What is the optimal temp and humidity for Veg and Flower?

Let me know what you guys think.:+1:


In veg I keep my room at 65 humidity and flower I try to keep it around 35-40

For temps in veg during Lights on around 78 and lights of around 68. In flower lights on at 75 and lights off around 64. Easier for me to switch up Bc I do veg and flower in different rooms. So I keep the rooms consistent and move the plants.


This VDP chart was provided to me by @imSICKkid and I try to adhere to it. Try to stay in the green shaded area. hope this helps.


Yeah man try to focus on your VPD. That’s where your going to have the best results.


Ya my room is perfect on the outter edge of my garden where I can control the temps and humidity best but I need to circulate the humidity/air better in the center of my tables. Such a difference where the VPD is off, need more gear I have come to find… Next crop will have to do I’m poor as hell ATM…


The top of that VPD chart is missing, which has some important information. It specifies that the values listed in the table are accurate when your leaf temperature is 2°C lower than the air temperature listed on the vertical axis. The full version also has a legend in the top right corner telling you which “colour range” to stay in during what stage of growth.

My fresh clones work their way between a VPD of 0.0 - 0.25 in the first week, then from 0.25 - 0.65 as they continue to root. The temperature and humidity values stay very consistent day to night. These temperature and humidity values fall into the pink zone in the upper left of that table.

In the vegetative phase the plants transition from 0.65 to 1.1 (as high as 1.8 depending on cultivar) over their weeks, with the temperature and humidity day/night differential nearly constant at first and swinging larger as the weeks pass. These values are found in the blue/green values of the table.

In the generative/flowing phase the plants go from 1.1 - 2.0 with day/night differences increasing even more dramatically. These values in the table are yellow/pink.

All the values I listed are for the lights-on VPD target. Lights off values are 0.25 to 1.0 lower that the lights-on level for the given phase, with the larger differences taking place near the end of the generative/flowering phase.

If you’re looking to dial in your grow on a small scale I really like the “Plug’n’Grow” temperature and humidity controllers for their day/night settings, though any controller that allows for day/night settings will do.

As an example:

I’ve got my home grow in mid-veg right now. Target lights-on VPD is 1.0, target lights-off VPD is 0.75. I want to keep my day/night differences fairly small so my controllers are set to:

Day temperature: 27°C
Day humidity: 60%

Night temperature: 25°C
Night humidity: 65%


Tks for the info @devjyarn I like specific use info. I’m looking to buy a controller to run my 20ft x16ft room with 15 1000w (soon,just 9 ATM)hps & MH. Need to run CO2 and negative air so need smart fan controller to be included. And be great if it did CO2 control as well. Do you know of any that are reliable and do everything? I’m also running a hydro fogger (humidifier)

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I like the trolmaster system for doing precision growing in rooms your size, if you intend to keep it as just one growing environment. GrowerMD on YouTube does a nice walkthrough of his room. https://youtu.be/PU3zBvzMy5g

The proper set of controls for a room really depends on your needs, setup and comfort with using the controls. Some of the larger greenhouse automation systems allow you to place conditions on actions, letting the computer decide if it makes more sense to exchange fresh air rather than condition what is already in the grow environment. For example, our summers in the Canadian prairies are very dry, but hot. Systems like Argus and Priva allow you the ability to bring in hot, dry air and cool it by humidifying the room (either mechanically, or with an expected increase in transpiration) if it is more energy efficient than running the room’s cooling system.


Tks I’ll check that out .it is pretty dry here as well I’m usually humidifying my space. But humidity spikes at night.

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I understand. I’m typically adding both heat and humidity in my grow. With the night time humidity spike I would again recommend a controller with a seperate night time humidity set point. However, if your humidity is difficult to dial in, set your night temperature so that the intersection of your night temperature and humidity fall within your desired night time VPD targets.

It’s been valuable to me to stop looking at temperature and humidity separately and begin to consider how they act together to form the Vapor Pressure Deficit. A plant at 30°C and 70%RH is transpiring just as hard as one at 25°C and 60%RH. It lets me grow more efficiently.


Going to watch this thread. My next grow season, dialing in my VPD is one of my goals. I don’t have fancy equipment for it, but what I do have works…if I help it along. Last year, I really started working that VPD for 2 of my grows, but then I kinda slacked off on the 3rd one. I won’t ever do that again!

VPD and pH really affect how your plants access and process their food.


If you’ve got any other questions, feel free to ask here or in a private message. I’m here to share knowledge and gain contacts within the regulated Canadian market and work with established or developing producers.

In regards to pH - keep it rock steady from day to day. A reservoir auto doser and monitor (like the one offered from Bluelab) will remove one of the biggest variables that affect your crop efficiency and yield. However, I do like to work my way down from about 6.3 to 5.8 from propagation to harvest as it can aid in nutrient uptake at a given growth phase.


Thanks! I don’t grow hydro, myself. I grow in a soilless blend, using organic nutrients and lots of microbes. After much tweaking over several grows, I have my system’s pH dialed in very nicely. The VPD is good, too, as long as I do my job.

I don’t use any automation, except for digital timers. I like to keep my little hobbyist grow simple.

I’ll definitely keep an eye on this thread and any others VPD related.


@jonathanruiz here are a few articles about VPD, the way temp and humidity work together to make your plants grow.




I think the green is too narrow, my plants are off the vdc chart some, and it goes against what I was taught, to keep humidity in the low 40’s in the last weeks of flower so you don’t get bud rot mold. It has worked well for me, if I go by that chart, then when my humidity is 40 my temp has to be in mid 60’s ? And if I let my humidity get high like the chart suggests I will most likely get bud rot. So that chart has to pertain the time frame this is most best, past mid flower I thnk bets are off.

The green cells of that chart are not your targets for flower. You want to be in the yellow or pink on the lower right.

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Flower VPD Chart