What Cannabis Needs to Grow

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In addition to light being the catalyst for carbohydrate production in plants, light or more specifically the length of time light is absent, otherwise know as a plant's dark period, determines when a plant begins to flower or bud, which ultimately initiates reproduction. This is what is known as a plant's photoperiod.

A plant's photoperiod is the response in the plant to the changing lengths of day and night. The cannabis plant's initiation of flowering is the process most frequently associated with changing the plant's light cycle from 18-24 hours oflight per day to 12 hours oflight per day in a 24-hour period.

Like most living things, a plant needs water, air, light, food, and warmth. These are the essential elements required to grow almost any type of plant, not just marijuana. Take anyone of these away and your plants won't grow very well. Let's take a look at each of these factors so you can start to understand what you'll have to provide for your plants when growing indoors.


About 80% of a living plant's weight is water. Besides being used as a transportation-medium, the majority of the water absorbed by the roots will be used to keep a plant cool. This works the same as with human beings; by evaporating water, heat is dissipated, which results in a cooler body. The rest of the water is used in the plant's photosynthesis process. Photosynthesis is a complicated process where the plant builds carbohydrates from water, nutrients, CO2, and light-energy. These carbohydrates are later combined with other chemical compounds absorbed from air and soil and transformed into new plant growth.


It seems that everybody understands the importance of light and water in the process of photosynthesis. But another factor, carbon dioxide (C02), is always underestimated.

The CO2 formula tells us that carbon dioxide is a molecule made of one carbon and two oxygen atoms. The carbon atom is of importance here because oxygen is just waste, at least to the plants. There is only one carbon atom in each molecule of CO2 and there is only about 0.3% CO2 in normal air, which isn't much. Because of this, it is important that marijuana plants have a constant supply of fresh air.


Light energy is used to form carbohydrates like sugar, starch and cellulose that are used by the plant to build and repair plant tissue. Of course this can only take place if there is a source of light available. The light we see from the sun is a mix of all colors. Plants use mainly blue and red light, depending on which growth phase they are in.

Since you plan to grow indoors, where the sun refuses to shine, you have to use another light source. One problem with using artificial lights is that normal bulbs don't give enough light for a plant to thrive and they emit light in the wrong colors. The only types oflight bulbs able to provide enough light for plants to grow properly and in the right color spectrum are Metal Halide (MH) bulbs for vegetative growth and High-Pressure Sodium (HPS) bulbs for flowering. These bulbs are used in High Intensity Discharge (HID) lighting systems, which are capable of giving plants the powerful illumination they require.

For the vegetative (growing) phase of a plant's life cycle you need more of the cool, blue light that MH bulbs provide. If you are just growing seedlings, you could also use fluorescent lighting, but that's an entirely different discussion. Marijuana that is in the flowering (budding) phase needs more of the orange-red light provided by HPS bulbs.


Okay, we have light, water, and air, now it's time to eat. When humans eat, our meal is digested in our stomach, another weird chemical process involving things you may not want to know about. Our cells can't do anything with, let's say, a piece of banana, so it's ripped apart into smaller elements which our bodies' cells can use for growth and other processes. Among other things, acid is used to split complex molecules into easier-to-handle smaller molecules and elements.

A similar "elemental breakdown" applies to marijuana plants as well. Plants can't nourish on the complex molecules found in the medium at which

they root, be it soil or any artificial medium. Plants are not equipped with a stomach, so they are in a bit of a disadvantage. Plants have to pre-digest their food, so to speak, by using CO2 and light energy. Through photosynthesis, they are able to break down their nutrients into elements that they can use to grow, repair, and eventually flowering and produce seeds.


And finally, since eating and growing means work and all work costs energy, this is where warmth becomes important. If a certain temperature is not reached, growth will happen at a slower rate or if it's really cold, there will be no growth at all. Maintaining a certain range in temperate is especially true for roots, which should be kept about ten degrees cooler than the air around your plants.