Put some gloves on, because this will get messy, and run the infested stem between your thumb and forefinger, squashing the aphids as you go.
A bucket of soapy water next to you to wash the bug juice off your gloves is a good idea as you squish. It is messy and time-consuming but because 99% of the aphids will be flightless you can do some serious damage to their numbers.
If, however, you don’t get them all they will soon be back so this is not a one-time and done job.
Hose Them Off
One easy method of trying to keep aphids off your treasured flowers is to spray them off with a high-powered hose.
This should knock the aphids off and also kill a few at the same time. This is a fairly easy method and doesn’t harm the plant at all as long as it is established enough – don’t do this with young plants!