Does Persephone make plants grow when she orgasms? I got the impression from the asphodel with her first wet dream and how the pomegranate grove seemed to thrive the more sex she and Hades had.

Yes with an if, no with a but.

In the world above, yes definitely.

Persephone creates flowers conscientiously and with strong emotion. (There was also that time where she and Aidon got together after not seeing each other for three months right after she dealt with Sisyphus.)

As far as the pomegranate grove is concerned, the grove matured in step with their relationship maturing and growing closer. It had to exist before Elysion could be created, and Elysion could only be created by way of the hieros gamos. So that was beyond hers and Aidoneus’s particular control.