How cold can day/night temperatures get before killing cannabis plants?

[Phillybonker]

In one of my grow areas the historic data on the internet suggests that in the last 1-2 weeks of bloom it can potentially get down to 1°C - 2°C at night for 2-3 nights in a row and day temperatures can be 15°C or lower for 1/3rd of the time.

My question is - How cold can day/night temperatures get before killing cannabis plants?

 

[BeanTownFan420]

I think that also depends on the hardiness of the strain. Mountain kush may fair better than tropical sativa when it's cold.

 

[Phillybonker]

I think that also depends on the hardiness of the strain. Mountain kush may fair better than tropical sativa when it's cold.

True that, the strain I'll be growing is indica dominant with strong Afghani origins.

 

[BeanTownFan420]

Sounds perfect for the situation!

 

[bluter]

cannabis stalls out below 13c. it won't die but it stops developing. it has to get above that threshold for a majority of the day to continue to mature and grow.

the important temp is root temp. air temp can be below the 13c mark, but root temp needs to stay much closer to that point. by 8c the roots die off.

 

[Lerugged]

yeah, Im with Bluter. I grow in winter in Cape Town, South Africa. It doesn't get that cold here but flowering in temps around 14C will result in very loose buds with a ton of frost and terps but the yield is really tiny. We don't get frost and have never had a plant die from being out in winter. These are landrace sativa mostly. Good luck

 

[SmokingWings]

My question is - How cold can day/night temperatures get before killing cannabis plants?

I have had plants continue to live after the nighttime lows dropped to 28F (-2C) and the next day the temperatures got up to 60F (15C) usually within a few hours. When the night time temperatures dropped to 27F and stayed there for hours then the plant leaves and younger stems died back and the plants show no signs of recovering.

As @bluter and @Lerugged bring up, there is a difference between the temperatures that will kill the plant and the temperatures that will stall out or stop growth until it becomes warm again.

 

[Phillybonker]

cannabis stalls out below 13c. it won't die but it stops developing. it has to get above that threshold for a majority of the day to continue to mature and grow.

the important temp is root temp. air temp can be below the 13c mark, but root temp needs to stay much closer to that point. by 8c the roots die off.

According to historic data it doesn't drop below 13C too often, just 2-4 days in the last 2 weeks of flowering. Thanks for letting me know that.

 

[Phillybonker]

yeah, Im with Bluter. I grow in winter in Cape Town, South Africa. It doesn't get that cold here but flowering in temps around 14C will result in very loose buds with a ton of frost and terps but the yield is really tiny. We don't get frost and have never had a plant die from being out in winter. These are landrace sativa mostly. Good luck

Am I reading this right?.....

Temps around 14C will result in very loose buds with a ton of frost (as in frosty buds?) and terps.

Loose buds are fine with me as I will also have humidity problems to deal with.

 

[Phillybonker]

I have had plants continue to live after the nighttime lows dropped to 28F (-2C) and the next day the temperatures got up to 60F (15C) usually within a few hours. When the night time temperatures dropped to 27F and stayed there for hours then the plant leaves and younger stems died back and the plants show no signs of recovering.

As @bluter and @Lerugged bring up, there is a difference between the temperatures that will kill the plant and the temperatures that will stall out or stop growth until it becomes warm again.

Thanks for sharing your experience. In my new grow area it's possible for temps to go down to -2C or maybe lower so I'll have to keep an eye on that.

 

[Lerugged]

Here are some pics of a Durban landrace. I just throw a pile of seeds and if I get anything then I get something. Fine for the vape or for extractions

 

[Sativa1970]

I played with temps to see how it effected buds during indoor winter grow. I lowered the air temp with my land strain sativas at the start of flower. 17 deg. is when bud growth really slows down. At 15 deg. it pretty much stalls. Held the plant at 15 deg. for 5 days to observe trichomes. There was no change in the plant until the root temp dropped. Once the roots dropped to 15 deg. the plant started to wilt. Raised the temp up to 18 deg. and the plant recovered and continued flowering like nothing happened. Flowering took 3 additional weeks (plus the 5 days stalled) with lower temp but yield and trichome development was not effected. I don't have any way to quantify terpene development but I could not tell any difference in smell or taste.

As long as the roots stay over 15deg. and the plant doesn't get a HARD frost it will be fine. Just takes longer to finish. A sheet tent will protect it from hard frost over night. Dark colored mulch will keep the ground warmer.

To be clear, these were equatorial plants. 23 deg is the dead of winter for these plants. So you can adjust the scale down for temperate zone plants.

 

[Phillybonker]

I played with temps to see how it effected buds during indoor winter grow. I lowered the air temp with my land strain sativas at the start of flower. 17 deg. is when bud growth really slows down. At 15 deg. it pretty much stalls. Held the plant at 15 deg. for 5 days to observe trichomes. There was no change in the plant until the root temp dropped. Once the roots dropped to 15 deg. the plant started to wilt. Raised the temp up to 18 deg. and the plant recovered and continued flowering like nothing happened. Flowering took 3 additional weeks (plus the 5 days stalled) with lower temp but yield and trichome development was not effected. I don't have any way to quantify terpene development but I could not tell any difference in smell or taste.

As long as the roots stay over 15deg. and the plant doesn't get a HARD frost it will be fine. Just takes longer to finish. A sheet tent will protect it from hard frost over night. Dark colored mulch will keep the ground warmer.

To be clear, these were equatorial plants. 23 deg is the dead of winter for these plants. So you can adjust the scale down for temperate zone plants.

Thanks for sharing the results of your experiment.