When we talk about plants in our southern landscapes that are susceptible to cold injury, consider herbaceous tropicals such as elephant ears, birds of paradise, cannas, gingers, philodendrons, etc. These plants have underground rhizomes, bulbs, corms, tubers, etc. The above ground portions of these plants are mostly soft tissue (herbaceous), and these plants are more tender than woody tropical like hibiscus, lantana, or angel trumpets. We can do some things such as covering plants, but if it gets cold enough, the above ground portions of all of the tropicals will be damaged even though we cover them. One thing that we can do to enhance protection to herbaceous tropicals with underground tubers, rhizomes, bulbs, corms etc. is to mulch well to protect the parts of these plants that are in the ground. The mulch adds insulation to protect and reduce injury so that even when the tops are killed, we can possibly save the plants. Since the ground usually doesn’t freeze during our winters, mulch provides some added protection. If both the tops and roots are injured by freezing temperatures, we may lose the plants.
Finally, woody tropical plants such as angel trumpets, hibiscus, lantana are more cold hardy than herbaceous tropical plants — as I mentioned above. All tropical can benefit from mulching to protect roots, but it’s more critical to herbaceous tropicals because they are considered soft tissue compared to woody or hard tissue tropicals.
Anytime temperatures drop into the mid-twenties or below, it is considered a “hard freeze.” If it remains this low for two hours, there will be damage, but more severe damage occurs if the hard freeze last for four, six, or eight hours. Eight hours or more are particularly damaging.