Verbena question
 

I planted 4 Verbena plants in my garden but the first time my sprinkler
system came on the red flowers got knocked off. The sprinklers are connected
to a drip and they emit a very gentle spray. Do I pinch back the Verbena for
more flowering like other flowers? And are they that fragile that I need to
run a regular emitter to the base? Thank you, Steve T.