Growing cannabis is, without a doubt, a warm-weather activity. Even indoor gardens can be negatively affected by the elements. But that doesn’t mean you have to shut down your grow when the temperature drops. With the right knowledge, planning, and determination, you can cultivate top-shelf marijuana year-round. In this comprehensive article, we’ll go over our top tips on how to grow cannabis in winter.
Best Cannabis Strains for Cold Climates
One of the most limiting factors when it comes to cannabis cultivation is genetics. No matter how dialed-in your grow may be, the genetics of the plant will determine its yield, potency, and overall quality. Therefore, choosing a strain that can perform well in cold climates is a must.
Regarding photoperiod cultivars, Indicas are your best bet for cold climates. Landrace Indica varieties from Asia and the Hindu Kush mountains have adapted to much chillier temperatures than tropical Sativas have. Strains such as Bubba Kush and Indiana Bubblegum can thrive in cool, dry environments without sacrificing yield or quality.
Autoflowering strains also are an excellent choice for winter grows. These cultivars descend from the Ruderalis subspecies—a variety of cannabis that has adapted to the cold climates of Central and Eastern Europe. As a result, autoflowering plants are particularly hardy and able to withstand suboptimal conditions. Moreover, these plants typically reach maturity in just 8 to 12 weeks, allowing you to squeeze in an extra harvest outdoors in early spring or late fall.
Cannabis and Temperature
Temperature is, of course, the most immediate concern when growing cannabis in winter. Cold weather can stunt or kill the plants even when cultivating an Indica or autoflowering strain. So, if you want to learn how to grow cannabis in winter, you’ll need to learn how to control the temperature in the grow room.
How Temperature Affects Cannabis
Cold weather can wreak havoc on a cannabis plant, creating a host of problems for growers. At the root zone, temperatures below 54 degrees Fahrenheit will slow the plant’s metabolism. This will impede its ability to uptake oxygen, water, and nutrients through the root system. It will also slow the enzymatic processes that promote plant growth. Consequently, growth will slow or stop entirely, and the plant may eventually die unless moved to a warmer area.
In addition to slowed growth, cold temperatures can create the perfect environment for mold growth when paired with moisture. If rain, snow, or frost stays on the plants for extended periods, botrytis and other fungal infections can take hold in the garden.
What Is the Best Temperature for Cannabis?
To prevent stunting or killing your plants, you’ll need to know the optimal temperature range for healthy plant development; however, the right amount of warmth depends on what stage of growth the plants are in.
During the vegetative growth period, cannabis plants perform best in warm weather, between 70 and 80 degrees Fahrenheit. This is because, when grown outdoors, the plants are typically vegging during the peak summer months.
The flowering period usually occurs during autumn, when the temperature starts to drop. Therefore, flowering cannabis plants thrive when exposed to slightly cooler temperatures, between 68 and 75 degrees Fahrenheit.
Considering nighttime temperatures for indoor and outdoor gardens is also vital. The general rule of thumb is to keep nighttime temperatures no more than 10 to 15 degrees cooler than daytime temperatures.
How To Control the Temperature in the Grow Room
As we’ve established, the ideal temperature range for cannabis is quite narrow, and falling below it can have deleterious effects on your plants. Therefore, it’s essential to learn how to manage the amount of warmth in the grow room. Fortunately, there are several tools and techniques to do so.
If you can’t afford to heat the entire building, consider investing in an electric space heater. These units come in various sizes and can heat a grow room or tent without breaking the bank. Look for a space heater with a built-in thermostat that will automatically regulate the temperature. Just keep in mind that the heated air will be dry, so avoid letting the space heater blow directly onto the plants.
Heat mats are another valuable tool for winter grows. Although they are typically used for seed germination, heat mats also are effective at keeping the root zone at the ideal temperature. Just make sure to invest in a safe, well-built one that isn’t prone to catching fire.
One easy way to increase the temperature in the grow room is to adjust your lighting schedule. HID lights produce a significant amount of heat; even LEDs can warm up a small tent by a few degrees. So, consider keeping the lights on during the night and turning them off when the temperature rises during the day. You could also switch from 18 to 24 hours of light during the vegetative growth period to generate more heat.
If heaters, heat mats, and grow lights aren’t cutting it, you may need to insulate your grow room or tent. Fortunately, there are many affordable options for insulative fabrics. You could even drape some blankets over the outside of the tent to trap the heat from the lights. Just don’t create a fire hazard!
Humidity and Cannabis
The grow room’s humidity is another less obvious variable that can be challenging to control during the winter. As stated before, rain, snow, and frost can create a breeding ground for mold. But even indoor gardens can have issues with humidity during the cold season.
You may have noticed you’re more likely to suffer from chapped lips and dry skin during the snowy season. This is because cold air can’t hold as much moisture as warm air. Therefore, the humidity levels will typically drop substantially during the winter—even indoors. So, if you want to grow cannabis in winter, you’ll need to understand how to regulate the humidity in the grow room.
How Humidity Affects Cannabis
The amount of moisture in the air plays a significant role in how cannabis plants uptake water and nutrients. If the relative humidity (RH) level is too high, the plants won’t be able to evaporate water from the leaves. When this happens, growth slows or stops, and the plants can no longer uptake nutrients and water from the soil.
On the other hand, low RH levels also can negatively impact plant growth. If the humidity level is too low, the plants will evaporate too much water from the leaves, causing the roots to uptake more water and nutrients. This increased absorption of nutrients can lead to overfertilization, which may stunt growth. If left unchecked, overfertilization can lead to wilting, burnt leaves and flowers, and, eventually, death.
What Is the Best Humidity Level for Cannabis?
As with temperature, the ideal humidity level for cannabis depends on the growth stage the plants are in and the type of strain you are growing. Generally, the early stages of plant growth will require higher RH levels than the later periods, and Indicas will require slightly less humidity and Sativas.
During the seedling stage, cannabis plants need high RH levels, usually between 65 and 70 percent. As the plants progress to the vegetative period, you can lower the humidity to between 40 and 70 percent. Once flowers begin forming, the humidity should be reduced to between 40 and 50 percent. Finally, RH levels should be at their lowest during the late flowering period, between 30 and 40 percent.
How to Increase the Humidity Level in the Grow Room
During the winter, it’s not uncommon for RH levels to drop as low as 20 percent indoors. Therefore, it’s vital to understand how to increase the moisture in the air, especially during the early stages of plant growth.
One way to increase humidity is to lower the power of your exhaust fans. This will help to keep warm, moist air inside the grow room. If you are using a tent, you could also zip up the tent to trap moisture. Just make sure you are giving the plants enough ventilation to prevent mold growth.
Another strategy is to spray water or a foliar feed on the leaves and soil. Just make sure not to spray anything on the plants during flowering, as it can contaminate the flowers or cause bud rot. An alternative solution would be to surround the plants with open containers of water. As the water evaporates, it will raise the RH level in the room.
The most effective way of raising the humidity is to use a humidifier. As with space heaters, there is a variety of humidifiers on the market that vary in price and capacity. Choose the right size humidifier for your room, and you’ll be able to control the RH level quickly and easily.
Can You Grow Cannabis Outdoors in Winter?
In short, no. You can’t grow marijuana outdoors in winter unless you live in a region with very temperate winters and low rainfall. Most areas either become too cold or too rainy to grow cannabis successfully.
If you are gutsy enough to try growing outdoors in winter, you’ll need to keep the plants’ roots warm with heat mats, protect them from rain and snow, and be ready to move them indoors if the temperature drops too low.
Final Thoughts on How To Grow Cannabis in Winter
Growing ganja doesn’t have to be a three-season activity. With the right tools and know-how, you can cultivate killer cannabis any time of year. By following the advice in this article, you’ll be able to select the right strain, control the temperature and humidity in the grow room, and keep your plants healthy and happy no matter the weather outside.