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Ideal marijuana lighting for your winter grow. Cabin with colorful sky.

Ideal Cannabis Lighting For Your Winter Grow

As fall comes to a close and winter sets in, cannabis growers have harvested their outdoor grows and reaped the fruits of their spring and summer toil. With flower from outdoor grows cured and continuing to fine cure in their mason jars, attention shifts to indoor or greenhouse grows since outdoor growing is no longer an option. Either a greenhouse with supplemental lighting or an indoor grow space will ensure continued cannabis production during the frigid winter months.

A grow room provides a warm, friendly environment for cannabis. With proper temperature, humidity and room to grow, cannabis will thrive and produce excellent quality that’s on a par with flower grown outdoors. Likewise, a greenhouse provides the protection the plants need during the winter and also allows the grower to harness the natural light needed for optimum growth—almost. Since the days grow shorter, supplemental lighting will trick plants into growing as they would during the long days of summer. Let’s examine the lighting needs for both of these options in more detail.

Winter Greenhouse Grows

To provide the optimum 18 hours of light that plants need during their vegetative phase of growth, good high-pressure sodium (HPS) lights will serve your needs nicely. The size of the greenhouse will determine the size of lights that are necessary, but most commercial grows will require 1,000-watt lights at the correct intensity to simulate the long days of summer. The natural daytime rays will become increasingly dimmer, so sufficient light at the correct angles, duration, and distance.

HPS lights are optimum for flowering and are the industry standard for growing premium cannabis. To accurately simulate summer lighting, you will need to increase the amount of artificial light each day, as the natural daylight outside continues to diminish. Winter daylight is slightly shorter each day, so a plan of action for increasing light duration and intensity will be necessary to simulate summer. The plants will continue growing as they would outdoors during growing season or indoors in a grow-room setting. With a schedule to increase lighting duration, you want to eventually reach a full 18 hours of light, a combination of natural light shining through the greenhouse glass and the light shining down on the pants from the HPS simulated sunlight. Once you reach the full 18 hours, the lighting duration will have to grow shorter to simulate the shortening days of late summer and fall and the onset of flowering. Since the sun sits lower in the sky during winter, you want to provide supplemental light at the overhead summer angle.

With a good, fully equipped greenhouse and some help from supplemental HPS lights, there’s no reason to halt production during the winter. Instead of packing it in, your late fall and winter grow can kick off as soon as your fall harvest is complete. Production will remain constant and you will enjoy a bountiful harvest all year long with the expected financial and personal rewards. In a greenhouse, you can control the light to make it any season you wish.

Winter Lighting for the Indoor Grow

Lighting for indoor grows can remain the same year-round, for obvious reasons. Other than adding supplemental heat, the plants remain unaware of changing seasons outside, so indoor growing practices remain the same regardless of the date on the calendar. When growing indoors, there are many lighting options with a variety of fixtures and hood style to maximize light intensity and manipulate direction.

Indoor commercial growers rely on clones for consistent, high-quality production. Clones will be several inches tall when placed into the growing environment, so HPS lighting is perfect right from the start. Light-emitting diode lamps LED lights are gaining rapid popularity in the cannabis industry and provide another option for indoor growers. While LED lights cost more than typical HPS lights initially, they consume less electricity, so the cost of operating them is lower. Eventually, anyone who invests in LED will recoup the extra money spent to purchase them. LED lights also runs cooler than HPS, so they won’t increase the temperature as much in the grow area, and they are safer overall.

Many growers who plan a winter grow indoors grow from seed. Growing with seed is quite different from growing with clones, so metal halide (MH) lighting is a great option for very young cannabis sprouts. Metal halide does a particularly good job of growing very young plants and helping them develop a root system. For initial fast growth, MH will provide a small advantage over HPS. The MH lights cause rapid growth initial development while HPS prove more effective in the later stages of plant growth. After the first two or three weeks, the cannabis plants will appreciate a lighting change. Switching from MH to HPS will boost plant branching and secondary root development. The use of HPS lighting is particularly beneficial during the flowering stage of plant growth, when plants really fill out and add a great deal of size with the development of fat, sticky buds.

Separate lighting fixtures, hoods, and ballasts exist for both MH and HPS lights. Because these types of lights cost quite a bit of money, investing in both of them might not be practical unless you have a good budget for your grow. Fortunately, there are ways around this to avoid spending too much, while still enjoying the benefits of using both MH and HPS.

Conversion bulbs are effective in changing lighting from MH to HPS. The size of the lights is identical, but the rays they emit are noticeably different. The MH light emits a very bright white light compared to the HPS conversion bulb, which has reddish-orange rays. The HPS conversion bulb effectively replicates the HPS rays of a true HPS bulb, while using a MH setup with MH ballast and hood.

Better yet, there are conversion ballasts that will change from MH to HPS with the flip of a switch. Although the conversion bulbs work quite well, the conversion ballast works even better and completely converts to using true HPS bulbs. When the time comes to switch from MH to HPS, merely flip the ballast switch from MH to HPS and change the light bulb from an HPS bulb to a true HPS bulb. The HPS light from this setup is true HPS instead of a close replication from a conversion bulb.

Both of these options allow growers to benefit from the different MH and HPS light rays and enjoy the best of both worlds. Whether using a conversion bulb or a conversion ballast, there is no need to overspend and buy completely different lighting systems specifically for both MH and HPS.

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Although some growers prefer to grow outdoors, there is no reason why they can’t continue to cultivate cannabis outside of the growing season. Whether utilizing partially artificial sunlight when growing in a greenhouse or completely artificial light when growing in an indoor grow room or building, the grow can go on. For some commercial operations, having the grow continue is essential to the business’s bottom line. Multiple harvests annually greatly increase yield and profit. So, flip the lights on next winter and enjoy a winter grow and harvest. There’s no reason to let factors like seasons and nature stop you!

Luis Cordova
Luis Cordova

Luis Cordova is a distinguished author, and renowned expert in cannabis cultivation, who possesses a Master's degree in Plant Biotechnology and Pharmaceutical Science. As a valued contributor to highly esteemed publications such as Cannabis Training University and Maximum Yield Magazine, Luis has emerged as a trusted source of guidance and knowledge in the cannabis industry. Having written thousands of informative articles, Luis is widely recognized for his comprehensive expertise on cultivating cannabis, both indoors and outdoors.

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