Growing Marijuana Guide – Indoor Grow Room Basics

Get your hard hat on! It is time for a marijuana grow room. 

Get your hard hat on! It is time for a marijuana grow room. Growing Marijuana Guide – Indoor Grow Room BasicsGrowing Marijuana Guide - Indoor Grow Room Basics

Building your grow room will probably the most physically exhaustive part of growing your own marijuana indoors. The room can be anything from a bedroom closet to a home-built grow box. There are a couple of things to take into consideration when choosing a grow space.

Grow Tools.

The indispensable tools for indoor cultivation are all those things that allow us to maintain stable and optimal parameters: lamps, reflective materials, extractor, thermometer, hygrometer, fans, nets, and support tools.

EC and PH meters, timers, extensions, and pruning shears. Among the tools not necessary to grow plants, but often necessary for our safety, we include the activated carbon filter, which has the function of making our secret garden as “stealth” as possible, preventing the scent of our buds from reaching “unwelcome” noses.

Among the non-essentials (because they are only necessary in certain cases) we have heaters, air conditioners, humidifiers, and dehumidifiers. If we have chosen an ideal location, we will not need it in most cases.

Grow Lights.

The grow lamps are of fundamental importance, as cannabis is a big lover of light and it is, therefore, its important to provide it with enough and of the right intensity.

There are several lighting systems, from the old but always effective HPS, up to the new and high-performance LED quantum boards, passing through neon, CFL, CMH, MH, LEC, plasma …

The thermomometer/hygrometer is used to monitor that temperature and humidity are optimal, a digital model, with probe and memory, will do its job very well for years at a modest expense.

EC and PH.

Cheap PH test kit
Cheap PH test kit

The EC and PH meters are taken lightly and considered unnecessary by some growers … The same growers who then contact me because they cannot understand why their plants are suddenly turning yellow and looking less than healthy!    Having a correct PH means making sure that plants can properly absorb all the elements.

Bluelab E.C. Truncheon

Bluelab E.C. Truncheon

Bluelab E.C. TruncheonThe EC, on the other hand, allows us to verify that the nutrients we are supplying are correct, avoiding dangerous overfert or deficiencies.


oscillating fan
oscillating fan

Using one or more fans (preferably oscillating) is important as, in addition to ensuring internal movement of air, it stimulates the plants to grow stronger. Beware though! If too powerful it could create wind burns and stress our plants! The wind has to caress the leaves and make the stems sway slightly, dont create a tornado!


Marijuana likes temperatures between 70 and 85 degrees

Marijuana likes temperatures between 70 and 85 degrees

Temperature: The temperature of the grow room should not be excessively cold or hot. Marijuana likes temperatures between 70 and 85 degrees. Keep in mind that the lights will raise the temperature. If you want to grow in a space that cannot provide temperatures within this range, you will need to bring in heaters or air conditioners which can be hard for a first-time grow.


Marijuana likes around 40-60% humidity
Marijuana likes around 40-60% humidity

Humidity: The room should not be excessively damp or dry. Marijuana likes around 40-60% humidity, so make sure you can maintain the humidity in this range. You may use a humidifier or a dehumidifier if necessary.


Light The grow room should be isolated from external light sources.
Light The grow room should be isolated from external light sources.

Light: The grow room should be isolated from external light sources. Light leaking out of the room can tip people off that something is going on and if you are trying to hide your garden from somebody, this is a dead giveaway.

More importantly, though, the plants need to have as minimal light as possible during their lights-off phases. Cardboard and duct tape are a great way to seal light leaks.


Size: The location you choose will need to be high enough to support an adult plant (depends on strain) and will need to have enough surface area to support however many plants you choose to grow.


Location: Location is very important. You don’t want the plants in high traffic areas where they might be spotted or people may interfere with their optimal growth. You also don’t want to plant somewhere next to electrical equipment or heating systems. If you need to get repairs done, the repairman might spot your crop.

Build Your Grow Room.

cannabis growroom_layout

Once you’ve found a suitable location to build your grow room, it’s time to start building. The first task is to work on your circulation. For small operations (1-3 cannabis plants) circulation can simply be opening the door to look at your plants every day, but having good circulation is important to maintain temperature and humidity.

Also, plants exude waste materials through their leaves and if this accumulates, it can be bad for the plants. A good source of circulation is a simple CPU fan connected to an AC adapter.

extractor fan and carbon filter installation
extractor fan and carbon filter installation

The extractor is very important in grow boxes as it allows to perform a triple function: the introduction of new air (and therefore oxygen and CO2) and control humidity and temperature.

It also generates a “negative” pressure which favors the development of plants. There are many extractors on the market, but remember the golden rule: those who spend more spend less, buy quality products because there is nothing worse than having to change something at the wrong time.

The extractors differ in type,  but the most important factor is the flow rate, expressed in cubic meters. Providing “fresh” air will prevent the formation of stagnant air than humidity, making it more difficult for molds, pathogens to proliferate and making life less easy for some parasites.

We need at least 70 changes every hour to bring the right amount of air, so we have to calculate the cubic meters of our grow area or tent and multiply them by 70 to get the flow rate of our ideal extractor.

What Size Extractor?.

For example, for a grow box of 1x1mt and 2mt high, we will do 1x1x2 and we get 2m³ which multiplied by 70 makes 140m³ and that must be the minimum flow rate of our extractor. For 80x80x180cm we will have 1.15m³ and therefore an 81m³ extractor will suffice.

In addition to the size, you must also evaluate the silence (on some models it is expressed in dB), it is not ideal to have the noise of an airplane in your bedroom! Buying one that is twice as powerful and running it at half power might be a good solution to reduce noise. It is important to use quality connection pipes, to ensure the durability and absence of light contamination. I recommend placing an insect net in the inlet and outlet pipes.

Reflective Wall Coverings.

mylar for cannabis growroom
mylar for cannabis grow room

Next, you’ll want to do is cover the walls with some reflective material. This can be as simple as painting the walls white, but for maximum reflectivity, I recommend using Mylar wall-covering. Mylar is available relatively inexpensively at any grow supply store.

This should be placed on the walls smoothly and as completely as possible. Duct tape works for adhering it to the walls.

Then you will want to have some kind of platform to hold your lights. This can simply be a board holding CFL’s in clamps, any number of fluorescent tubes, or an MH/HPS ballast. The platform should be of adjustable height to accommodate the growing marijuana plants. I recommend using a chain connected to the ceiling so that it can simply be hoisted up as the plants grow. Make sure whatever you

I recommend using a chain connected to the ceiling so that it can simply be hoisted up as the plants grow. Make sure whatever you attach the lights to can hold the weight of the potentially heavy lights. Connect the lights to an automated timer that will control the light cycles.


The timer will serve us to provide the right hours of light and dark. 18/6 for veg growth and 12/12 for the flowering phase. Connected to the extractor, however, it can be used to program the air intake cycles. Connected to a heating source (heating rods, heater, etc) it can help us to have correct temperatures.

A good analog timer costs very little and is more than enough for most installations. Regarding electrical wiring, it is important to understand that it is not something where you should make savings.

Electricity is no joke and too often we read news of grow tents and houses set on fire due to underpowered or badly made electrical systems. This doesn’t have to happen! Use only cables of the adequate size, eliminate any stripped cable or damaged sockets and buy quality material with the appropriate certifications.

So, in addition to placing the grow box as close as possible to the power outlet, check the wattage written on the outlet and make sure it is sufficient for the range of your full load grow. If using extensions make sure they are of the right length (avoid coiling or bending of the cable) and end with a power strip that also has fused sockets. Avoid sockets or timers with illuminated switches as they can cause stress in the dark hours.

You are now basically done. The final task is to ensure the area is sealed in terms of light. It might be beneficial to place some kind of plastic surface on the bottom to avoid water damage. The way you build your grow room is up to you, but this guide should help a little. Be creative and have fun, you’ll be spending a lot of time here. Now you can germinate your seeds, or learn how to avoid damaging pests in your marijuana grow.

This guide assumes you are only going to have one grow area. If you are planning on operating a larger grow operation in which you would like to be harvesting as often as possible, you may want to consider have two separate areas or two separate grow rooms altogether, one for the Vegetative Stage and the other for the Flowering Stage.

Checkout the next part of the series  Growing Marijuana Guide Difference Between Male And Female Cannabis Flowers


  1. Hello eddan
    When standard photoperiod cannabis is in the growing stage (before flowering) the plants are best grown under 18 hours of daylight and 6 hours dark.
    When you decide to flower the ideal flowering time is 12 hours of darkness and 12 hours of light. This light cycle gives the plant the maximum light for growing large buds. Some growers use 13 hours of darkness and 11 hours of light to slightly speed up the amount of time a plant will take to harvest. But bear in mind every time you reduce the light period below 12 hours it reduces your final yield of buds.
    If you were to grow using a light schedule of 7 hours of light and 17 hours of darkness you would reduce your final harvest greatly.
    I hope I have answered your question
    here is a link to a post on the flowering stage: https://bestseedbank.com/growing-marijuana-guide-flowering-stage/

    good luck

  2. just simple question —
    How I know , maybe I am wrong, but how I know , cannabis needs minimum five hours of light on flowers time. So my question is — if I put seven on light and the rest on dark for flowering stage — what really happening !!!??? Please take my question seriously and answer exactly . Thanks.

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