solve the rotation problem with magnetic flight stands?
Lastly, some of the plastic plants and flowers that you can buy come with stiff plastic stems, often with wires inside.
In these cases, it's easy to make some generic bases ahead of time...
...and then when you have the bits, just poke some holes...
...flock, seal...
...and presto!
(These bases have rounded bottoms from my "paper towel" experiment mentioned earlier...)