Female/Male Ratios

Throughout my first 4 grows, I've enjoyed a high ratio of female to male plants. Out of a total of 16 plants that made it to the flowering stage, 11 have been female, with 2 grows being 100% female. Early on in my first grow, I posed the following question -

Is sex determined environmentally or genetically, both? I've always wondered how that works with cannabis plants.

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Here is an interesting response I received -

GreatLife4All;1865331 said:

This is actually an interesting topic.

Genetically - MJ is pre-programmed to come out 60% female.

The actual sex is not determined until the fourth or fifth week of veg. Depending on environment - I believe you can go as high as 90% males. There was a study done by Dutch Seeds - it is still available on the web - which included this result:

Of the 5 above-mentioned environmental factors the first three are the most practical:

Level of nitrogen and potassium of the seedbed: A heightening of the standard level of nitrogen makes for more female cannabis plants originating from the weed seeds. A lowering of the nitrogen level shows more male cannabis plants. A heightening of the level of potassium tends to show more male marijuana plants, while a lowering of the potassium level shows more female marijuana plants. A combination of a higher nitrogen level for the period of a week or two and a lowering of the potassium level is recommended.

Humidity and moistness of the seedbed: a higher humidity makes for an increase in the number of female cannabis plants from weed seed, a lowering for an increase in male cannabis plants. The same is valid for the moistness of the seedbed.

Level of temperatures: lower temperatures make for a larger number of female marijuana plants, higher temperatures for more male marijuana plants.

Colour of light: more blue light makes for female cannabis plants from seed, more red light makes for more male cannabis plants.

Hours of daylight: few hours of daylight (e.g. 14 hours) makes for more female individuals, a long day (e.g. 18 hours) makes for more male cannabis plants.
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While it is quite subjective, I've also noticed some correlations between the above and my grows.

Employing GLR is reducing the hours of light my plants receive to just 13 hours a day.

My worst grow for female/male ratio was my third grow (2/4) which vegetated during last summer. Due to heat concerns I did not employ any CFL sidelighting which supplies the vast majority of blue light during vegetating.

My last grow's ratio was 3/0 and was kept below 85° for the entire grow. My second grow's ratio was 2/0 and was also kept below 85°.

There probably isn't much behind this given my low sample numbers, nonetheless, it piqued my interest noticing the correlations in preparation for my next grow.