Take a paper towel roll...
and a piece of tin foil...
Tape one side of the paper towel roll so there is no light getting threw.
Poke a tiny hole for air flow(not too big,or too much light will get threw)
slide the role over the lowest branch and rap the foil around the bottom of the role and the branch.
Prop it up with something.
You have to put it on for 12 hours a night.
For about a week or two to see the sex.
The pre flowers will show up pretty quick.
Actually I think I put it on for about 14-15 hour a day and it showed on that branch quick. One day there was a little bud growing on the branch.
I stopped puting it on the branch and left it. The branches never did anything. So eventually I cut them off.