How can I protect my Indoor marijuana plants from the cold?

Indoor Growing in Cold Climates
Growing cannabis indoors seems like the logical plan if you live in an area with colder climates. Battling with the elements - below freezing temperatures, frost, torrential downpours and violent winds - become a minimal concern. But there can be some disadvantages to taking your growing operation indoors.

You may have space limitations. If you're not fortunate enough to have a basement or empty storage room, you'll need to put some serious thought into what space can be used most efficiently. The good news is that it is possible to generate decent yields even if you have to grow weed in a small space.

Consider the number of exterior walls when deciding which room to convert to a grow space. It's important to pay attention to how cold the room gets at night when the temperature can dramatically drop. If your area tends to have significant drops, extra insulation may be required.

That's another factor to include in your cost analysis. An indoor operation will require additional supplies and equipment which means additional expense for the start-up process.

Sometimes it's better to have a few limitations and be able to control your growing environment, than to experience a total crop loss due to some unpredictable weather.
Choose the right strain

Look for strains labelled with a Cool/Cold designation. These are specifically bred for outdoor growing. They are capable of flowering even in northern latitudes.

Choose Indica strains over Sativa strains. Sativas are normally bred with tropical genetics and require warmer climates. Strains bred with genes from Afghanistan, the Netherlands, Canada, and the Himalayas do well in cold-temperate climates.

Breeders have created a multitude of autoflowering seeds that do well in northern climates. They are popular for growing operations with outdoor facilities because their maturation is not inhibited by the length of day.

Our catalogue of Amsterdam-bred seeds lists some of the most weather-resistant, enduring seeds available. Holland's Hope, Afghan, Early Bud, New Purple Power, and Swiss Miss have the potential to grow just about anywhere.
Choose the right grow light

Old school HID systems emit a great deal of heat, as well as light. Keeping cannabis plants in vegetative growth with an MH bulb under an 18+ hour light cycle is actually easier in cold weather and a simple method to preserve mother plants and/or cuttings during the winter months.

Flowering with HPS grow light and vegging with MH bulbs usually requires serious air cooling. The old school grower can turn cold weather to his/her advantage and save some cash on the air conditioning bill at the same time. Some even add extra lights to boost yields when the weather gets cooler.

LED lighting systems are rapidly overtaking HID bulbs as the cultivation lamps of choice for Millennial weed growers, but the technology is still to be perfected. LED lights run cooler, because they emit almost 75% of their energy as light. This is fantastic most of the time and usually makes for easy environmental control in the grow tent.

However, LEDs can run too cold during the winter months. The simple solution is to turn up the heat. Unfortunately, this might negate the electric bill savings made by running the low wattage drawing LEDs.

High RH may also be an issue with LED systems in cold weather, a dehumidifier may also need to be added to the grow show and definitely during the bloom phase.

CFLs are more or less redundant during prolonged periods of cold weather, even the highest wattage bulbs available, with 300W, cannot generate sufficient heat to curb a frosty winter.

Bud rot is a real threat for growers cropping in cold weather with next generation lighting like LEDs and CFLs. Hydroponics and LED grow lights can be a recipe for disaster in cold weather, as both root rot and bud mold can be real threats if feed water is below room temp and RH exceeds 60% during flowering.

Maintaining environmental control year round is the only long-term solution; keep an eye on those thermometers and make adjustments when necessary. It's a whole lot easier to heat a grow room in winter, than it is to cool a sweltering HID grow show in high summer.

Old school HID growers may be able to avoid turning on the heating during the dark cycle if they run their lights during the cold winter nights. Daytime temperatures are usually a little higher, so it might be possible.

LED aficionados face the prospect of running the heating virtually nonstop. Perhaps a combo of HID and LED is the smartest compromise in freezing conditions for the modern indoor cannabis grower.

We almost forgot to mention cropping cannabis in cold weather has the huge advantage of increasing the chances of certain strains displaying beautiful lilac and deep purple shades every weed grower covets most.
Humidity must be managed

Temperature and humidity are important factors to control for any pot grower, but cold-climate growers need to pay even more attention.

As a rule, warm air holds more water which means higher humidity. Cold air is often referred to as "dry" because it does not hold as much water. Cold air is usually low in humidity.

The relative humidity (RH) for maintaining the best growing environment varies based on the stage of the plant. For young plants, during the vegetative stage, the recommendation is to keep humidity levels between 40-60%.

If you have trouble maintaining the right humidity during your cold weather growing, here are a few simple tricks to raise the level:
Use a spray bottle to manually add water to the air
Moisten soil surfaces, but avoid over-wetting
Drape dampened cloths or towels around the grow space
A large capacity humidifier might be worth the investment

It's important to note that plants are more vulnerable to a variety of molds in colder temperatures. If the environment is too damp, mold grows rapidly, destroying entire crops.