Controlling the environment around your plants is an integral part of growing indoors. Though some factors can be difficult to get a handle on, it is important to understand what the optimum conditions for growing marijuana indoors are. That way, you can start making a plan about how you want to tackle these particular issues.
Marijuana thrives in temperatures ranging from 60-80 degrees F. Keeping your grow room within this range is the best way to ensure that your yields are maximized. It is a good idea to lower the temperature at night if possible. This practice isn’t absolutely necessary, but it is widely suggested since it better emulates a natural setting (it gets cooler at night).
I keep my grow room around 70-72 degrees during the day and around 60 degrees at night. I control this very simply by keeping a space heater within the grow room and changing the settings when I wake up and before I go to bed. Eventually I would like an automated set up for temperature, but I haven’t yet implemented that.
As with other components I discuss like water level and lighting cycles, stability goes a long way. Temperature is no different. Marijuana is extremely resilient, so a scorching day or frigid night isn’t going to kill your plants. If these variances happen regularly though, it will start to add up and damage your final yields.
Warming Your Grow Room
Use a space heater with easily adjustable temperature settings to keep your room warm. Because I like to keep my nutrient solution cool to help prevent root rot and warm air rises, I like to elevate my space heater closer to the plants and away from the tank .
I use a thermometer to measure the tops of my plants since that will be the hottest temperature my plants are exposed to. I aim for 70-75 degrees F at the marijuana tops which usually means 65-70 degrees F around the base depending on the height of my plants.
Cooling Your Grow Room
The most common way to cool a room is with proper air circulation. By forcing warm air out with fans, there is an opportunity for it to be replaced by cooler air thus decreasing the room temperature. For this to be effective though, you need to be able to draw cooler air from somewhere else.
I didn’t really have an effective way to accomplish this, so I bought an AC unit for the window right outside my grow closet. Coincidentally, this is the computer room, which I spend the most time in, and it was sweltering on hot summer days, so it just made sense to buy the unit for both me and the plants. I adjusted the temperature of the computer room to such a temperature that I could close the door of my growing closet and still maintain the optimal temperature inside.
Not everyone is going to be able or want to use a solution like this, so you might have to be creative to think of ways to keep your room cool if necessary, otherwise you may be stuck only growing in winter when temperatures are lower.
Keep the season in mind. For instance, during winter in an HID setup, the lighting system may provide all the heat your grow room needs. It does for mine. However, during the summer, the room becomes too hot without some kind of cooling.
Humidity is a measure of the amount of water in the air at any given time. Relative humidity (RH) is a measure of the amount of water in the air compared to the maximum amount that could be held at the given temperature. RH is represented as a percentage anywhere from 0-100%.
RH is an important consideration because if it is too low, your plants will use a lot of energy to expel water out of its system. If it is too high, there will be a lot of moisture in the air which can lead to mold and literally wipe out your end yields.
The Relative Humidity range you want is between 40-60% for vegetative growth and 30-50% for flowering. This range will ensure that your plants have an environment to grow efficiently without expending too much energy and without being invaded by mold.
Like temperature, one effective way to help keep humidity under control is by having constant air circulation. This is especially helpful in preventing the development of molds.
Another relatively easy way to control humidity is by raising and lowering temperatures in your grow room. When you lower the temperature, less water can be held in the air meaning RH goes up. Raising the temperature means the air can hold more water vapor and RH will go down. Both of these assume that changes in temperature have no effect on the amount of water in the air (which they likely will), so keep a watchful eye when using this method.
If you are having trouble even with proper circulation and temperature changes, you may want to consider a humidifier if the humidity is too low or a dehumidifier if the humidity is too high. These tend to be used more in heavy duty grows, but if you have the resources, there is nothing wrong with beefing up your grow system with one of these devices.
Why Air Circulation Matters
A grow room that has proper air circulation provides a positive environment for your plants to grow. As I have already touched on, strong air flow helps to control room temperature and humidity levels.
However, it has one additional benefit and that is air flow strengthens marijuana stalks. By pointing a light breeze in your plants’ direction, it forces the stalk to become strong, hardy, and increases overall toughness.
Many growers claim that stronger stalks and branches lead to better bud yields. I can’t verify that for sure, but I can tell you that it is a lot easier to manage a plant that can take some rough housing and isn’t a whimpering nancy.
Setting Up Circulation
When you begin to tackle an air circulation setup, you need to establish a couple of things.
- Size of Room – Do this by multiplying the width x length x height of the room. For instance, my grow closet is 2’ (Width) x 2’ (Length) x 6’ (Height) meaning I have 24 cubic feet of space in my closet.
- Rate of Change – This indicates how often you want the air in the room to be replaced. The standard I often see is 1 entire room air change per minute, but some people go for a room change every 3-5 minutes. The hotter your grow room gets, the more circulation you will want to get that hot air out.
Once you know the size of the room and how many changes you want per minute, you can figure out what kind of fans you will need. In the case given:
24 (cubic feet of my room) x 1 (number of room changes per minute) = 24 CFM
So if I wanted a fan that would give me 1 room change per minute, I would need a fan that could move at least 24 CFM (cubic feet per minute). Pretty straightforward, right?
For best results in your air circulation setup, you will need 1 fan blowing air out and 1 blowing air in. This is especially true as a grow room gets larger.
If you can only afford 1 fan and your room is small, you can use a passive intake as well, which is what I use. A passive intake is just a hole in the room closer to the floor where air can travel into your grow room. Using the 1 fan to blow air out will force your grow room to have lower pressure, which causes air from outside to be sucked in through the passive intake. It’s not as effective as having a second fan, but it will do the job if your room is small.
The last thing you will need for a good air circulation setup is ducting. Ducting will allow you to transfer the expelled air away from your grow room such as into another room. It will also allow you to pull in fresh air from another place such as outside. Ducting gives you a lot of adaptability in putting together a setup that will fit your needs and can be purchased at a reasonable price.
- Determine what actions you are going to take to moderate temperature in humidity. If your house tends to be cold, you might only need a small space heater. If your house is on the hotter side, you will want to look into setting up a proper airflow system.
- If you decide that air circulation is going to be an absolute necessity for you, begin thinking about how you will install the fans and ducting. Where will you get air from? Where will you exhaust air to?
- Get a full understanding of your plants environmental conditions. You are in complete control of the area your plant grows. If you want your plants to be good to you and give you hoards of tasty buds, you must be just as good to them.