The Tucson area has been hit with two hard freezes in the past three years; hard enough that many species of plants once thought to be fairly cold tolerant are now relegated to the list of not hardy here.
If you are looking at frost damaged plants in your landscaping and wonder when you can remove dead plant parts, the answer depends of the plant.
If the damaged plants are species normally winter dormant in the Tucson and Green Valley area, it is okay to cut out the dead stalks, but leave the leaves around the base to protect the root zone from getting hit in the next cold snap. This includes Lantana, Bougainvillea, Red Bird of Paradise, and many winter dormant vines such as Queen’s Wreath, Passion Vine and Yuca Vine.
Frost damage on other types of plants, such as citrus, hopbush, oleander and cassia (aka Senna) is permanent and often deadly damage, especially when the plants are young. The true answer here it to replace these plants with cold hardy species, but if you want to keep them, do not prune off seemingly dead plant parts until late spring. Waiting until at least May, and in some cases longer, gives the plant time to recover. It is important to wait to prune, as if you prune too soon you will trigger the plant to generate new growth at the wrong time, risking another freeze back. Additionally, pruning too soon means you might be taking off green wood, which may have sprouted new leaves had you left it attached.