Getting the right temperature and humidity is important when growing marijuana indoors. Environmental factors definitely contribute to overall yield, as well as quality.
There is actually a broad range of temperature and humidity combinations that will work. But some are definitely better than others. Then there are other tweaks that can be made, such as lowering temps before harvest to bring out color.
What are the best temperatures for growing indoors? That is what we will discuss in this blog article.
Use Different Temperatures for the Vegetative and Flowering Stages
When growing marijuana indoors, you will replicate the two stages of growth, otherwise known as the two photoperiods of cannabis. The first is the vegetative stage, which uses a light cycle of 18 hours on, and 6 hours off. The second stage is called the flowering period, which has equal amounts of light and darkness, or 12 hours on, 12 hours off.
Both of these photoperiods have their own optimal ranges for temperature and humidity.
Best temperatures for Seedlings and Propagation
First, let’s start with propagation. This really only applies if you are engaging in regular cloning, but it can also apply to growing seedlings.
For plants at this stage — basically infancy — we want to baby our babies in the nursery. You want to keep humidity above 70% or so when you have clones in the dome. And the same for using an EZ-Cloner or other means of maintaining clones.
Seedlings, as well, will do best in warm, humid environments. The heat and humidity is actually necessary to get your seed to sprout.
Best temperatures for the Vegetative Stage
During the vegetative stage, the plants undergo their early growth and development from a seedling or clone to a large plant, ready to bloom.
It is best to mimic a tropical environment for this stage, with warmer temps and higher humidity. Your plants are young, and we want to invite them into this world with a warm, humid environment. This combination is great for vegetative growth.
The upper 70’s work great, but if your equipment and/or environment limitations require warmer temps, that is fine too. We recommend that you keep your temperature at around 78 to 80 degrees fahrenheit, and your humidity around 65 % or so.
Anywhere between 75 and 85 degrees fahrenheit works just fine for the vegetative stage. Using those temperatures will give you a humidity range from about 60% to 70%. You can even let temperatures get as high as 90 degrees and above. Just keep an eye on everything. And CO2 helps.
When working with ranges of temperatures and humidity, try to match the two, by keeping humidity a bit higher with warmer your temps. And the lower the temps, the lower the range of humidity.
Temperature and Humidity Ranges for the Flowering Stage
For the flowering stage, we recommend keeping temperatures in the mid-70’s, and humidity between 50-60% RH. Beginner growers will be just fine aiming to keep temperatures at around 75 degrees, and humidity at around 57% or less.
More experienced growers can play around with tapering up and down. We have another article that covers more advanced approaches to flowering stage temperatures. If you are hungry to improve your game and take on some new challenges, we definitely recommend checking out that article.
You can grow cannabis indoors using a broad range of temperatures and humidity
It’s important to remember that cannabis is an extremely hardy plant, capable of enduring a lot of stress. That’s why they call it weed, after all. Your cannabis plant is not a fragile snowflake that requires a safe space in order to survive.
For example, you can grow weed in extremely hot environments, over 90 degrees F. And you can also grow weed in cooler temperatures, such as the lower 60’s (fahrenheit). Neither of these is optimal. But there are also things you do can in both of those situations to mitigate the suboptimal circumstances, should you find yourself forced into one of those situations.
Extremely high temperatures during the Flowering Stage
Take for instance extremely high temps. When temperatures are higher, you need to bring up your humidity to accommodate the heat. When you get above 90 degrees, you also need a lot of CO2. High temperatures will cause more evaporation which will help with the need to increase humidity, but will also require that you water more frequently. You must keep things moist.
Unfortunately, all the excess moisture and humidity create an environment that encourages growth of mold and mildew, so you will have to really monitor your plants for these issues.
Flowering cannabis in colder temperatures negatively affects yield
On the opposite end of the spectrum is low temperatures. Here, you will want to keep the room extremely dry, even under 50% Relative Humidity. This is not ideal for yield. In fact, this is terrible, as your plants will be stressed, and will not bloom into giant blossoming ganja plants with huge colas. However, you may see some wicked color expression. And possibly some other unique traits. But you will definitely not achieve much in the way of yield.
Your biggest struggle in cold temps will be keeping the humidity down. If you don’t, you have literally the worst environment possible for mold and mildew: cold and wet. But if you can keep it dry in there, you will make it out alive.
Cannabis is amenable to different conditions, but top shelf quality requires optimization
As stated, cannabis is hardy and you can grow it in a pretty wide range of temperature and humidity combinations.
However, when it comes to growing the very best weed, the details do start to matter. It’s easy to grow “mids” but achieving all around top quality requires a greater attention to details. And when you are trying to maximize yield output, you must dial this stuff in.
As always, happy growing 😉