They suffered from blight? Are you sure? ??? I thought blight only affected tomatoes and potatoes. Hollyhocks is normally hit by rust.
We left our seeds on the stems until they were dry and then took them off and put them in envelopes, you could probably take them off before but you'd need to dry them thoroughly before storing them. The best way would be to cut a stem off and tie string around it to hang it up somewhere indoors or in a shed to dry.
