Maybe some modeling clay? Build up a base of clay. Insert stalks.
You could also do something like set some stout wires or nails pointing up, drill some corresponding holes vertically through the bottom of the stalks, coat wires/nails with glue, slide on stalks.
The attachment doesn’t need to be particularly strong, but it does need to be secure.
You might also want to figure out some way to provide support for the upper ends of the stalks as well. Even something as simple as wiring together with fine wire, or some kind of support structure that makes sense (hell, wire one stalk diagonally between two verticals, or have a “broken” stalk act as a bridge for support).