A few years ago, growers were obsessed with finding the magic nutrient mix. Many growers can't grok the idea that it's all the same 16± chemicals, just some ferts come in bottles with pretty labels while some come in big plastic bags. Fert obsession seems to be fading and growers are getting their heads around VPD (AC Infinity stockholders are smiling) but VPD really is just keeping things between the guard rails.

The action is in getting plants to their light saturation point. Putting aside adding CO2, I haven't found any research shows that any part of the grow environment has such a dramatic impact on yield as "lotsa light".

If you scour the pulsegrow.com site, you'll see that keeping VPD on target may improve yield by 20%. There's no discussion, just that assertion and my takeaway is that the 20% is the difference between a truly horrendous VPD and using 0.8, 1.0, and then 1.2-1.5. Plants just don't get wild and crazy if VPD is 1.2 vs, say, 1.6.

On the other hand, research is very clearly that more light = more weed.

Mitch Westmoreland, PhD student under Bugbee, has brought the yield estimate formula up to date in his YT videos that he dropped last year. Instead of it being based on the wattage of your HPS light, his research estimates yield as being 0.2 to 0.3 gm of flower for each mol/sq meter for the grow over the life of the grow.

No other metric in the grow environment is that quantifiable or that large, again with the exception of adding CO2.

"I don't mean to get off on a rant here but…"

Dr. B did an interesting short on VPD:

Click to expand...

I agree 100%, very well said