Can you plant flowers in fake grass?

So long as there is soil under the fake grass, you could cut holes in the medium that supports the fake grass and plant your flowers.

Watering and fertilizing the flowers, may be problematic, however, since the fake grass may not be designed to be wet.

You could be most successful planting flowers in pots and then positioning the pots on the fake grass, arranging them anew after collecting them to water and fertilize.