Stoney Tark edited on: March 16, 2023 8 minutes read

"Growing indoor Cannabis plants can be a straightforward process that requires a vegetative stage and flowering period. Understanding what happens when the plants are under 18 hours of light and the correct temperature and humidity guidelines can be advantageous as a beginner grower. In this article, we explain everything you need to know and some top tips to consider."

18/6 Explained

If you are new to growing indoor Cannabis plants and have heard the numbers 18/6 and 12/12, then this simply means the hours of light the plants receive. Cannabis plants are phototropic, meaning they respond to long and short darkness periods, so keeping them in a vegetative state is easily done.

By setting your timer to produce 6 hours of darkness, the Summer months are effectively mimicked indoors with the same daytime temperatures and humidity levels. On the basis that when growing indoor Cannabis plants you can keep the darkness period to a maximum of 6 hours, then you can control the final height and shape before flowering under 12/12.

- Cannabis plants will only focus on growing a strong root base and foliage.

- It is during this time the plants produce stems, leaves, and no flowers.

- Some growers use 24-hour lights on regime to keep plants in a vegetative state.

- Cannabis clones should be taken off plants under 18/6.

- Cannabis clones need to be left under-18 hours of lights and 6 dark.

- There should be absolutely no light breaks entering the grow room during darkness.I Only Want Big Yielding Cannabis Seeds.

For many experienced growers, getting big yields and a solid return on investment can be the main priority when growing Cannabis. Commercial-scale operations that are number-driven and dependent on profit margins and investors will demand high-yielding Cannabis seeds.

If your goal is to get as many grams of dried flower as possible, or you only plan to make hash or extracts with the crop, then we recommend Big Bud, Green Crack, Blue Dream, Original Glue. Chem Dog, Super Skunk, and Critical as these are all big procedures that are capable of harvesting 500-800g/m2.

The Correct Temperature

Use a digital hygrometer that comes with a sensor. Once you set this up inside your indoor grow room, it allows you to see both temperature and humidity recorded over a 24-hour interval.

If you cannot fall in the optimal temperature zone, then it is a good idea to use a heater inside the grow room, that can be put on over the light's off period. Monitor the temperature and humidity and find the perfect balance.

Relative Humidity Levels

Now that you have the timer set in place and understand the day and night temperature difference, the next thing is the humidity levels present. Growing indoor Cannabis during 18/6 requires high humidity levels close to the 70% mark. The most accurate way to do so is using a hygrometer to obtain a digital reading, and can see the highest and lowest parts of the day at the touch of a button.

This basically means the indoor environment should replicate the warm, wet, and sticky hot Spring to Summer months. By replicating the great outdoors inside, Cannabis plants can photosynthesize and grow new stems, leaf tissue and the root ball. The stomata that exist on the underside of the leaf prefer a warm and wet environment to be as efficient as possible, and to provide the plants with an exchange of carbon dioxide for oxygen and glucose.

- Humidity levels should remain consistent at 65-75% even during lights off.

- Hygrometers will produce a digital reading of both temperature and humidity.

- Seedlings and clones will struggle to grow under dry and harsh conditions.

- When supplementing CO2 indoors, humidity, and temperatures should be high.

- Using a humidifier can provide the perfect amount of moisture content in the room.

- Using a dehumidifier can eliminate excess levels of moisture in the air.

Fresh Air Is Essential

Providing a fresh stream of air blowing around the top and bottom parts of your Cannabis plants is key when growing Cannabis plants indoors. As fresh air from outside is pulled into the grow room, the stomata will uptake and convert the available carbon dioxide, so using oscillating fans is an excellent way to do this.

Using multiple fans turning at different speeds and heights from one another is the cheapest and most effective way to achieve the ideal setting, and will eliminate the risk of stagnant air and a powdery mildew infection.

3 Top Tips To Consider

Tip #1: Invest in a humidifier that can be placed inside the grow room or tent. Combined with the air currents produced by the fans, the temperature, and humidity will be perfect. Humidifiers can come in all sizes, so working with a small-sized one that fits inside a 1.2-meter tent, for example, is a good idea. Dehumidifiers also serve the same purpose in the event your outside air source is very wet.

Tip #2: If you notice that once your lights are turned off, the temperature spikes all the way below 15 degrees Celsius, then using a heater can help raise those nighttime readings. You can always invest in a temperature controller unit that will turn on the heater when the sensor detects that drop.

Tip #3: Set up your oscillating fans at different heights in the grow room, and make sure they are moving at different times from each other. The air currents created from this simple method will keep your plants cool, fresh, and thrive.

Nirvana Seeds’ Conclusion

Providing the best start for your Cannabis seeds and clones by making sure you follow these vegetative guidelines, will produce the best plants. We recommend investing in a good timer, hygrometer, humidifier, and ideally 2-3 oscillating fans, and being vigilant and staying on top of your room when growing Cannabis plants indoors!

Stoney Tark

Stoney Tark has been involved with cannabis for over 15 years. During this time, he has become head writer for the long-standing magazine; Soft Secrets, a position he has held for the last ten years, alongside writing for every other main publication.

Author of Stoney Tark’s Top Tips on Growing Cannabis, host of The Roll Models Podcast, breeder and sponsored by SANlight LED. Stoney is well versed in many systems and methods of growing, including, Organics, Hydroponics, Breeding, and Hash production. 

Well known in the public eye for his easy-to-understand and detailed breakdowns of all things related to cannabis. 

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