Building an indoor grow room

So you’ve decided to make growing cannabis your new hobby? Be warned: the art of growing weed can be more addictive than merely smoking marijuana! Still, with a little fore-thought and the Growers Guide to Cannabis, you can make the indoor grow room a beautiful area of marijuana buds.

Why can’t I just grow cannabis in a corner of my bedroom?

Well you could, ..but it wouldn’t be a very good idea. The idea of building an indoor grow room is to create a controlled environment in which to give your marijuana plants the best conditions in which to grow, and flower. (see The Beginners Guide to Cannabis for an overview of this). In order to do this you need to provide all the elements listed here within a defined space. Before you set up, think about all of the following:

Growing cannabis indoors

Size of Grow

Obviously this will effect the size needed for the grow room. If you are planning to grow marijuana to cover the needs of several medical marijuana patients (ah-hem) then you will probably need to use a spare room in its entirety. If on the other hand you only want a few dwarf autoflowering plants for personal use then consider a closet grow. Most people opt for something inbetween. The height of the room needs to be a minimum of 4feet (1.20m) which restricts you to dwarf autoflowers under an LED grow light system; ideally you want it up to 7 feet (2.10m), especially if using heat producing HIDs. When deciding the size of your grow room, remember that you are also going to have to factor in space (either internally or externally) for fans, extractors and tubing, etc etc. 

Available location of grow room

Remember that external elements can effect your grow room’s environmentals. An attic grow may need heat added during winter but more heat extraction during summer. Think about where repair men etc may need access: you don’t want to have to choose between no hot water or dismantling your grow because the indoor grow room is in the same place as the boiler

Security & Secrecy

You don’t want to advertise your marijuana grow room. Smell is going to be a problem and even with a carbon filter on your extraction tubing, you don’t want it venting directly into a shared space. Sound is also an issue; the combined noise of ventilation equipment with the electrical hum can be a giveaway to those in the “know”. Consider carbon filters and exhaust silencers to cut down on noise and smell pollution. Insulating the room can also reduce noise. Be aware that some grow rooms have been discovered due to “suspicious activity”. Nosy neighbours may wonder why you keep popping into your suddenly noisy shed, so be aware of being watched as you go to and from tending your growing cannabis plants. You may need to consider the impact a grow room has on your children’s lives if they can no longer bring friends over because the room is too obvious a fact (although if this is the case, first you should question whether or not you should be growing at all) 

Availability of Services

This should go without saying, but you are going to need access to water (and a means of disposing of it) and electricity. Carrying buckets of water through the living room may not go down well with your other half[/toggle_content] [/toggle]   Once you have determined the size and location of your indoor grow room, you need to think how you are going to construct it. A small grow can be hidden within a large wardrobe or built in cupboard (as long as you remember to factor in air vents etc), or you can buy a  ready made “grow tent”. It is generally cheaper to make your own space to the size you need. Whatever you choose to build the grow room out of, you need to consider the following: 

  • Ventilation and air flow.

Your plants need good ventilation to breathe, so you have to consider how to make your extractor work most efficiently. Making the grow room as air tight as possible helps this. The airflow intake should be on a low level at one side, the air out take on the opposite side up high (because heat rises).  If you can avoid your air intake coming from outside as cold air will shock young plants.

  • Safety.

You’re going to be working with electricity and water, so make sure the two don’t mix!  Be organised: keep wires off the floor using neat cable tacks. Label the plugs. Use good quality timers with the correct ampage for the light system being used. No matter whether growing in soil or hydroponics, make sure any excess water drains safely. In fact if your indoor grow room is above ground floor its a good idea to “carpet” the entire area with builder’s plastic up to just above skirting board level in case you have leaks.

  • Creating the right environment.

Temperature needs to be controlled using either heating (possibly with the case of LEDs) or more likely heat extraction. Humidity should also be monitored – and a rH gauge is useful for this. During seedling stage humidity needs to be high (which is why many gardeners use a propagator) but even in vegetative growth, a relative humidity of 65 – 80% will increase the growth rate.

  • Organisation.

An organised room is also easier to keep clean, and a clean room is much less likely to fall foul of marijuana pests and diseases. If possible remove carpets as they keep dust and mites, and retain any spilt liquids. Just outside the room you need shelving and storage for nutrients, pH pens, calibrating fluid etc. Pen and paper is also handy for observational notes. If the grow area is more than 80cm wide you will probably need two access points to reach all the plants.


  1. The area needs to be light tight. This is important for two reasons.
  2. You don’t want light escaping from the room. For one thing this is a waste of light, but also it makes the indoor grow room visible (and thus vulnerable)
  3. You don’t want light entering the grow room. Cannabis plants are photoperiod and therefore will be effected by changes in the light cycle.

The inside area needs to reflect light. You’re paying for this light in size of light you buy and the electricity it uses so you need to maximise the light efficiency. Reflected light can increase the amount of light the plants receive by around a third. Artificial light will reduce with distance, so it is important to contain and direct the light within an appropriately sized area for the marijuana light.  

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