We have some Bidens Golden Eye which are supposed to grow to a height
of 20-30 cm and be "superb cascading from baskets". Unfortunately some
of these have reached a height of 40-50 cm and none show any interest
the concept of trailing.

If I leave them will they eventually fall over and trail? Should I cut
them back because they are growing too tall or will that just remove
the growing and flowering tip? Is there any way to persuade these
trailers that they are trailers?

TIA

JB