Marijuana is a hardy plant, but it isn’t invincible. Those interested in growing marijuana need to consider their location and how it may affect your plant’s growth -- for example, if you are somewhere further from the equator, you will need to decide which kind of strain to buy to fare well with shorter summers.
Winter growing is an entirely different ball game. When growing outside, it simply isn’t possible. Even if the temperature were right, the light certainly wouldn't be. Remember, marijuana plants need more than 12 hours of light per day during their vegetative stage, and winters simply won’t provide that. Some locations in the south manage to get two harvests per year, but that is the only case where winter growing may possibly work.
That being said, growing marijuana indoors is entirely different. In fact, many growers prefer to grow their crops during the winter, as that is the time when heat issues are no longer a problem. HPS lights can actually be more efficient because they emit heat and allow the temperature to remain between 70 and 80 degrees consistently.
When people grow indoors in the winter, it’s important to remember to use HPS lights rather than LED lights or CFL lights, which don’t emit heat like HPS lights do. The temperature must always stay above 60 degrees Fahrenheit, or else they will not have a good harvest -- and perhaps won’t even survive. Their growth will slow down significantly, and the plants may never recover fully. This is especially the case if they are exposed to cold repeatedly or for extended periods of time, or if the temperature is frigid.
Heating and humidity during the winter
Some growers, especially those who live in locations with particularly cold winters, often elect to use other forms of heating to keep their marijuana plants warm. These can be heating pads, fan heaters, or just simple insulation. Raising the plants so they aren’t on the ground can also make a difference. Generally speaking, heating a room is cheaper than cooling it, so even with these extra expenses, it should cost less than if you were growing in the hot summer months.
You will also need to think about the humidity. Humidity generally drops inside during the winter months, and marijuana plants require 40% or higher of relative humidity. Unfortunately, it is not uncommon for the indoor humidity to be below that benchmark.
The reason for this drop in humidity inside of buildings is due to the heating system being used. A heating system generally pulls in cold air from outside and warms it, but it does not add any moisture to this air before pumping it into the room. The cold air outside doesn’t hold as much humidity as warm air would, so the air is already dry, even once it warms up.
One way to combat this is by buying a humidifier for your grow room. If you don’t, your plants are going to need a lot more frequent feedings of water (because they will be transpiring more frequently and in higher amounts), and it could affect the nutrients and how they are being absorbed by your plants. Humidity is vital, as nutrient burn or toxicity is common in plants that are growing in an environment with low relative humidity. Luckily, a lower relative humidity is not too difficult to combat, and it will not affect your plants as strongly as if they were trying to grow in winter temperatures.
The sunlight is weaker in the winter months, meaning greenhouses won’t be as productive as in the summer months. If you provide artificial light during the daytime hours and then cover your greenhouse with Mylar during the nighttime hours (which keeps excess light out while maintaining proper heat), you can have a very successful winter greenhouse harvest.
Outdoor winter growing
Even if you live in a southern climate that makes it possible to grow marijuana outdoors, it will be an unpleasant experience. Even when the temperatures are high enough, certain areas of the world with warm winter temperatures are likely to have major storms and other intense weather occurrences that could have a negative impact on your crop. That being said, marijuana plants that are located in a sheltered area might be just fine.
No matter what, a winter yield will almost always be lower and more disappointing than a summer yield. Areas such as India, Thailand, and Hawaii might be okay when they are growing a sativa plant, which is meant for more tropical climates than some other strains.
Plants grown in California can be harvested as late as mid-December, so a very late harvest is possible (rather than planting and growing your plants throughout the middle of winter). Still, the harvest is not going to be as strong as if you grew primarily during the spring and summer months.
Written by Robert Bergman, founder of ilovegrowingmarijuana.com. Robert has been passionately exploring and experimenting with cannabis seeds for over 20 years and shares these insights to educate growers avoid mistakes and to fully capitalize on a bud's potential and get the most out of a marijuana plant.