What Are The Best Temperature & Humidity Levels For Growing Marijuana?

[Mars Hydro]

Some cannabis strains could survive in suboptimal environments, but they probably won’t thrive. If you want to grow fire indoor flowers, you have to take control of your climate. It’s crucial to monitor the relationship between temperature and humidity as your cannabis plant matures.

From CO2 levels to watering schedules, temp and humidity impact many aspects of your grow operations. Since warm air retains moisture, it can supply crucial hydration to fragile seedlings. However, as plants mature, too much humidity could pose an increased risk of mold.

Average Temperature & Humidity Levels For Cannabis Plants​

Finding the optimal temperature may take a bit of tinkering, but there are a few general heat and humidity levels that cultivators could use as a guide.

Keep It Steamy For Seedlings​

Since cannabis seedlings don’t have a sturdy root structure, they will absorb most of their water through the air. For this reason, cultivators need to ramp up their average humidity during this initial stage of growth.

Most seedlings perform well in an environment with 65 - 75% humidity and temperatures between 68° - 78° F. However, if you’re working with clones rather than seedlings, you should invest in a humidity dome. Young clones need the highest humidity rates of about 75 - 90% for optimal growth.

While seedlings need high humidity rates, cultivators still have to watch out for complications like mold. It’s best to start with the highest humidity rate and gradually decrease as plants approach vegetation.

Also, home-growers that live in a state with cold temperatures should invest in a high-quality Mars Hydro heat mat. These devices help keep your delicate seedlings warm as they begin developing their roots.

Increase Ventilation For The Vegetative Stage​

When cannabis plants transition to the vegetative stage, they don’t need as much water from the atmosphere. In fact, cultivators should begin encouraging their strains to develop a robust root system by watering on the soil around their plants.

To assist this natural transition, it’s best to dial back humidity to the 60 - 45% range. However, you should consider increasing the ambient temperature to mimic the summer season. An optimal temperature range for vegetation is between 70° - 82° F.

High heat is especially significant if you’re adding CO2 to your grow space. Plants need higher average temperatures to use supplemental CO2 for photosynthesis. Depending on how much CO2 you add to your grow space, you could safely raise temps to 85° - 90° F.

Please don’t forget to incorporate a ventilation fan into your cultivation strategy. These fans help strengthen stems and reduce the risk of pests and mildew.

Dehumidify For The Dankest Buds — Temperatures During Flowering​

As strains move into the flowering stage, they should have a fully-developed root system. Therefore, these plants don’t need high humidity for their hydration needs.

In fact, excessive heat will significantly increase the risk of mold and hermaphroditism. If you have a dehumidifier and inline fan, this is the best time to put them to use.

Ideal humidity ranges for flowering plants are about 50 - 30%. Temperatures should decrease throughout flowering to mimic the change from summer to autumn, with average temps between 70° - 80° F.

Heat & Humidity For Cannabis — A Few Final Considerations​

Most cannabis plants perform best in a climate that resembles subtropical regions. Also, every strain needs the highest amount of humidity in the seedling phase, since the plant’s roots are at their weakest during this stage. As the cannabis plant matures, cultivators should keep reducing their room’s total humidity to avoid complications like mildew.

While these temp and humidity guidelines work for most cannabis plants, cultivators must double-check strain-specific guidance. For instance, full-bred sativa strains perform better in areas that mimic regions like Thailand or South America. By contrast, indicas could fare well in grow rooms with slightly lower temperature and humidity levels.

Balancing heat and humidity may not come easily, and the ratios that work for one hybrid may not work for another. Be sure to take detailed notes of average temps and humidity levels to better understand the ideal setting for each strain.

Universal Temperature and Humidity Levels For Indoor Cannabis Growing

Growth stage	Temperature	Humidity
Seeding	68° - 78° F	75-65%
Vegetation	70° - 82° F	60-45%
Flowering	70° - 80° F	50-30%

For better preservation:

If you have a different opinion, say it and let's discuss it.

 

[AdaminCO]

*waiting for someone to pounce*


These are very accurate numbers compared to what I understand too. But is VPD really that big of a deal???

Alot if folks dismiss VPD, I however do not. These are the small things that make the difference in healthy plants.

This is as basic as it gets. Something I ran across awhile back….

“Why is VPD important for plants?​

If VPD is too high, your plants will be transpiring really heavily. This means they'll be absorbing more nutrients, which can cause toxicity.

On the other hand, a very low VPD will also cause problems. Your plants will not transpire, which means they won't be able to uptake fresh nutrients, and they will develop deficiencies.”

“You can manipulate VPD as a grower to encourage your plants to keep their stomata open and constantly expel moisture out into the growing environment.

This results in maximum nutrient uptake through the roots. When your plants transpire, they then need to take up more moisture through their roots to accommodate for this lost moisture.

And when you feed nutrients to the root zone, these get taken up along with the moisture - which is how feeding works.

So in theory, you can manipulate VPD and encourage your plants to constantly take up nutrients. There is a fine line, though, as too many nutrients is not a good thing (toxicity)

But if you can dial in the optimal VPD range, it will results in a more efficient, healthier plant. And thus, a more robust, heavier-yielding plant.

Growers who can successfully dial in their VPD can maximize the genetic potential of their plants.”

 

[Mars Hydro]

Temperature and humidity are defining factors for VPD, sometimes called vapor pressure deficit, which is what truly affects the health of a cannabis plant. Vapor pressure is the pressure at which liquid becomes a vapor. Here is a real-world example of vapor pressure in action: When you boil water on the stove, you heat the water, increasing the pressure to a point at which it reaches the vapor pressure of the atmosphere around it and becomes steam. In cannabis cultivation, VPD refers to the difference between vapor pressure within a plant and the vapor pressure of the air surrounding the plant. VPD is responsible for driving a process in the plant known as transpiration, which directly impacts plant health.

If VPD is too small, peak growth rates are not achieved, and problems like mold or root rot can become an issue. If VPD is too large, the plant stomata will close in an attempt to limit transpiration, which can result in issues like tip burn and leaf curl. VPD can be directly calculated from the temperature and relative humidity (RH) of both the plant and the grow room. Both of these concepts are explained in detail below. The surface temperature of the plant and the dry bulb temperature of the room are approximately the same, but since the plant has water forming, the plant surface will be at 100% RH when it is transpiring. For a given design temperature, we can modulate the VPD by changing the RH of the grow room.

To put it simply: Consistent temperature and relative humidity in the space --> consistent vapor pressure deficit --> plant transpiration --> plant growth.

So the humidity and temperature of the growing environment can control the transpiration of the plants. The grower only needs to keep the relative humidity within reasonable limits to facilitate transpiration and growth.

A VPD range of 0.8–1.1 (kPa) is commonly known as ideal in the vegetative stage, while a VPD range of 1.0–1.5 (kPa) is commonly known as ideal in the flowering stage. Tables I and II show that the same ideal VPD range can be obtained at different temperatures and relative humidities.

 

[Perfect Sun LED]

I would not let my grow room drop to 30% humidity during any stage, but I find this highly unlikely during flower anyway. The plants raise the humidity. If you happened to have a dehumifier that could reduce humidity to 30%, I do not recommend it. 45% for flower, maybe as low as 40%.

 

[nivek]

i am more curious about whom might be writing this than i am about the info.

peace and love from canada,, this is the most comprehensible post i have ever seen from mars hydro,,

karma sent friend

 

[AdaminCO]

Here’s the chart I use.