Does latitude effect flowering times for different outdoor strains?

[Phillybonker]

Lets say a particular landrace strain takes 8 weeks to finish flowering outdoors at it's native location of 29° N, would it take longer to finish flowering outdoors at 38° S or the same amount of time?

Another example - A hybrid strain takes 9 weeks to finish flowering outdoors at 50° N where it was breed, would it take less time to finishing flowering at 38° S or the same amount of time?

 

[Phytoplankton]

Interesting question, not sure of the answer. I googled it and didn’t find the answer to that question, but what I found seems to point toward genetics winning more often than environmental lighting. First, you should try and match, as closely as is possible, the strain to the landrace latitude. While mismatched latitudes will grow, they probably won’t grow optimally, and may not affect flowering length. Maybe someone else has more insight.

 

[Old man farms]

Very good question, in my experience latitude and longitude do play a role in your grow it may require more or less of certain nutes so pay attention to foliage, other then that it may hermie on ya if so do a FIM and load nitro in your soil and one last thing it will look a little different then the strain usually would appear as far as flowering times should stay close to whatever the strain goes watch your Trichomes is always the best bet

 

[HopHead]

Like the others have said, interesting question. The length of daylight will be different at different latitudes and at different times of the year. The closer to the equator the less of a difference. Daylight hours may vary from 11 hrs in the winter to 13 hrs in the summer. However, the closer to the poles the greater the difference. In winter there's no daylight and in summer there's no darkness at the north pole. "Land of the midnight sun" The opposite for the south pole.

Your question centers around flowering time finishing and I don't know the answer. The different latitude locations would affect when flowering begins but I suspect genetics determine the length of flowering.

 

[cbdhemp808]

Lets say a particular landrace strain takes 8 weeks to finish flowering outdoors at it's native location of 29° N, would it take longer to finish flowering outdoors at 38° S or the same amount of time?

Hey Philly, I'll take a crack at this.

First, the photoperiod cycle of the location is what will determine when flowering starts, assuming you are not growing in a greenhouse and using lighting to control flowering.

Second, let's assume a summer growing season, with harvest in the fall. So, at the North latitudes, the season begins on the summer solstice, June 21. At the South latitudes, the season begins on Dec. 22.

Third – and this is a big one – I'm going to assume that the number of days in the flowering phase is the same at either location, and that the answer to "how long does it take to finish flowering" is mainly dependent on the starting date of the flowering phase. This is a big assumption, and I don't know if it's the correct assumption. The opposite assumption would be that the number of days in the flowering phase is mainly dependent on the solar exposure during the flowering phase, which is less the farther away from the equator that you are – both photosynthesis and temperature factor in here.

Let's also assume that the landrace or hybrid is NOT an equatorial sativa. Those can take 12+ hours of darkness to start flowering. This is important, because the date of the start of flowering will dictate the date of harvest, and in addition, the solar exposure and temperature during the flowering period, up to harvest time. So, let's assume the plants start flowering when night length equals 10.5 hours.

So, the given strain will be grown in the summer season, let's say starting on June 21 for the North latitude, and Dec 22 for the South latitude. (The answer to your question – how long will they take to finish flowering, at either latitude – lies in when they will start flowering at either latitude.)

The only difference then is the distance from the equator. To simplify, we could talk about 29°N vs. 38°N... a difference of 9 degrees. Let's pick a couple cities in North America... Bay City, TX, is at 29° N, and Lexington, KY, is at 38° N. Now, what does the photoperiod look like late in the season? The plants will start flowering right around Aug. 1 at Bay City, and around Aug. 20 at Lexington – almost a 3 week difference in the start of flowering. (I just picked two major cities in the U.S. to find and compare the photoperiod cycle at those locations. Let's assume for simplicity that the climate – i.e. temperature range, number of sunny days, etc. – are the same.)

So, continuing with the example... when do we harvest? For the 8-week plant at Bay City, 29° N, harvest would be around Sep 26. The day and night length will be roughly equal at that time: 12 hours. For the plant at Lexington, 38° N, harvest would be 3 weeks later, around Oct 17. At that time, the night length in Lexington is 12.8 hours, and the day length, 11.2 hours.

We have a baseline conclusion now, and that is: The plant grown farther from the equator has a later start time for flowering, and hence a later finish time. Now we can also consider the nuance that the plant grown farther from the equator experiences shorter day length, for the whole flowering period, than the plant grown closer to the equator. This mean overall less solar exposure, meaning less photosynthesis. How would that effect the duration of the flowering period?

Maybe some indoor growers could chime in here. What happens with your expected harvest time if you run your lights 12/12 (on/off) vs. 11/13? My guess... not a big difference.

Going back to Bay City vs. Lexington, I'm going to guess that there's very little difference in expected harvest date due to the nuance of day length being 12 hours vs. 11.2 hours by harvest time.

Another example - A hybrid strain takes 9 weeks to finish flowering outdoors at 50° N where it was breed, would it take less time to finishing flowering at 38° S or the same amount of time?

We can apply the same analysis to 38° vs. 50°, which is a 12° difference (instead of 9°). This time we can look at Lexington and a city 12° farther north... I found Regina, Saskatchewan, Canada, at around 50° N. Let's say the plant was bred in Regina. The plant will start flowering at Lexington around Aug. 20, while in Regina, around Sept. 1 – i.e. 12 days later. For the 9-week plant at Regina, 50° N, harvest would be around Nov. 3. The day length at that time is around 9.65 hours, and night length 14.35 hours. For the plant in Lexington, 38° N, harvest would be 12 days earlier, around Oct. 22. At that time, the night length in Lexington is around 13 hours, and the day length around 11 hours.

The difference in solar exposure at the end of flowering is even greater for the 38° vs. 50° analysis – 1.35 hours. Compare to 0.8 hours for 29° vs. 38°. This implies overall less solar exposure during flowering for the 50° N location.

My main concern about 50° N is cold temperatures during late flowering. It would certainly be prohibitively cold at Regina, Saskatchewan, for an outdoor grow not in a greenhouse. I don't know about other locations at 50° N. Maybe at sea level near the ocean it would be warm enough.

@Wastei, can you shed any light on this, especially my 3rd paragraph?

 

[Phillybonker]

Hey Philly, I'll take a crack at this.

First, the photoperiod cycle of the location is what will determine when flowering starts, assuming you are not growing in a greenhouse and using lighting to control flowering.

Second, let's assume a summer growing season, with harvest in the fall. So, at the North latitudes, the season begins on the summer solstice, June 21. At the South latitudes, the season begins on Dec. 22.

Third – and this is a big one – I'm going to assume that the number of days in the flowering phase is the same at either location, and that the answer to "how long does it take to finish flowering" is mainly dependent on the starting date of the flowering phase. This is a big assumption, and I don't know if it's the correct assumption. The opposite assumption would be that the number of days in the flowering phase is mainly dependent on the solar exposure during the flowering phase, which is less the farther away from the equator that you are – both photosynthesis and temperature factor in here.

Let's also assume that the landrace or hybrid is NOT an equatorial sativa. Those can take 12+ hours of darkness to start flowering. This is important, because the date of the start of flowering will dictate the date of harvest, and in addition, the solar exposure and temperature during the flowering period, up to harvest time. So, let's assume the plants start flowering when night length equals 10.5 hours.

So, the given strain will be grown in the summer season, let's say starting on June 21 for the North latitude, and Dec 22 for the South latitude. (The answer to your question – how long will they take to finish flowering, at either latitude – lies in when they will start flowering at either latitude.)

The only difference then is the distance from the equator. To simplify, we could talk about 29°N vs. 38°N... a difference of 9 degrees. Let's pick a couple cities in North America... Bay City, TX, is at 29° N, and Lexington, KY, is at 38° N. Now, what does the photoperiod look like late in the season? The plants will start flowering right around Aug. 1 at Bay City, and around Aug. 20 at Lexington – almost a 3 week difference in the start of flowering. (I just picked two major cities in the U.S. to find and compare the photoperiod cycle at those locations. Let's assume for simplicity that the climate – i.e. temperature range, number of sunny days, etc. – are the same.)

So, continuing with the example... when do we harvest? For the 8-week plant at Bay City, 29° N, harvest would be around Sep 26. The day and night length will be roughly equal at that time: 12 hours. For the plant at Lexington, 38° N, harvest would be 3 weeks later, around Oct 17. At that time, the night length in Lexington is 12.8 hours, and the day length, 11.2 hours.

We have a baseline conclusion now, and that is: The plant grown farther from the equator has a later start time for flowering, and hence a later finish time. Now we can also consider the nuance that the plant grown farther from the equator experiences shorter day length, for the whole flowering period, than the plant grown closer to the equator. This mean overall less solar exposure, meaning less photosynthesis. How would that effect the duration of the flowering period?

Maybe some indoor growers could chime in here. What happens with your expected harvest time if you run your lights 12/12 (on/off) vs. 11/13? My guess... not a big difference.

Going back to Bay City vs. Lexington, I'm going to guess that there's very little difference in expected harvest date due to the nuance of day length being 12 hours vs. 11.2 hours by harvest time.



We can apply the same analysis to 38° vs. 50°, which is a 12° difference (instead of 9°). This time we can look at Lexington and a city 12° farther north... I found Regina, Saskatchewan, Canada, at around 50° N. Let's say the plant was bred in Regina. The plant will start flowering at Lexington around Aug. 20, while in Regina, around Sept. 1 – i.e. 12 days later. For the 9-week plant at Regina, 50° N, harvest would be around Nov. 3. The day length at that time is around 9.65 hours, and night length 14.35 hours. For the plant in Lexington, 38° N, harvest would be 12 days earlier, around Oct. 22. At that time, the night length in Lexington is around 13 hours, and the day length around 11 hours.

The difference in solar exposure at the end of flowering is even greater for the 38° vs. 50° analysis – 1.35 hours. Compare to 0.8 hours for 29° vs. 38°. This implies overall less solar exposure during flowering for the 50° N location.

My main concern about 50° N is cold temperatures during late flowering. It would certainly be prohibitively cold at Regina, Saskatchewan, for an outdoor grow not in a greenhouse. I don't know about other locations at 50° N. Maybe at sea level near the ocean it would be warm enough.

@Wastei, can you shed any light on this, especially my 3rd paragraph?

Some seeds that I will be getting come from 50° N and that is why I ask my question. Thanks for the very in-depth answer.

 

[cbdhemp808]

Some seeds that I will be getting come from 50° N and that is why I ask my question. Thanks for the very in-depth answer.

Thanks for posting the question – it flushed out some murky areas in my understanding of flowering time as relates to different geographic locations and climates.

I think you'll have no problem growing a 50° N strain at 38° S. My guess is that it will start flowering sooner, and be ready to harvest sooner, than at 50° N. It may finish in less than 9 weeks, due to more solar exposure at 38° S. You can use this website to determine the best time to plant the seeds and when the plants will start flowering:

SunCalc sun position- und sun phases calculator

Application for determining the course of the sun at a desired time and place with interactive map.

suncalc.org

happy growing!