Growers Network Staff

January 20, 2019 4 min read
January 20, 2019
4 min read

How to Grow Cannabis 242 – Annuals and Lighting

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Today on How-to-Grow Cannabis, Growers Network explains why different lights or lighting setups are better during certain stages of the cannabis life cycle.


In our last How-to-Grow Cannabis article, we explained how plants use visible wavelengths of light for photosynthesis, and briefly touched upon how different colors are ideal for different stages of cannabis’ life cycle. Specifically, cannabis plants in propagation or vegetative state prefer bluish-white light, and cannabis plants in flowering state prefer warmer, orange and yellow light.

To accommodate for this change in preference during the plants’ life cycle, many growers will change the color settings of their LED light, or swap out their HID bulbs for a different type.

But why do we do this? Why do cannabis plants prefer different color temperatures?


Annuals


Anybody who pays attention to gardening has heard about annuals. Annuals are plants whose natural life cycle lasts about a year. They grow from a seed, mature, reproduce, and die within a year. Annual plants are differentiated from biennial plants (lives 2 years) and perennial plants (lives longer than 2 years).

Cannabis is considered an annual plant because it will follow the annual cycle under normal conditions. And like many annual plants, cannabis will switch between different stages of its life cycle depending on the lighting conditions.
In the wild, cannabis will grow from seed in late winter/early spring, enter vegetative state in late spring, maintain vegetative state through summer, and enter flowering state in fall before dying in late fall/early winter.

  • Spring light is generally bluish-white.
  • Summer light is generally white.
  • Fall light is generally red/yellow.

Cannabis has evolved to respond to these color temperatures most, which explains why these lighting conditions are ideal. Some growers I have spoken to also inject extra blue and UV light during the final stages of flowering for a last push before the plant expires.

With all that said, many growers still choose to stick to a single lighting regimen for their plants. Since photoperiod and scotoperiod determine the transition points for cannabis, growers will often elect to buy the bulbs that exhibit the highest PPFD numbers and simply change lighting schedules. Large scale grows will often choose this method for practical reasons. This method works, but is less efficient than a gradual transition in color temperature.


Picking Lights Appropriate For Your Needs


In our How-to-Grow Cannabis 112 article, we briefly explained different lights and their utility. Today, we’re going to go further into depth and help you decide what lights might best suit your needs.

Lighting Type Pros Cons Price Range
Fluorescent Bulbs Energy Efficient
Easily Replaced, Generally Cheap
Heat production low
Great for small plants
Low PPFD output (this can be good for seedlings/cuttings, not so good for veg or flower)
Low light penetration
Must be suspended close to plant
$35-$250 per fixture
Induction Lamp Long Life (approx 2 years)
Energy Efficient
Heat production low
Heavy
Take up large amounts of space
PPFD output diminishes over time
$100-$250 per fixture
Metal Halide (MH) Lifespan of about a year to a year and a half
White spectrum
Fixtures take up minimal space
Higher Heat Output
Older HID lighting technology
Less electrically efficient
Contains mercury
RF Interference from Ballast
$60-$120 per bulb
$100-$250 per ballast
$30-$250 per reflector
Ceramic Metal Halide (CMH) / Light Emitting Ceramic (LEC) Moderate heat production
Newer HID lighting technology
Blue-White spectrum
Fixtures take up minimal space
Contains mercury
RF Interference from Ballast
$50-$110 per bulb
$100-$250 per ballast
$30-$250 per reflector
$200-$500 for a complete fixture
High Pressure Sodium (HPS) High PPFD output
Orange spectrum
Fixtures take up minimal space
High Heat Production
High electrical demand
Contains mercury
RF Interference from Ballast
$30-$100 per bulb
$100-$250 per ballast
$30-$250 per reflector
$200-$500 for a complete fixture
LEDs Energy Efficient
Heat Production Low
Long Life (approx 2-5 years)
Can produce output in UV spectrum
Most models allow variable spectrums
PPFD output diminishes over time
Tend to be expensive
$350-$2000 per fixture
Plasma Lights / Light Emitting Plasma (LEP) Spectrum very similar to sun
High PPFD output
Energy Efficient
High heat production
Tend to be expensive
$400-$1000 per fixture

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About the Author

Hunter Wilson is a community builder with Growers Network. He graduated from the University of Arizona in 2011 with a Masters in Teaching and in 2007 with a Bachelors in Biology.