First Early Sexing Method
If you've been growing the same strain and all the seeds were started at the same time, then you may notice that some plants are taller than others: the smaller plants tend to be female and the taller ones tend to be male. You can separate these plants into two sections in order to see how good your guesswork was when you do definitively identify sex. The other thing to note is that male plants generally start to pre-flower before females. If you have taller plants that are producing new growths before the smaller ones then the taller plants are probably male.
Second Early Sexing Method
A good way to identify plant sex at an early date is to examine the calyx* with the aid of a very fine magnifying glass. If the calyx is raised on a small, short stem then it's probably a male. If the calyx isn't raised on a small short stem then it's probably a female.
Third Early Sexing Method
'Force-flowering' is probably the best early-sexing method. To force-flower a cannabis plant, simply take a cutting and place it in a cup of water or a cloning medium, such as rockwool. Expose the cutting to 12 hours of light followed by 12 hours of total darkness. The cutting should flower and display its sex — however the plant must be mature enough to present its sex. An immature plant will not show sex because initial calyx development is not photoperiod-related. Plants normally mature around the forth week of vegetative growth because sex is not genetically determined until the third week of growth.This also applies to 'feminized seeds,' which can, and often do, turn out to be male.** If your plants are exhibiting calyx development, then this is a suitable method of determining the plant's sex.
These methods are NOT 100 percent accurate. Later in this Chapter we will explain how to definitively identify the sex of your marijuana plant.