by Seshata on 30/12/2014 | Cultivation

How to grow cannabis in winter

Winter People living in regions of the planet with cold winters need to take certain steps to ensure success when growing cannabis. However, once certain factors are taken into account, many growers find that winter growing is much less problematic than growing in the height of summer! This guide assumes cultivation is done indoors.


How to maintain grow room temperature in winter

Temperature is the obvious consideration when growing in winter. Cannabis requires daytime temperatures of 24-30°C (75-86°F), and night-time temperatures of 18-22°C (64-72°F). If night-time temperatures drop below 16°C (61°F), growth rate will be severely affected.

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 using hot lights, the heat they generate is often sufficient to keep plants at an adequate temperature, but the temperature drop when they are switched off may be significant. To mitigate this, winter growers will usually keep lights on during the night and off in the daytime, as daytime temperatures are usually considerably higher than at night.

How to grow cannabis in winter

While daytime temperatures are higher, they are often not 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

If temperatures are too low, problems with high relative humidity may result. As air temperature decreases, the volume of water that can remain as vapour also decreases—for example at 25°C, air at 100% relative humidity contains 23g of water vapour per cubic metre, while at 15°C the same volume of air can hold just 12.8g/m³. At 25°C and 60% relative humidity (RH), the air holds 13.8g/m³; if temperatures drop to 20°C, the RH will increase to 80%, and if they go as low as 15°C, the water vapour content will exceed the air’s capacity to hold it and will rapidly condense.

If the water vapour content of air at a given temperature exceeds its water vapour capacity, condensation will inevitably occur; this is often a problem in winter, particularly when the temperature drops at night. Cold, damp conditions are the perfect breeding ground for moulds such as powdery mildew and botrytis, particularly when condensation is allowed to remain for prolonged periods. Use of a good dehumidifier should resolve this problem, as well as maintaining slightly higher temperatures where possible.

How to grow cannabis in winter

In many areas, winter is actually the driest time of the year, as well as being the coldest. Cold, dry air can present its own problems when brought into 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?cannabis to grow healthily. In the growroom, the presence of moist growing medium along with water released through transpiration will generally raise levels of water vapour in the air, but if RH consistently remains below the recommended 40-60%, use of a humidifier may be necessary.

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 high-intensity discharge (HID) lighting. However, many hobby growers will utilise natural sunlight where possible to grow cannabis (e.g. on a windowsill), and will find that both the hours of daylight and the light intensity of the available sunlight during winter will be insufficient for growth.

How to grow cannabis in winter

Some clever growers will use supplementary 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, supplementary lighting may attract undue attention. However, some intrepid 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.

Comment Section

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Michael

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.

02/01/2015

kevin

Out door growing marijuana in the winter

07/09/2015

Paolo

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

09/10/2015

Kronic T

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! ✌?️

14/08/2017

cliff uk

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?

15/10/2015

Stefanie

Hi cliff uk,
thank you for your comment. For growing questions, I'd like to refer you to the Sensi Forum: http://forum.sensiseeds.com/.

Best -
Stefanie

16/10/2015

david

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 )?

30/09/2016

Scarlet Palmer

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

03/10/2016

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?

14/10/2016

Scarlet Palmer

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

14/10/2016

Tommie

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

02/12/2016

Scarlet Palmer

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

05/12/2016

Brad

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???

09/12/2016

Scarlet Palmer

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

09/12/2016

Bruce

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.

06/01/2017

Scarlet Palmer

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

10/01/2017

Brandon

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

26/07/2018

Someone

Hehe must be boring to post same answer over n over:)

13/01/2017

Scarlet Palmer

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

13/01/2017

maria

i need to know for outgrowing winter time for greece pls

31/05/2017

Scarlet Palmer

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

31/05/2017

Kronic T

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 ????????

14/08/2017

Luke

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

25/12/2017

Ken Smith

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.

29/07/2018

Kostas

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.

30/08/2018

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