Growing Medical Marijuana Indoors

For indoor gardening, you must supply the plant with everything that nature provides outdoors. That includes a planting medium with space large enough for the roots, light, air circulation, satisfactory temperature, and, of course, water and nutrients. Unless your indoor garden space is incredibly bright and receives direct light throughout most of the day, the plants will have ot be energized using electric lights.



Cannabis grow lights

Some gardeners prefer to use fluorescent or compact fluorescent lights, but most gardeners gravitate toward 400-, 600-, or 1000-watt high pressure sodium lamps that can be found on the internet and at indorr garden shops. With the unit, you’ll find special ballasts along with a reflector.

Plants use light to combine the elements in water and carbon dioxide to produce sugar and release oxygen. Sugar is the primary building block for tissue growth—including bud growth—and is used to power metabolism or the essential life process. The more light energy the plant receives and can use, the faster and more dynamic the growth will be. In the same space, a garden grown under a 400-watt lamp will only produce 40% of the bud that a loop-watt lamp would. Gardens generally yield about 3/8 to 1 gram per watt of lighting. A gardener using a 400-watt lamp will usually harvest between 6 and 14 ounces every two to four months. Under a loop-watt lamp, the harvest can increase between 13 ounces and a full 2.25 pounds.

Depending on the variety, plants require between 45 and 60 watts input per square foot of canopy. A 400-watt light illuminates between 6 and 10 square feet while a 1000-watt lamp illuminates between 16 and 20 square feet. Indices and indict hybrids needs less light to thrive than sativas and sativa hybrids.


Temperature in cannabis grow room

In order to maintain adequate temperatures in the growing space, the heat produced by the lamps needs to be eliminated. The two best ways of achieving that goal are an air-cooled reflector or a water-cooled reflector. These units will enclose the lamp in a cooling system that is not a part of the grow space. The air or water is odorless and can be used for heat in another space.

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Temperatures can also rise as a result of the absorption of light, much of which is converted to heat. The humidity will also build up causing the plants to practically mine the CO2 from the air. Without CO2, the plants cannot produce the vital tissue-building sugars, and growth will stop until the CO2 is replenished. Because of all of this, the growing space must be ventilated with fresh air.

Of course, simple ventilation can be achieved by opening a curtain or door, but some gardeners prefer complex methods like using flexible tubing and an inline fan. Occasionally the ventilation line is controlled by a thermostat or humidistat, but some growers like to keep the ventilation going whenever the lights are on.

Planting medium

Cannabis planting medium hydroponic

Indoor gardeners can choose between growing in planting containers with planting mix and using hydroponics. Hydroponic systems use a non-nutritive rooting medium that provides nutrients by adding fertilizer to the water. Using hydroponics effectively requires more skill and accuracy because there are no natural buffers in the medium. It will not be covered in this section, but there are plenty of books on this subject.

Growing indoors

Growing cannabis indoors

Whether you’re starting with sexed seedlings or clones, the plants should be grown in containers tilled with a high-quality enriched indoor planting max. For the sake of convenience, three-gallon containers aren’t that heavy and they also give the roots enough room to grow.

Clip the top bit of growth off of the center stem when you transplant the young plants. Keep the lights on between 18 and 24 hours per day. Longer light periods correlate to accelerated rate of growth to flowering size.

After about three weeks, the plants should be between 1 and 1.5 feet (30 to 45 cm) tall and ready to flower. At this point, you should change the light cycle to 12 hours of darkness and 12 hours of light. Use an automatic timer so that the light goes on and off at the same time each day without running the risk of human error. It’s important to avoid interrupting the dark period, even briefly, with light. Green light is the only safe light to use while in the dark garden. Also at this time, you should change the fertilizer to a special flowering formula. In 7 to 10 weeks, depending on the particular variety, the top buds will be ripe. Buds hidden underneath the top canopy should be left on the plant as they will ripen in around 7 to 10 days.

Thanks for reading and good luck growing your own medical marijuana. Please leave comments or questions below and don’t forget to download my free grow bible.


Robert Bergman

Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations. His passion for growing lead him to develop his own Gold Leaf strain. Now, Robert is dedicated to sharing his knowledge with the world.... [Read full bio]


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    4 comments on “Growing Medical Marijuana Indoors”

    1. I really appreciate all the information about growing that you have made available. Now just waiting on the grow bible. But yes I think you might have a new disciple.

    2. I love the grow guide, my problem and question is yield how do I get the most yield out of my plants I had a harvest recently after everything It had about 7 grams not good. I also ordered seeds from a different place and both orders were taken and destroyed by customs please help