|Picture of Yellow Bells from Arizona State University website|
A. Are you thinking they are dead because the tops die back? It is seldom that I see these plants totally die out in the winter here. They do frequently die back to within a few inches of the soil surface during the winter.
They then can be cut back to about one inch from the ground in February and they come back like gangbusters in early spring with some water and fertilizer.
|Lantana cut back in the winter to about two inches in a rock mulch in Las Vegas.|
If they are dead, I am wondering if they are not getting enough water during the winter months to keep the roots from dying out. Normally a watering schedule of about every ten days or so would be enough during the winter to keep them alive.
Otherwise try mulching over the tops of the plants with a few inches of wood mulch to keep the winter cold from damaging the roots. It is very rare these would die out in the winter here under normal landscape situations.