Good morning Bonnie and thank you for contacting the UNH Extension Infoline.

Wait until the plant has gone dormant, late winter of early spring. The plant blooms on new wood. Prune out any dead branches, otherwise, just a slight pruning to keep the desired plant shape is all the pruning it should need. Doing pruning in late winter or early spring will prevent the removal of new flower buds. Stem tip pruning, in early spring, will encourage flowering.

Dead, diseased, or damaged branches can be pruned off at any time.

Yes , the seeds may be used to grow additional plants. The plant will self sow and produce populations of seedlings in the vicinity of the parent plant.  The seeds
require no special treatment to germinate. Store the seeds in a cool dark location for the winter. Place seeds in an envelope or in an airtight jar in the refrigerator. You can plant the seeds directly in the soil after the danger of frost has  passed. Or start them indoors like you would flower and vegetable seeds. Harden off transplants before moving outdoors with other transplants.

I hope this answered your questions and please contact us for any additional information.