One of the most beautiful, yet challenging, elements of indoor cultivation is the environmental control and manipulation of one’s growroom. While it’s evident that outdoor gardeners enjoy the pleasantries of working under blue skies, enveloped in fresh air, there’s no denying their crops are still at the mercy of Mother Nature.

Environmental constraints such as rain and humidity often affect the quality of one’s harvest, especially compared to that of indoor gardens. Truly passionate indoor horticulturalists take a great amount of pride in their growrooms and the fine balance it takes to create an artificial environment in which plants thrive.

For these indoor enthusiasts, cleanliness, sophisticated equipment, air flow, humidity levels, temperature balance, and proper CO2 levels can bring as much satisfaction as a good-looking crop.

Along this line, there is perhaps no more explicit example of a perfectly balanced synthetic cultivation environment than that of a sealed growroom.

Sealed growrooms are those that have no exchanges between the interior and exterior of the cultivation space. Ideally, they are sealed tight from any air or light leaks.

By creating such an independent ambient atmosphere, indoor growers have control over temperature, humidity, and CO2 without having to consider (in much detail) outdoor environmental constraints.

With these things considered, here are a few tips for those interested in building a sealed growroom.

Air Conditioners and Grow Rooms

As sealed growrooms don’t feature the traditional air exchange elements of intake and outtake fans, they require air conditioners to create an ideal environment for indoor plant growth. For most cultivators, the use of a mini-split AC system makes the most sense for sealed rooms.

Traditional home AC systems and window units are much more difficult to work with in terms of light and air leaks as they generally require large holes to be put in growroom walls.

Conversely, a mini-split AC system features thin copper tubing running from a compressor that operates outside to a head unit in the room that expels cool air. This copper tubing is less than an inch thick and is easily run into a room and sealed off with some caulk.

CO2 Systems and Grow Rooms

Another consequence of sealed rooms not having air-exchange is that CO2 injection systems must be implemented to supplement for the loss of fresh, CO2-rich air. Not that this is bad; CO2 enrichment is the primary motivation for cultivating in a sealed environment as CO2 levels can be precisely controlled and monitored in these environs.

While average, ambient CO2 levels in growrooms range anywhere between 300-500 ppm, indoor cultivators can reach stable CO2 levels around 1500 ppm. However, it is much more difficult to maintain an ideal CO2 equilibrium without a properly sealed growroom (not to mention gardeners will waste far more CO2).

Read more about CO2 supplementation for indoor grow rooms.

Growing Plants in Bedrooms and Basements

For a growroom to function properly with its delicate balance of air conditioning and CO2 injection, it must be sealed properly. Thankfully, eliminating light and air leaks is a relatively simple task for indoor growers cultivating in bedrooms and basements.

Windows are large obstacles to overcome when sealing a basement or bedroom growroom. Many cultivators like to start by covering an entire window up with a piece of soundboard or plywood. This will help lessen exterior noises and will add an extra layer of insulation from outdoor environmental elements.

After this initial layer of protection is placed over the window, its best to cover the entire wall (including the covered window) with a layer of photo reflective panda film to further insulate the room from light and air leaks.

Doors pose an even more serious impediment when trying to completely seal a grow space. Since cultivators generally need these doors to access their gardens, they cannot simply cover them up with soundboard and panda film. Hence why many growers turn to zipper doors. Zipper doors keep an airproof and lightproof plastic layer over a doorway while still allowing access to the indoor garden space.

Read More: The Basics of Light Deprivation Cultivation

Growing Plants in Rooms Inside of Rooms

Many indoor cultivators opt to build a free-standing growroom within a room. There are several motivations for this, most of which involve lessening the impact of an indoor grow on a home and creating a more efficient growing environment out of the original room (namely, garages).

Of course, there are challenges. As fabricated growrooms generally don’t feature drywall, insulation, and professionally mounted doors, they lack many of the light and air control features present in a bedroom or basement constructed by a professional builder. Therefore, there are a couple of routes to take in sealing these fabricated growrooms.

First, one can build out the entire frame and ceiling of the growroom, as if building a home. Once built, the entire thing can be wrapped in six-millimeter-thick black plastic, which should be carefully stapled to the frame. This thick plastic will ensure that there are no light or air leaks.

Secondly, one can cover the growroom walls with plywood, as would be seen in traditional home building scenarios. While drywalling isn’t necessary, caulking up all the cracks between the plywood boards and the floor and walls will remove all elements of light and air leaks.

No matter where you plan to build your indoor growroom, take the time to make sure it is properly sealed. That way you can completely control your plants’ environment and work towards truly maximized yields.

Finally, don't forget about grow room ventilation strategies.