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.

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.

  • Disclaimer:
    Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.

Comments

30 thoughts on “How to Grow Cannabis in Winter”

  1. Thank you for the info, it must be frustrating to keep telling the same people you can’t “Blog Answer”. Even when you provide the link to the forum for any questions they have,

    1. Scarlet Palmer - Sensi Seeds

      Hi Derek,

      Thanks for your kind words! I do wish we could simply give grow advice in the comments section, but unfortunately that’s not a service we can offer right now. Also the forum is no longer active, although it is still there to be used as an archive, so I’ve had to modify my replies. Now I say that other readers will often offer advice if they can, so the comments section can serve the same basic purpose as the forum. I hope you continue to enjoy the blog,

      With best wishes,

      Scarlet

  2. winter in Greece is surprisingly very cold and quite snowy. definitely a forbidden time for outdoors, at least until late february, up to late november, when you can try with autoflowers. photoperiods are traditionally placed to the strict period 25/3 – 28/10 (symbolically the 2 national days, but actually the beginning of spring and end of autumn).

    indoors winter is the ideal season since you avoid the extremely hot summer period, october to march is the best period. growing indoors april to september can prove much hotter than outdoors, without the aid of an a/c. you can always control the temperature at winter, utilising the house’s own heating vs an open window to the fresh air. this cannot happen without a/c in summer, which by the way can give your plants literally a cold.

  3. Very interesting article. I have grown cannabis outdoors during the winter while temps were down to 40 degrees Fahrenheit. they were not looking good as they turned purple and didn’t grow much. But when spring/summer hit and temps were up to 100 degrees they took off turning dark green and growing crazy. So I think you can at least keep them alive during the winter as long as temps don’t get to the freezing level.

  4. Hi iv been growing a plant in my window and she is just love n it never thought it would be so easy

  5. Helpful info! Thank you! The summer here gets 10c at night so I see why there’s a long stretch between nodes. Great find I know what I need to do ????????

    1. Scarlet Palmer - Sensi Seeds

      Hi Maria,

      Thank you for your comment ? Unfortunately, for legal reasons we cannot respond to grow questions on the blog, but we do have the Sensi Seeds Forum where you can ask a thriving community of gardening fans for advice, share your experiences, and see if your question has already been covered. I hope this helps.

      With best wishes

      Scarlet

    1. Scarlet Palmer - Sensi Seeds

      Hi Someone,

      Actually it’s a tiny oasis of calm in the exhilarating cannabis rollercoaster that is my job. And it only takes a couple of seconds. 😉

      With best wishes

      Scarlet

  6. I’ve germanated 3 plants put them in the window sill….no results…however it’s only been 3 days ….and i also live in the great state of Ky…lol….it is snowing …not much sun as u can imagine…I’m starting to get worried ..didn’t happen I’m the summer months..of course…..what should I do. I have more germanated seeds dont won’t to loose them too.

    1. Scarlet Palmer - Sensi Seeds

      Hi Bruce,

      Thank you for your comment ? Unfortunately we cannot respond to grow questions on the blog, but we do have the Sensi Seeds Forum where you can ask a thriving community of gardening fans for advice, share your experiences, and see if your question has already been covered. I hope this helps.

      With best wishes

      Scarlet

    2. Buy a grow tent and a grow light I suggest Sun Blaster and they are relatively cheap it’ll work the best for germinating…

  7. So your info is about how to grow in the winter but u can’t answer anyone about a topic you started??? Confused maybe you shouldn’t put up topics u can’t reply answers on said subject about???

    1. Scarlet Palmer - Sensi Seeds

      Hi Brad,

      Thanks for your comment. I can understand the confusion because on the surface, it does not seem to make sense that we publish articles about growing and then have to deflect all questions about it to the forum. The reason for this is that cultivating cannabis is against the law in most places, and tolerated within strict boundaries in a few. Even in the Netherlands, one is only allowed to grow up to five plants and they have to be outdoors. It is also against the law to incite others to commit a crime, and to assist or facilitate them in doing so. This puts us in a delicate legal situation. We are a Dutch company and have to abide by EU laws. Therefore, all the articles on the blog are for entertainment purposes, and must not be used to commit or facilitate crime. Answering questions or giving advice about illegal activities would mean we are breaking the law.

      At the same time, we strive to produce interesting articles which people will find entertaining and relevant. We also host the Sensi Seeds forum, but we are not responsible for its content as it is all user-generated.

      I hope this clears it up for you 🙂

      With best wishes,

      Scarlet

      1. Omg!! I was just thinking the same, exact thing!!! Wtf??
        If you have questions, please refer to my last dzn answers.
        I can’t answer that…blah, blah, blah.
        Yesss, why is this blog here?
        Heyyy Brad, maybe? Maybe they will answer this… …. why is this blog here????!!!!

      2. Scarlet Palmer - Sensi Seeds

        Hi Cid,

        Did you actually read my reply to Brad? The blog is here because “we strive to produce interesting articles which people will find entertaining and relevant”, whilst at the same time, having to stay within a strict set of boundaries which are legally imposed, not our own choice. It is not an ideal situation, I agree, and it is indeed frustrating having to constantly direct people to the forum rather than being able to answer questions directly. However, the combination of blog and forum is the best solution we currently have available to us.

        Additionally, when it comes to questions about growing, there are so many other people who can (and do) weigh in that comment threads in a blog format become unwieldy and confusing. A forum format is far more suited to this kind of answer threading. Brad’s comment that “u can’t answer anyone about a topic you started??? Confused maybe you shouldn’t put up topics u can’t reply answers on said subject about???” suggests that he thinks this is a forum – we did not “start a topic”, we posted an article. Comments are welcome, as is feedback, but there is a big difference between the two platforms (blog and forum) in terms of both author and commenter response. To avoid disappointment, they should not be confused.

        With best wishes,

        Scarlet

  8. Hey what’s up, I bought 10 Bubblegum seeds still have 5 left, 3 didn’t take but 2 did. The first one I grew outside starting in July and in temperatures for France. Sadly to say this one turned out to be a male, but I let it grow anyway love the leave style. The second one is growing now but inside in a small cabinet. The problem is the cold and out of eye for my small children when they are here.
    I have made everything need to grow, 2 cabins one in a bedroom 80 cm high and another in the attic 180 cm high. Lighting with CFL 400 watt total, in 6500 for veg. and 2700 for flowering, also ventilation, feeding and timer electric. The attic is the perfect place undercover from my kids, but the cold. The cabin is not insulated for now it depends on the price, that I am looking into this week.
    What I’d like to know is information about your ” Sensi Skunk Automatic Seeds” they are marked as a cold plant. What is their support for temperature range ? How high do they grow about ? And the time around they take before harvest ?
    I have decided not to grow a lot of plants at one time, just enough for a continue the flow. Hash does relive my medical problems like cannabis, and it is very hard to find in the area I live. If you could give me an answer quickly, I would have no problem to purchases this strain either today or Monday. I’ll be waiting to see if you get to answer quickly, if not I’ll be waiting patiently for your answer.
    Thanks and later, Tommie

    1. Scarlet Palmer - Sensi Seeds

      Hello Tommie,

      Thank you for your comment and your interest in the Sensi Skunk Automatic ?. Unfortunately we cannot respond to grow questions on the blog, but we do have the Sensi Seeds Forum where you can ask a thriving community of gardening fans for advice, share your experiences, and see if your question has already been covered. Additionally, we have this grow report for the Sensi Skunk Automatic which will provide you with further information on the questions you ask. I hope this helps, and good luck with your project!

      With best wishes

      Scarlet

  9. William hill

    I am doing my first winter greenhouse crop. The lighting in the winter is not sufficient to bud out my plants so can I use flourescent lighting or must I use sodium lights?

    1. Scarlet Palmer - Sensi Seeds

      Hi William,

      Thank you for your comment ? Unfortunately we cannot respond to grow questions on the blog, but we do have the Sensi Seeds Forum where you can ask a thriving community of gardening fans for advice, share your experiences, and see if your question has already been covered. I hope this helps.

      With best wishes

      Scarlet

  10. If I start growing 1st day of winter in green house and remove the green house at 1st day of spring . When will I harvest flower . I wanna know if warm weather at april or may harm the flower or not ?
    And can I harvest 2times (at may and at September )?

    1. Scarlet Palmer - Sensi Seeds

      Hi David,

      Thank you for your comment ? Unfortunately we cannot respond to grow questions on the blog, but we do have the Sensi Seeds Forum where you can ask a thriving community of gardening fans for advice, share your experiences, and see if your question has already been covered. I hope this helps.

      With best wishes

      Scarlet

  11. Germinating mid October putting out in polytunnel what should I expect? Seeds used are early skunk femenised automatic mold resistant. Should I use the old fashioned hot bed method?

  12. which type of seeds can be used in winter ?

    If possible i prefeer Feminized and Regulars, not Automatic.

    awaiting for your reply as soon as possible,

    greetings,

    paolo

    1. I use a Kush strain in my winter grow. They are hearty in the colder weather. Plus there life cycle is shorter than a sativa happy growing! ✌?️

  13. Thanks for this info it is very helpful, i live in a cold climate and its regularly below frezing point, i will keep this info in mind.

    Many thanks.

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    Sensi Seeds

    The Sensi Seeds Editorial team has been built throughout our more than 30 years of existence. Our writers and editors include botanists, medical and legal experts as well as renown activists the world over including Lester Grinspoon, Micha Knodt, Robert Connell Clarke, Maurice Veldman, Sebastian Maríncolo, James Burton and Seshata.
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