by Nebula Haze
Temperatures are dropping in many parts of the world and unfortunately, cannabis plants don’t like the cold. In fact, most cannabis strains grow significantly slower once the temperature gets under 60°F (15°C), and freezing temperatures can cause major injury or even plant death.
This cannabis plant is happy to be inside out of the cold weather
Cannabis plants thrive in the winter as long as you protect them from the cold
Keep roots warm and up off the cold floor
A plant growing outdoors is often more resistant to cold than indoor plants. Part of that resistance comes from the fact that their roots don’t experience big temperature fluctuations. Cannabis plants don’t like “cold feet”.
But you can capture that power indoors, too. If you’re growing in a basement or garage, it’s common for the floor to be cold. When that’s the case, put your plants on a tray or some other barrier to prevent roots from sitting directly on the chilly floor.
Plants are droopy and sad when their roots get chilly. Keep the plant container off the ground when growing in a cellar or other space that has a cold floor.
Be prepared for a power outage
One challenge for growers in wintry climates is the impending chance of their electricity going out during the winter months. Indoor growers rely on electricity to keep plants alive, especially in the winter, so it’s a good idea to prepare ahead of time.
Learn how to prepare cannabis plants for a power outage
Avoid LED Grow Lights (Use CMH, LEC, or HPS if Possible)
LED grow lights are amazing for their ability to produce a lot of light without much heat and as a bonus make plants more heat-resistant. A perfect combo for growers who are struggling with a hot grow room.
However, if you deal with cold temperatures, LEDs are a poor choice. Not only do they produce little heat, but they also make plants less resistant to cold in general. On the flip side, HID grow lights like CMH/LECs and HPS produce a lot of heat to help keep plants warm. HPS in particular also produces a lot of infrared light, which helps raise the internal temperature of leaves to help keep plants warm from the inside out.
I live in California but it gets cold in the winter and our home doesn’t have any built-in heating. At night the temperature can drop to 40°F (4°C) or occasionally even lower. We keep warm with space heaters in the living areas, but I prefer not to run a heater just for the grow room. That’s why in the winter I often grow with my HPS grow light. As a bonus, you get insane yields and potency from an HPS grow light in a cool grow area. HPS is a superior light when the temperature stays consistently under 75°F (24°C). I set the “night period” to be during the day and have the lights turn on at night when it gets cold so plants stay warm and happy.
I bring out my HPS grow light when the temperature drops. It puts off a lot of heat to keep plants warm. On top of that, the high levels of infrared light make plants more resistant to cold.
Switch timer’s on/off cycle so grow light is running at night
Let me elaborate a little more on changing the light schedule. It’s common to grow in a garage or attic that is an okay temperature during the day but too cold at night when the grow lights go off. In this case, change your plant’s light schedule so the grow lights turn on at night (during the coldest hours) to help equalize day and night temperature.
Hot grow lights help keep plants warm. If it’s getting cold at night, change your timer so grow lights turn on in the evening during the coldest hours.
However, in order to get most cannabis plants to start flowering (making buds), you need to give them at least 12 hours of complete darkness every day, which means grow lights need to be off for 12 hours/day. For some growers in a wintry climate, a 12-hour dark period (even during the day) will send the temperature plummeting too low.
But did you know there’s a type of cannabis that will make buds even if you leave your grow lights on for 24 hours a day?
Auto-flowering strains let you keep your grow lights on for 24 hours/day, which helps keep plants warm in cool grow areas
“Auto-flowering” strains automatically start making buds when they’re about a month old and are typically ready to harvest at 2-3 months from germination, regardless of the light schedule. This means you can leave your grow lights on 24 hours a day, which can help plants stay warm.
On top of that, auto-flowering strains often tend to be a little less sensitive to cold since their ancestor, the ruderalis hemp plant, originated in the Siberian tundra. Although most auto-flowering strains today are heavily hybridized, some strains have kept their ability to handle the cold.
The ruderalis hemp plant (the ancestor of all auto-flowering strains) evolved in the freezing environment of northern Siberia
Modern autoflowering plants are ruderalis hybrids that have been bred for yields, bud quality, and potency, yet some strains still carry resistance to cold
Strain Makes a Difference
As I mentioned, some cannabis strains can handle the cold much better than other strains. If possible, it helps to pick a cold-resistant strain if you know that your grow area may experience chilly temperatures on a regular basis. Learn where you can get seeds.
Recommended cold-resistant photoperiod strains
- Frisian Dew
- Hindu Kush
- Matanuska Tundra
- Midnight Mass
- Orange Candy (aka Naranchup)
Recommended auto-flowering strains for the cold
One advantage of cold temperatures is it tends to bring out colors like purple and pink
Jump to…
12 Cool Growing Tools You May Not Know About
10 Odd Realities (With Pictures) About Growing Cannabis Plants
Teach me the basics of growing weed
