How to Build a Weed Grow Room [6 Easy Steps]

1)  Light Proofing

To begin with, we must ensure that the environment is completely isolated from natural light. For optimal flowering, the cannabis plant needs 12 hours of darkness and 12 hours of light, without interruption, because this could not only cause a decrease in yields, but also and above all the total destruction of the crop. This is why you should monitor the space reserved for the crop to make sure that light does not pass inside. If not, get a dark tape to seal holes and cracks. A growing area that is not isolated from light can easily ruin the harvest, as plants get confused. One of the most predictable effects is the birth of male flowers on female plants due to stress. It takes very little time for a few male flowers to fertilize all female plants, resulting in buds filled with seeds.

A good grower always controls his plants, so that all male flowers are immediately removed. It takes a few weeks for the male flower to spread active pollen. It is also quite common for plants to have difficulty entering flowering when rays of light manage to pass through the grow-room, resulting in a very small harvest. Above all, make sure that any appliances in the growing room are actually intended to stay in that room, as the lights that remain on emit a lot of light and can disturb the plants’ night sleep. Isolate all lamps and lights from the light with adhesive tape.

2) Airtight

Once our plants are well into bloom and produce wonderful buds, their smell also begins to develop. Plants start to diffuse a scented but also a strong smell, so it is important that the space reserved for cultivation is designed in such a way that it is completely airtight.

The area reserved for cultivation must have as few cracks or holes as possible, through which the smell of ganja could pass, even better if it does not have any. When the plants start smelling, you will visit them so often that you will get used to them without any problem and you may convince yourself that your plants are almost odourless, while your neighbours or co-tenants will suffer because of the strong smell they produce.

Another important factor is the safety benefits of a hermetically sealed space, as it allows the internal climate to be controlled. It is very important to create a favourable climate if you want to get the best out of your plants. So, when preparing the room, check that odour outlets and drafts are not possible. A third important aspect is the impossibility for all undesirable parasites to enter the cultivation area. A good culture space is a kind of isolation cell where nothing comes in or out without your permission.

3) Climate

Once all the above-mentioned aspects have been respected, we have achieved the final objective of developing the space reserved for culture, creating an ideal climate where plants can grow to become true giants, growing and blossoming at an incredible speed. The climate must be constant and uniform throughout the room: it is therefore necessary to use one (or more) fans to ensure good air circulation. This will make the plants thicker and strengthen their feet and yield more than plants that have grown without a fan. If you have a good budget, it is worth investing in a thermostat, hygrometer or thermo-hygrometer.

You can connect the thermostat to the extractor ventilation helix so that you can set the desired maximum ambient temperature, say 28 degrees. If the temperature exceeds this threshold, the extractor is activated to reduce it to 28 degrees. The hygrometer can also be connected to the extractor to guarantee a constant percentage of humidity. If the environment becomes too humid, the air is sucked out until it reaches the right level of humidity. With a dimmer, you can adjust the operating speed of the ventilation propeller, so that it can be rotated constantly at low speed to always bring clean air into the room.

4) Air Moisture

To adjust the atmospheric humidity, you will need to use an ambient humidifier. These devices are not very expensive and represent a useful investment. They are often sold with a built-in hygrometer: all you have to do is set the necessary humidity and the humidifier will take care of it.

The effect is miraculous, especially during the growth phase. The plant can grow twice as fast in a humid environment, reducing the required growth time. There is a big difference between heating a large culture room and a small room. In confined spaces, it is easy to increase the humidity in the first few weeks, but try to do so in a large room. In reality, it’s just as simple, but you need to have many expensive appliances and if you’re just starting out, it’s better to stick to a limited budget for your room layout.

At this stage, you can spend a reasonable amount of money to properly isolate the cultural environment: everyone’s. In addition, we will have to make sure that on the other side of the room, at the bottom, there are holes to let the air in. These favour the renewal of the air, which is rich in carbon dioxide (CO2). On the other side of the room, on the ceiling, we will place an extraction pump that is used to suck up and expel the hot air. The hot air rises: this is why the pump must be placed at the highest point. By equipping the pump with a carbon filter, we can simultaneously eliminate any strong odours. A carbon filter and a vacuum pump go hand in hand and are absolutely essential when setting up a garden like ours. One filter will suffice for about five harvests, or one year.

The pump must have a capacity adapted to the dimensions of the space reserved for cultivation: it is therefore necessary first to calculate the volume of the room in question. Let’s go back to the school for a moment: we multiply the length by the width by the height of the room and we get its volume. Always choose a pump with a capacity slightly higher than the actual volume of the part. During the hot summer months, this will be very useful to maintain an acceptable temperature.

So opt for a higher capacity: for example, for a 500 m3 space, we could choose a suitable fan for a room of 750 to 1000 m3.

The big advantage is that during the coldest winter months, we can run it slowly, without consuming too much energy, and during the hot summer months, we can remove the butterfly valve and quietly keep the temperature below 30 degrees Celsius. A large fan running at medium speed is much quieter than a small fan running at full power.

In addition, if you want to expand the culture room in the future, you would not need to buy another fan. It is impossible to buy a fan that is too large: in the worst case, it will be too small. And it doesn’t make sense to run a fan at full power when you could renew the fresh air in the room in the same way by running it at an intermediate speed. By making air inlet holes at the back of the room and exhaust on the top, we create an air flow that will carry clean and enriched air from the bottom to the top of the room by blowing on the plants.

This is excellent for plants, as it allows them to get the most out of the fresh air before its CO2 content is exhausted, sucked in and expelled. To keep parasites away, we use nylon tights or special tights, placed on the air intake holes so that nothing can fly or get inside and to avoid a future infestation. Of course, it should not be forgotten that light should not enter the room through the holes. PVC L-pipes work well to get air in without allowing light to enter.

There are a thousand ways to ensure an adequate supply of air in the room; they are all correct, but there are two basic rules to follow: bring in air preferably from below and prevent light from entering the room. If it is not possible to make a hole for the pump, the best solution is to buy an economical door and drill a hole for air extraction: a method very often used by professional farmers.

5) Square Meter

Enough talking! The real work awaits us: to physically build the room reserved for culture. Few things are enough: one square meter (everyone has one somewhere, in the attic, in the cellar or in a spare room). You need a wood stapler, a saw, a white or black plastic sheet, a drill, screws, scissors, a few pieces of wood… and a square meter.

We are about to build an internal screen for the culture room. Suppose you use only one square metre of a large room: it is appropriate to isolate this cultural space from the rest of the room, which you can use for something else. If you don’t, the whole room will smell when the plants start to flower. The big advantage of building a screen is that the light from your lamp will be used to the maximum. Light is directly proportional to weight, i.e. the amount of light a plant receives largely determines its final yield. By building a screen around the square meter and then covering it with white plastic sheeting that reflects the light, it is retained on the plants and within the space reserved for cultivation. Otherwise, the light would spread throughout the room and you would lose a large part of it.

Make sure that the side walls around the plants are white and reflect light well – this is the most economical and simple way to increase yield. Mylar is currently the best product on the market to reflect light on plants. It is a little more expensive than a black-white plastic tarp, but it reflects about 99% of the light emitted by the lamp, reflecting it back to the plants. Mylar must be suspended so that it remains as tight as possible to be able to function perfectly. When designing the growing area, it is important to ensure that the walls reflect light, regardless of whether they are white walls or plastic sheeting.

To build a screen, it takes half an hour of work, if you have the necessary equipment at hand. Cut eight pieces of wood about 1.20 m long and six about 1.70 m long (because this is the ceiling height of my cellar). The ideal length should be slightly less than the height of the room where the crop space is located.

If the piece is 2 meters high, it will be necessary to cut 8 pieces of about 1.97 m. In other words, a few centimetres should be subtracted from the actual height of the room. The first step is quite simple: we make a wooden frame by fixing two 1.2 m wide pieces to two 1.70 m high pieces (in my case). With an electric drill, it’s very fast: we press a piece on the two parts to be fixed together, we drill a hole and we screw them in order to fix them. When our wooden frame is securely attached, we can place the black-white plastic sheet on top, positioning it so that it is tight. To do this, simply attach the tarpaulin with the stapler. The excess tarpaulin can be cut off after it has been fixed. We thus obtain our first reflective screen, to which we must attach another screen, by proceeding in the same way as with the two previous ones, simply by using a piece less than the 1.70 m wooden props. We use the 1.70 m axis on the screen we have just built and we attach two 1.20 m and one 1.70 m pieces to it.

Put the tarpaulin down and staple it several times, cutting off the excess. We now have two screens attached to each other. In this way, we avoid making two separate and distinct screens. Let’s do the same thing on the other side: another screen attached to the existing forestay of the first screen. We now have three reflective screens firmly attached to each other. This structure must now be installed on the chosen square meter to create your growing space. As mentioned earlier, the screens are slightly larger than the space reserved for cultivation, as sufficient space must be left to install the fan and similar devices. Finally, let’s build another independent screen using two 1.20 m long pieces of wood and two 1.70 m long axes. The individual screen, which is not attached to the others, is the entry door to your culture area.

We install it against the open side of the box of the three reflective walls and our growing area is completely closed. All you have to do now is move the screen holder to control and take care of your plants. The light from the lamp will now remain inside the grow-room and you will then notice the difference when you harvest. The smell of the plants stays inside and can be easily expelled using an extractor equipped with a filter, so that the rest of the room can be used for something else. Of course, the most creative growers can transform their grow-room into a real jewel for themselves.

6) Collection Rack

A space reserved for cultivation must be able to be kept clean easily: that’s why I decided to build a kind of “harvesting bin” inside which to place the plant vases. We therefore build a frame-shaped structure 1.10 m wide, the length you want and 15 cm high.

The bin is covered with the same white and black reflective tarpaulin (making sure it has no holes, not now or ever). A bin of this type makes it much easier to clean and keep clean and diseases will have a much harder time settling in. All waste, such as soil, dead leaves and fallen water, ends up directly in this bin. Once the harvest is done, it is very easy and quick to clean the bin for the next harvest. If you don’t use a harvest bin, as many farmers do, the space you use for cultivation will quickly become a dirty room from floor to ceiling.

In addition, a harvest bin like this is very useful if you need to rinse the crop. “Rinse” means to remove excess nutrients or fertilizers from the substrate (in this case, from the plant silt). If the plants receive too much pure water, the nutrient residues are washed, as well as any salts accumulated due to excessive fertilization (the salts are contained in the fertilizer). Some growers simply decide to rinse every two weeks to keep the substrate as healthy as possible. If you have a collection bin, you can rinse the plants without any problem and without dirtying your growing room. Another advantage is that when you grow in the ground, you can let the whole tank fill with water and nutrients and the plants absorb what they need themselves.

The effect is the same as for a vase plant placed on a tray. In fact, you made a huge tray. The advantage is that it becomes very difficult to give too much fertilizer to the plants, since it is they who will decide how much they have to absorb. If you have to be away for 3 or 4 days, you can simply leave the harvest bin full and the plants will have enough water and nutrients every day. The tank is therefore also used as an automatic irrigation system. You can then switch to a hydroponic system at low and high tide. So, in short: the aim is to create a space reserved for culture, impermeable to light and airtight, where on one side of the room the fresh air, rich in CO2, enters from below, flows upwards and exits on the other side. A sufficiently large extraction pump ensures that the air is changed and the fans circulate the fresh air that enters with the air heated by the lamps, so that there is the same temperature throughout the grow-room.

Simply add reflective walls to maximize the effect of light and a collection tray to keep everything in order. That’s all you need. The space reserved for cultivation is now ready to accommodate plants!

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