growing cannabis in greenhouse during winter

How to Grow Cannabis in Winter

If you think that growing cannabis in a European winter is impossible, then you’ve been misinformed. With the right conditions in an indoor growing operation, you can successfully yield good quality cannabis. We are here to teach you how to set up and optimize your grow room in the winter time.

When growing cannabis in winter, even an indoor garden is at the mercy of the elements. Cold, dry air and dropping temperatures can create problems with relative humidity and light intensity. But that doesn’t mean that growing in winter is impossible. Actually, with the right conditions, an indoor garden can perform just as well in winter as it does in the summertime.

It is true that growing in the winter takes a little more attention and a little more TLC. With the right advice and the right frame of mind, you can successfully grow all year round. That is what we are here to help you do!

How to maintain grow room temperature in winter

Temperature is one of the most important concerns when growing in the winter. Optimal daytime temperature for cannabis is 24-30°C (75-86°F), and optimal night-time temperatures falling in the range of 18-22°C (64-72°F).

As a grower, you want to avoid temperatures outside of the prescribed range but you also want to avoid huge discrepancies between day and night temperatures. Growth rate is severely affected by inconsistent temperature changes as much as by an incorrect temperature bracket.

As well as this, if there is too great a discrepancy between daytime and night-time temperatures in the first 2-3 weeks of the flowering period (during which time plants ‘stretch’ noticeably), very widely-spaced internodes will result. Conversely, keeping the discrepancy as small as possible throughout this time reduces the space between nodes.

A temperature gap of 2-4°C (3.6-7.2°F) is ideal for the first 2-3 weeks of flowering. A gap of no more than 10°C (18°F) should be maintained for the rest of the flowering period.

If you are an old-school cannabis grower, then you probably love growing in the winter. That is because last decade’s HID (high-intensity discharge lightning) technology emits alot of heat. And if you are using them in the summer time, then you need to pay through the roof for air conditioning. But in winter, HID lights can keep your grow room at the optimal temperature.

With that being said, a temperature drop when the lights are turned off is something to think about. To mitigate this, winter growers use their lights during the night time and use daytime as the lights off period. This lets a grower take advantage of warmer temperatures during the day.

While daytime temperatures are higher, they are not always high enough to maintain the plants’ required ‘night-time’ temperatures of 18-22°C (64-72°F). If temperature is consistently dropping below this range when lights are off, it is advisable to use central heating or an electric heater to maintain adequate temperatures.

A digital thermostat will come in handy here to automatically control the heater according to the ambient temperature. If using cold lights such as LEDs, heaters may be required round-the-clock.

Controlling humidity of cannabis grown in winter

Mould is one of the biggest threats to your cannabis garden during the winter. In the winter, there is a tendency for low temperatures to increase relative humidity (RH) to a point of danger for your plants. Not only do cannabis plants detest high levels of relative humidity, but it also makes them a breeding ground for mould and fungi. Low temperatures can create issues in maintaining relative humidity.

Essentially, the volume of water in the air continues to condense as the temperature drops. And if you have ever grown cannabis before, you know that this can open up a proverbial can of worms (or better yet, mould) all of your plants.

The obvious way out of this problem is to keep temperatures at the optimum level, whether by using lights or by using central heating. If the problem is extremely hard to contain, then it may be necessary to use a dehumidifier.

It is also highly recommended that winter growers purchase a device called a hygrometer. This device can test the relative humidity of your soil as well as your grow room. It is essential to regularly measure the relative humidity in order to stay on top of it and avoid huge spikes or drops in the concentration of water in the air.

In many areas, winter is actually the driest time of the year, as well as being the coldest. If you are not facing issues of relative humidity, then cold dry air will present problems of its own in the grow room. If air is taken in from outside at a temperature of 10°C and an RH of 50%, it will contain water vapour at 4.7g/m³. If this air is heated to 25°C without the addition of extra moisture, its RH will drop to around 20%, which is far too low for healthy cannabis plants to grow.

In the growroom, a moist growing medium along with transpiration will generally raise levels of water vapour in the air. However, relative humidity should remain consistently between 40% and 60%.

Other things to consider when growing in winter

Temperature and humidity are the main issues that winter-time growers will have to deal with. Lighting is usually not an issue as plants are typically grown under HID lights.

Having said that, some hobby growers might still be eager to utilise as much natural sunlight as possible, such as growing on a windowsill. The problem with this is that light intensity or simply the amount of sunlight hours may be insufficient for growth. Each area will vary in its wintertime habits, and each grower should make choices accordingly.

Some clever growers will use extra lighting during winter only, to ensure that their plants have enough light to grow. While plants will usually not achieve the yields and qualities achieved in more favourable times of the year, there are plenty of smart hobby gardeners out there that will ensure their supply remains steady even in the harshest times of the year by following this principle.

Greenhouse growers are similarly affected by the reduction in daylight hours during winter, and unlike those growing on their windowsill at home, additional lighting may attract unwanted attention.

However, some adventurous greenhouse growers will add the supplementary lighting and then make sure that the greenhouse is covered so that light does not escape when it is dark outside. Thick, heavy blackout curtains or Mylar sheeting can do an excellent job here. Then, all that remains is to heat the greenhouse sufficiently and provide adequate airflow, and growing throughout the winter should become possible.

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Consider growing winter-appropriate strains

Every grower understands the temptation of growing their favourite strains throughout the winter, even if those strains aren’t really appropriate for winter growing. If you can let go of that temptation and choose winter-appropriate strains, you might be able to avoid some of the difficulties in growing over a snowy winter.

Let’s look at autoflowering strains as an example. In as little as 8 weeks from germination of the seed, you can have a ready-to-harvest cannabis plant. This means that a grower can avoid growing throughout the harshest part of the winter and maximize their growing opportunity.

Any strain that contains ruderalis genes is also more likely to make it through a winter. Ruderalis is tougher and hardier than more common strains. It also isn’t photoperiod dependent, meaning it will flower when it’s ready rather than as a response to a change in light hours. It can bloom within 30 days of planting.

Growing in winter might mean doing some additional planning in advance to prevent the demise of your plants. But that doesn’t make it impossible. After a couple of seasons growing weed in a snowy winter, it should start to feel like second nature.

You don’t need to put down your garden shears and your green thumb just because it has snowing outside. You just need to take the weed garden indoors!

The pros and cons of growing marijuana in a greenhouse through the winter

Most experienced Canadian cultivators know a thing or two about growing marijuana outdoors, but until recently, a move so bold as openly growing or smoking weed would have been shunned and lead to arrest or fines. Now, due to legislation that came into effect on October 17, 2019, every household may grow up to four cannabis plants at any given time.

Though it’s not quite what so many cannabis enthusiasts had hoped for, it’s more than enough to grow a personal supply, especially with the assistance of an appropriate space that is dedicated to the cause. Unfortunately, with an ever-expanding population and shrinking living spaces, most do not have the luxury of an extra bedroom that can be converted into a grow room, and one solution to that issue is a greenhouse.

If you are interested in the prospect of growing marijuana in a greenhouse, then there are more things to consider than you might think, as it isn’t all sunshine and roses once the setup is erected. There is plenty of hard work and financial investment required to make it really work in the winter, so it is important to consider all the pros and cons before delving in and getting started on building one of your own.


These are a handful of the most popular reasons why so many growers choose to utilize a greenhouse in the winter.

1. Optimal climate control
Every marijuana plant will thrive best once it is provided with the ideal environment in which to do so, and two of the most important factors in this equation are the temperature and humidity levels. You will need a hot and almost sticky humid space for the highest growth rate and cannabinoid content, and a greenhouse can give you all of that and more with the addition of a small heater and a good seal to keep the cold out.

2. A warm retreat
Not everyone enjoys more tropical climates, but those that do will absolutely love having a greenhouse to relax in with a warm cup of coffee, a good book, and a marijuana plant or two at your side for company. Toss on some summertime jams, enjoy smoking weed in the heat, and in no time, you will feel like you’ve finally made it on vacation without ever having to leave your backyard.

3. Enjoy growing marijuana all year long
Growing marijuana outdoors typically requires that the cultivator pay special attention to the time of year in order to get seedlings strong and ready for rooting in time. In Canada, the average growing season begins around the same time as veggies, which is the end of May or beginning of June, and most have crops harvested by October to avoid potential damage from ice-cold frost that can come in at any time.

Those with a greenhouse don’t have to abide by such restrictive seasons that can be unpredictable at best, and since no one wants to lose a whole crop to good old mother nature, many cultivators opt for the protection of an outdoor greenhouse. That way, they can start whenever they want and harvest as it suits them rather than out of haste.

4. Expands on preexisting space
Since most houses these days are designed to save space, they are being made smaller and smaller each year. Though it was once commonplace to have a guest bedroom, storage room, and office on top of the necessary bedrooms, most people are barely making things work with one bedroom to every one or two people that live in the household.

Luckily, even those who reside in townhouses have at least a small outdoor space that could hold a greenhouse the size of a small shed. It might not be big enough to throw a party in or to house a whole veggie garden, but it would be the perfect size for growing four or less cannabis plants.

5. Keeps pests and diseases away
The marijuana plant is a hardy species that can hold a lot, but pests and water-borne diseases can plague and kill off an entire crop quite quickly. Most regions experience a massive decline in the local bug population once the temperatures begin to drop, but not all areas get cool enough to eliminate this fear entirely. A greenhouse can offer protection from both all throughout the year, in the summer and wintertime.


Most good things in life come at a cost, and while the price to be paid for using a greenhouse for growing marijuana isn’t too high, it is one that should be considered so that you don’t come across any unpleasant surprises while partway through this journey.

1. Costly to build
Greenhouses intended for winter-use are built using heavy-duty materials that can cost a fair amount no matter how you go about it. Luckily, some of the cost can be mitigated by finding a used greenhouse online, or by opting for self-assembly rather than hiring a company to do the job for you, but to save money, it would be best to shop smart which takes time and effort.

2. Requires an open outdoor space
Growing marijuana outdoors is a dream for consumers who live in multiple-unit dwellings like apartment buildings with no backyard. Though it is unfortunate, there is no way for a greenhouse to work indoors as it needs even exposure to the light, and even if it could, it would be taking up valuable space and serve a minimal purpose, so, unfortunately, a greenhouse is only a viable option for those who have access to a secured outdoor space.

3. Energy consuming
Most assume that a greenhouse does most of the work for you and that investing in one means skipping over some of the other more costly investments that are required to grow cannabis plants successfully indoors. Unfortunately, most don’t realize that to avoid mold-growth you will need to maintain an air exchange system, and some even find it necessary to add additional heating elements to ensure a consistent temperature. So, it is important to know that even though a greenhouse is relatively energy-efficient, it will make the hydro bills spike a bit more than usual.

4. Breaks easily and expensive to repair
Most people who choose greenhouses for growing marijuana select a style that includes glass panes, which is an effective material for amplifying the heat from that natural UV rays of the sun, however it does have a certain weakness which means that it’s more likely to break if a branch, rock, or moving shelf hits it too hard. Once the seal from the outdoors is broken, the greenhouse effect will no longer be strong enough to maintain the same temperatures, so keeping money on hand for essential repairs just in case is absolutely necessary.

5. Not safe for anyone with heat-sensitive medical conditions
Heat and humidity can be relaxing and even sedating, but it isn’t always safe for people with high blood pressure or any other medical condition that may be exacerbated by intense environment. If you suffer from a pre-existing medical condition, be sure to discuss the possibility of spending large amounts of time in a greenhouse with your healthcare provider.

Weed strains that thrive in colder temperatures

Indica strains are better equipped to handle the difference in the environmental conditions such as temperature changes or humidity.

If you are interested in the prospect of growing marijuana in a greenhouse, then there are more things to consider than you might think.