I like hashy's answer.
Yeah, tehy are just normal plants with XX sex chromosomes. So you'll get 50% male and 50% female when crossed with an XY male plant.
.....X....Y
X XX XY
X XX XY
2 of each.. this is called a punnet square. you line up all the alleles on 2 sides of table, then cross reference them to find the ratio of outcomes for the genetic trait, in this case, gender.