Well, it’s that time of year again. Unless you’re in the deep south, there aren't many places left in the US that can provide a suitable grow environment for an outdoor marijuana garden. By now, all of California’s outdoor crops have been harvested and the same goes for Colorado, Washington and the rest. Every growers’ attention has turned to their secret indoor “Christmas crops” and stash grows: those special boutique gardens that mix the scent of great ganja with that of pine trees, nutmeg and mistletoe.

So with that in mind, we here in the HIGH TIMES cultivation department thought we would remind growers of some important factors that can make all the difference in the holiday harvest. And since we are moving indoors, what better topic to discuss than light.


As dedicated horticulturalists, we need to understand that there are more advantages of sunlight (over artificial lighting) than simply the sheer strength of the sun. And to understand these advantages, we need to know about spectrum and the role it plays in photosynthesis.

Photosynthesis is the process whereby our plants use light to create sugars to use for energy and in cannabis plants, THC production. To serve this process, growers need to supply their plants with a powerful light source that can provide a proper spectrum: this will ensure maximum sugar production during photosynthesis.

When light hits the leaves of a plant, each leaf uses various pigments (most notably chlorophyll a, chlorophyll b and carotenoids) to trap light energy and extract photons, which are vital in converting the light energy into chemical energy. These photons combine with water to provide the plant with the needed chemical energy to fix carbon dioxide (CO2) molecules into sugars, carbohydrates and other organic compounds the plant will use as food.

So, what does spectrum and light color have to do with photosynthesis? Spectrums are actually differently sized wavelengths that give the appearance of color to the human eye. These wavelengths are important because plants absorb different colors of light in varying amounts for photosynthetic processes. Supplying your plants with the colors they can absorb most readily and in high quantities assures better photosynthesis and more food, resulting in bigger yields and more resin production for super-potent pot.

Unfortunately for the indoor grower there is much debate over which frequencies of light are best for plants. Scientists know a plant’s absorption rates during photosynthesis, and these absorption rates are shown in the plotted curve graph (Photosynthesis Action Spectrum) below. The graph depicts the sun’s natural light spectrum overlaid for comparison to where the sun’s light is most efficient in photosynthesis. You’ll notice that where the sun’s spectrum is lacking -- on the sides in the red and blue light -- are also the same areas where plants are most efficient at processing light.

Some people argue that plants are simply more efficient at using red and blue light because they have evolved to become more efficient at these wavelengths. Less-experienced horticulturalists may believe that supplying their plants with only red and blue spectrums of light is best for photosynthesis since the plant is most efficient at absorbing these wavelengths. However, depriving your plants of the full range of light spectrum would be very much like depriving a growing human of their full range of vitamins. Every color of light, just like every mineral in a vitamin, plays a vital role in a plant’s development.

However, there is something a bit more tangible for plants when it comes to the red wavelengths of light spectrum. Starting at around the 600 nanometers (nm) mark, the red frequency of light carries the highest concentration of light energy -- measured in photons -- over any other color frequency. These photons are what the plant and leaf pigments harvest from light and use at a catalyst for photosynthesis. The more energy a plant can harvest from light, the more food (sugars) it can produce, thereby increasing both yield and potency. So while just red light alone will stretch and retard your plant’s internal processes, additional influxes or supplementations of red (and blue) light can boost your plant’s development and make for a healthier harvest.

Like anything else, the best solution is balance. To that end, many cannabis cultivators will use both HPS and MH lamps simultaneously to provide as much spectrum coverage as possible. Some growers will complement their HID lamps with additional supplemental grow lights such as compact fluorescents (CFLs) or LED-based lamps, which provide the reds and blues. These growers usually achieve excellent results with very healthy crops.

Here’s to your secret little baby in the back bedroom or under the stairs. May your harvest be heavy and your head be high.