Do NOT cut them off at the base with a weed wacker or anything else. Trim off the dead blooms, and allow them to die back naturally to the base. then remove the dead foliage and care for them depending on local weather and growing conditions. year around gardens, leave in the ground, cold areas you may want to dig up for winter.
contact your local extension office and speak to a locally trained MASTER GARDENER for the best way to do it for you own area.