If it flowers, you
should be able to dissect the flowers and find out whether you got male parts or female parts there. (stamen vs. stylus) If it's not flowering, from my
experience the females tend to be less viney than the males because the male vine likes to curl around the female. Of
course, this will be hard to tell if you only have one. You could order a female, put it in the hole and if, after a year you figure you already have a female, then you can dig back the female and plant a male, or hack back a hole for a male. Or plant both in one hole the same year and prune heavily (or attempt to kill) if its a duplicate male.