best climate to grow marijuana

Hot Tips For Growing Weed In Cold Weather

Cannabis is a plant that loves being warm, sure, but that doesn’t mean you can’t grow it in other climates. With a bit of preparation, enough knowledge, and just a pinch of technical ability, you might just be able to grow healthy cannabis plants even in cold conditions.

We all know that cannabis grows best in areas with warm summers and plenty of sunshine. But, being such a versatile and hardy crop, you might be wondering whether it’s possible to grow cannabis in cold weather. Thankfully it is, but there are some key tips and tricks you’ll need to keep in mind.

In this article, we’ll walk you through everything you need to know about growing cannabis during those chilly winter months.


Getting It Right From The Start – Picking The Perfect Genetics

Every cannabis grow is dictated by genetics. In turn, if you’re planning a winter or cold weather grow, your best bet at achieving a respectable harvest is investing in the right genetics from the start.

Ideally, you’ll want to look for strains with genetics linked to cooler areas of the globe. Indica-dominant strains and landrace varieties from mountainous areas of Asia, for example, tend to be much better suited to cooler temperatures than sativas.

Autoflowering strains are another great option for growers living or growing in cold regions. Cannabis Ruderalis, the variety of cannabis bred with indicas and sativas that gives descendants their autoflowering properties, is native to Central/Eastern Europe and Russia, and is renowned for being especially hardy. Plus, the fact that autos can go from seed to bud in as little as 8 weeks makes them optimal for sneaking in an extra early Spring or late Autumn harvest.

How Cold Weather Affects Cannabis Plants

There are 2 main concerns when it comes to growing cannabis in cold weather or winter. The first is shock to the plant’s root systems.

Healthy roots are the heart and soul of a healthy cannabis plant, and cold weather can directly impact the health of a plant’s roots.

Once soil temperatures drop below 12°C, a cannabis plant’s metabolism starts to slow down considerably. As it does, the plant will struggle to take up water, nutrients, and oxygen from its soil, and many of the enzymatic processes needed to fuel its growth will come to a standstill. Over time, the plant will likely suffer from stunted growth or may even start to wilt.

In some strains, cold weather may also trigger hermaphroditism, meaning that the plant grows both pollen sacs and buds, leading to self-pollination and dramatically decreased yields in turn.

Mold is the second major concern when growing cannabis in cold weather, especially if there’s moisture in the air.

Moisture from rainfall, snow, or frosts can build up and become trapped on a plant’s leaves or flowers, triggering mold issues that can be extremely hard to get rid of. That, in turn, can cause the flowers of your plants to rot well before they’re ready for harvest.

How Cold Can Cannabis Get?

This leads to another question: How cold can cannabis plants get before problems arise? Well, to answer that question, we first have to consider the perfect temperature for cannabis plants.

For the most part, they’re happiest at temperatures between 20-25°C, depending on which stage of their life cycle they are in. Vegetating plants, for example, like it warmer, as they’re usually in that stage during the peak summer months. In that same way, flowering plants tend to like slightly cooler temperatures, as they’re usually in this stage around the beginning of autumn. Meanwhile, the ideal soil temperature for healthy, stable root growth is between 15-20°C.

Straying a little outside of these ideal temperatures, though, won’t kill your plants. After all, cannabis growing in the wild isn’t always exposed to that ideal range. However, if you’re growing indoors and have the opportunity to meticulously control every aspect of your grow, staying within these temperatures will ensure your plants grow at their best.

Getting That Extra Late (Or Early)-Season Crop

One of the reasons you might be considering growing weed during the coldest months of the year is to get in an extra harvest, either before or after the growing season. If that’s the case, we recommend planting autos and germinating them either late in the fall or, preferably, later in the summer.

Depending on the flowering time of the particular strain you’re growing, your plants could be harvest-ready either by mid-winter (if you germinated your seeds in fall) or mid-fall (if you germinated in summer).

Note that this technique only works in regions with a mild winter or a warm spring. Don’t try this technique if you’re living in an area with harsh, cold winters and unstable spring temperatures. In these areas, you’ll need to build a greenhouse to protect your plants from the elements.

What Effect Do Cold Temperatures Have On Flowering Cannabis Plants?

Many indoor growers opt to bring down the temperatures in their grow room during the bloom phase. This helps mimic the natural temperature drop plants would be exposed to when growing outdoors, and can also help promote bud development as the plant prepares for winter and focuses on reproducing. Many growers also find that gradually dropping the temperatures in their grow room can help encourage their plants to produce buds with purple hues.

Can You Grow Cannabis Outdoors In Winter?

No. Unless you live in an area with very mild winters and low rainfall, we don’t recommend growing cannabis outdoors during winter, as you’ll usually end up with sickly plants and/or poor harvests.

If you do try your hand at keeping a bunch of outdoor plants during winter, make sure to follow these tips to keep them healthy and get the best possible results:

  • Keep your plants’ roots warm. Using heat mats to keep your soil temperatures above 12°C can help minimize the stress to your plant’s root zone and promote healthy vegetative growth and flowering.
  • Protect your plants from rain or snow. Remember, any humidity trapped on your plant’s leaves or buds can cause serious mold issues.
  • Know your dates. If you have your plants growing outside at all, remember to bring your plants indoors before the temperatures outdoors get too cold.

Avoid Light Stress Or Revegetating (When Moving Your Plants Indoors)

If you need to bring your cannabis plants indoors to shelter them from the harsh winter, make sure you do so carefully. Pay close attention to the daytime hours and temperatures, and do your best to match those conditions indoors.

If your plants have started to flower, you’ll need to be even more careful. If you give them more light indoors than they’ve been getting outside, they may revert back into their vegetative cycle. This process is known as revegetation, and causes extreme stress for the plant.

Force Flowering Outdoors

If you can’t move your plants indoors in time to save them from the winter, plan ahead and consider force-flowering your plants outdoors. The easiest way to do this is to cover the plants with a light-proof structure or fabric (like a tarp) during their new “nighttime” hours. This will give them the impression that the seasons are starting to change, and they’ll jump into the flowering phase accordingly.

Move Plants To A Greenhouse

Greenhouses essentially give you the freedom to grow weed all year round, given you have adequate control over the lighting, temperature, and humidity inside your greenhouse. If you’re considering using a greenhouse to grow your own weed, here are a few things to consider:

  • The initial cost of building and setting up a greenhouse can quickly add up and usually top the costs of setting up an indoor grow room/tent.
  • Greenhouses allow you to harness the power of the sun all year round (given your region gets plenty of sunlight).
  • Growing in a greenhouse helps keep your plants away from prying eyes.

Why The Old School Indoor Grower Welcomes Cold Weather

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 lighting 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.

Why The Next-generation Grower Needs To Turn Up The Heat In Winter

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 LEDs 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.

Wondering how you'll be able to brave a winter cannabis grow? Click here to learn all there is to know about growing weed in cold weather.

How to Make the Best Growing Environment

What makes the perfect cannabis growing environment? What does it take to get the healthiest growth and best yields from your indoor cannabis plants?

Consider a grow tent if you want a pre-made perfect growing environment for your marijuana plants!

5 Factors to Creating a Perfect Growing Environment
(from most important to least important)

  1. Light – Bright but not too bright
  2. Temperature – Comfortable for you, comfortable for your plants
  3. Air Circulation – Fresh air plus a gentle breeze
  4. Reflection – Cover your walls with a reflective material
  5. Humidity – Controlling humidity helps plants grow faster and can increase resin production

You need a great environment to produce the best harvest. A poor growing environment lowers both yields and bud quality!

Benefits of a great grow environment

  • Plants grow faster
  • Harvest bigger yields
  • Healthier, greener, and overall hardier plants
  • Higher bud quality (better bud density, shape, and trichome production)
  • Stronger bud smell and potency (THC and smells can get “burned off” if it’s too hot)
  • Plants are more resistant to common problems like over/underwatering, hermies, heat stress, light stress, bugs, mildew and but rot

Keep plants comfortable and they will reward you!

1.) Light

When growing cannabis, you want to give light that is bright but not too bright. The amount of light you provide is one of the major factors that will determine your yields, and with smaller grow lights your yields will be limited no matter what you do.

Light also changes how your plant grows. For example, the color spectrum of light can cause your plants to grow tall and lanky or more bushy and squat. Some grow lights like LED grow lights take advantage of a custom color spectrum to help your plants grow as optimally as possible.

The amount of light you give your cannabis is the main factor that determines your yields

However, it’s also possible to give your cannabis plants too much light, especially with big grow lights, so it’s important to keep grow lights the right distance away.

2.) Temperature

The long and the short of it is: If it’s comfortable for you, it’s probably comfortable for your plants.

Cannabis plants like temperatures in the 65-85°F (19-30°C) range and can start to run into problems when the plants are experiencing temperatures outside that range.

Optimal Temps for Growing Cannabis

3.) Air Circulation & Exhaust

Making sure your plants always have a gentle breeze and plenty of fresh air helps them grow faster. Good air circulation also helps prevent problems with white powdery mildew, bud rot, and common cannabis pests like fungus gnats or spider mites.

Basically, you want a gentle breeze moving over, through, and under your plants if possible. If all the leaves are being gently rustled, it’s perfect. You don’t want to point a fan directly at your plants because that can cause wind burn, but you also don’t want any leaves sitting in stagnant or hot air. A small oscillating fan or two in the grow space can work wonders.

In addition to making sure there’s air moving around in the grow space, it’s also important to vent out heat from your grow lights, especially if it’s getting too hot for your plants during lights-on. While many growers know they’ll need ventilation with powerful HPS lights, it’s important to note that ventilation can be just as crucial for LEDs, LECs and even fluorescent lights like CFLs or T5s if the total wattage gets high enough. For each light type, the higher the wattage, the more heat produced. If you notice the temperature is climbing above 85°F (30°C) on a regular basis, you should consider venting heat out of the grow area to keep the temperature under control. However, if the overall temperature of the entire grow room is too high, you may need to take more drastic actions such as getting an AC. Fans can move air around, but can’t lower the total amount of heat in a room.

4.) Reflection

You will get the most from your indoor grow lights by reflecting light at your plants. Instead of letting the walls of the grow space absorb extra light from your grow light, you can use a reflective material to bounce it back towards your plants. This allows you to squeeze more yields out of the same grow light without having to change anything else about your environment.

Flat white latex paint is a surprisingly cheap and easy wall material that has 85-95% light reflectivity. Yes, it’s true, simply painting your walls can actually increase your yields! There are also many other materials with great reflectivity, and some of the professional options work even better than paint.

5.) Humidity

Unless it’s very high or low, humidity usually won’t cause any major problems with your cannabis grow. However, there are a few tricks with humidity to get faster growth and more resin production on your buds.

Note: The optimal seedling humidity is closer to vegetative plants than clones. Try to avoid letting the humidity get over 60% for seedlings or it can slow their growth.

Perfecting Your Growing Environment

It’s important to realize that there is no one “perfect” growing environment. Just like people, each plant is a little bit different and may respond better to some environments than others. For example, some plants can better handle the heat or cold, and some plants aren’t as picky about good air circulation. But by taking care of the 5 factors of a great cannabis growing environment, you will ensure that your plant will be comfortable no matter what the strain!

And of course, if you run into any problems, diagnose your sick cannabis plant right away!

Learn which 5 factors are essential to creating the perfect cannabis growing environment! Getting this right will help your plants grow faster and yield more!