Growing Cannabis Indoors

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Growing Cannabis Indoors2017-11-29T11:25:33+00:00
cannabis gardening indoors

An indoor growing set-up can produce impressive yields and healing medicine.

Cannabis is a pretty hardy breed. In the correct conditions, most varieties require a minimal amount of fine-tuning and attention once they have been planted.  In non-Mediterranean or tropical climates, however, outdoor growing of cannabis can be difficult simply due to a lack of sufficient sunlight.

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How Do I Set Up A Grow Room?

Growing cannabis indoors in a specialized grow room (or even just a grow closet) gives the gardener the ability to control every aspect of their gardening environment. The planting of cannabis indoors also prevents theft, maintains privacy, and avoids most damaging pests.  Since medical marijuana users generally require only a small harvest, growing a couple of plants in the home is often a viable option.

Important Factors in Indoor Growing

Lighting Your Grow Room

To grow cannabis indoors, light – or more specifically, the balance of darkness and light – is the most important resource.  Very bright lamps are the best choice, though in sunny climates a combination of artificial and sunlight may suffice.

growing weed indoors good lights

Choose strong lighting such as HPS or LED bulbs to imitate sunlight.

High Pressure Sodium (HPS) bulbs are the most popular choice for growing indoors, though metal halide and even LED can work as well.  A minimum of 250 watts is required, though upwards of 400 watts is ideal.  The more intense the light source, the bigger, denser, and more numerous the buds.

In some cases, the amount of artificial light used when growing indoors can be reduced by using natural light during the brightest part of the day.  This means the grow room must be blacked out for the period of darkness, however.  Even the tiniest amount of light during this period can confuse plants grown indoors, and throw off their growing schedule, resulting in fewer or lower-quality buds.  Unsolicited light can even result in seeded (hermaphroditic) flowers, which are unusable.

What about distance from the plants?

Ideal lighting when growing indoors is adjustable.  As the cannabis increases in height, the lights must be moved away from the top of the plants; close enough to provide light but not so close as to cause overheating.  A hanging light can be placed on a chain, or a floor light can have an moveable arm to facilitate this adjustment.

Some lights have a built-in, air-cooled system.  They are generally enclosed in a glass case, with a fan pushing the heat through tubes and out of the grow room.  While this set-up allows the cannabis to grow quite close to the lamp without burning, it is not a requirement and without it, bulbs should be kept about two feet from the tops of the plants.

The grow room should be between 75 and 85 degrees Farenheit throughout the growing period, and cooler by a few degrees for the first few days (some possibly the periods of darkness). 

Maintaining the right temperature is important because:

  • If the space is too warm, the marjiuana plants will wilt;
  • If the space is too cool, plant growth may be slowed or stop completely as the cells become more and more sluggish.

growing marijuana indoors best lighting

Indoor Cannabis Growing Practicalities

Though many people who grow cannabis indoors use the hydroponic method, which does away with soil entirely, we will consider a soil-planted method.  The article How To Grow Cannabis with Hydroponics has more information on this modern (and widely embraced) alternative method.

What Kind of Pots Should I Use for my Pot?

Pots designed to allow the root system to breathe are the best choice for growing cannabis indoors.  Though the top of a plant breathes CO2, the roots breathe oxygen, so oxygen must reach them.  Drainage holes and a pan for water runoff are also essential, so your roots don’t drown or rot.  Stagnant water attracts mold and bugs, and should be removed manually or through a drainage system.

The Best Soil for Growing Cannabis

indoor growing marijuana in soil

Use organic soil and make sure your plants’ roots can breathe!

Organic potting soil with a partial base of peat or coco is a good choice when growing cannabis indoors.  Peat makes the soil porous enough for the root system to breathe. 

If the soil has additional nutrients mixed in – such as kelp or manure – the plants may not need further nutrients until they have begun to flower.  If there are no additives in the soil, a high-quality plant food works as well. By growing indoors, the gardener is able to better control what the plant absorbs (though soil may contain unknowns, as well).

Planting Your Germinated Cannabis Seeds

The cannabis seeds are placed about one cm apart, with more soil pressed gently on top (see Following Germination – you don’t want to press the soil too hard, or the little sprout won’t be able to push through).  During this initial period, the temperature in the grow room should be between 68 and 75 degrees Fahrenheit. The tiny seedings should break through the top of the soil within two to four days, but give them about a week before you start to worry, and definitely don’t dig for them!

Watering Your New Marijuana Plants

As the cannabis begins to grow, take care not to over-water – knowing the original weight of the potted plant can help determine when the soil is nearly dry.  Too much water can slow growth, and result in a lower yield once the cannabis flowers. Growing indoors gives gardeners the ability to control moisture levels just like other environmental conditions.

marijuana plants seedlings water

Cannabis Plant Growth Indoors

Watch your canna-babies grow!

In nature, cannabis, a flowering plant, grows in summer and bears its fruit – the buds – once daylight hours have begun to shorten.  This is why many strain descriptions mention October as the optimal time to harvest (in the natural environment).

When growing indoors, the actual season is not important, but the cannabis must be made to believe the seasons are changing.   A cannabis plant will flower when it begins receiving equal quantities of light and dark – in other words, 12 hours of each.  This allows the gardener to control when their plants begin to develop buds; they may choose to start flowering when the plants are quite small (about 2 weeks after planting), or wait until the plants have grown taller (as long as 3 months).

Whichever your preference, a vegetative stage of some length should always precede the flowering stage for best results, as this ensures your plants develop the strength and structure to hold a good yield of medicinal flowers.

How Long Is the Vegetative Stage?

growing marijuana indoors vegetative period

Let your plants build structure in the vegetative stage for at least a few weeks.

Exposing a cannabis plant grown indoors to bright light (artificial or sun) for 18 to 24 hours a day can keep it in a vegetative state.  Ideally, this period of growth without flowering should last four to six weeks.

Even if natural light is used to partially grow the cannabis indoors, during the vegetative state a lamp will be needed to supplement the sun.  The strength of the light is vital to proper growth for plants kept indoors.  Too weak and the plant may “stretch” – grow taller, but not bushy and leafy as it should.

In the vegetative state, the roots, branches, and leaves of the plant should grow, but the flowers, or buds, should not.  In general, the longer the cannabis is allowed to remain in the vegetation period, the more buds it will be capable of sustaining once the flowering period has begun.  This is another benefit of growing indoors.

Read More: Get all the details on the Vegetative Stage

How Do I Start the Flowering Stage?

cannabis flowering stage indoor growing

This stage will begin when the light changes to 12 hours of “day” and 12 hours of “night”.

Once the vegetative state is complete, a change in the amount of daily light will signal to cannabis grown indoors that the “season” has changed and flowering should begin.  The amount of light is lowered to twelve hours on, twelve hours off.  Now, the light must be as bright as possible.  Likewise, the darkness must be absolute to avoid confusing the plant.

During the first week or so of the flowering period, cannabis grown indoors will continue to grow – even doubling or tripling in height.  The buds will develop on and around the cola (stem) and among the leaves.  Many strains of cannabis, grown indoors or out, produce a great number of large buds, packed very densely together.

Though the flowering time should be determined by the readiness of the buds (the amount of amber resin, for instance), approximate times (for growing both indoors and out) are included in our descriptions of every strain.  Cannabis flowering times can be anywhere from 40 to 90 days, depending on the variety.  Once the buds are completely developed, they can be harvested and dried for medicinal or recreational use.

Read More: Learn about the cannabis Flowering Stage

This is a lot of information, but it’s all important to understand before you dive into germinating your cannabis seeds and planting them indoors! If you found this article helpful, help us by sharing it on Twitter! (We appreciate it!)

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