Tucson, Arizona, Gardening Tips After a Freeze

Vines and Small Shrubs

• Smaller plants have less mass to resist freezing weather and may be killed down to ground level by the cold. An example is lantana cultivars (Lantana camara), hardy to U.S. Department of Agriculture plant hardiness zones 8 through 11. Lantana dies back when temperatures reach 28 degrees F. Prune lantana to the ground once danger of frost has passed and wait for warm weather, when the plants regrow from the roots. Similarly, wait to prune frost-damaged bougainvillea (Bougainvillea spp.) until frost danger is gone, typically in March, and cut back to areas where there is new growth. Bougainvillea is hardy to USDA zones 9 through 12. Wear protective clothing when working with bougainvillea.

Trees and Shrubs

• Resist the temptation to remove obviously dead tissue on your trees and shrubs right away. Allow the damaged material to remain on the plant to help insulate the rest of the branches and roots from any other freezes that might occur. Watch for regrowth, such as buds and shoots beginning to swell and green up. Cut back the dead material to the first green bud that points in the direction that you want new growth to occur, and prune back to that point.

Cacti and Succulents

• A different approach is needed for cacti and succulents, because they are full of water-storing tissue. After freeze damage occurs, watch the damaged areas to see how much of the tissue is dead. If only small areas sustained damage, the plant can self-heal. If the damage is extensive and large parts of stems or leaves are involved, bacterial rot can occur. If rot sets in, remove infected areas with pruners or a sharp knife, sterilizing the tool between each cut with a mixture of 1 part bleach to 10 parts water. Cut the plant back to clean, white tissue and coat the wound with bleach-containing scouring powder. If no rot is present, wait until warm weather to prune away freeze damage.

Minimizing Damage

• After freezes, survey your landscape to assess where the coldest areas are. Use the experience to help you plan for the next freeze, to minimize damage. If you have to replace dead plants, choose cold-resistant plants for open landscape areas, such as native plants already adapted to Tucson. For Tucson's coldest temperatures, this corresponds to USDA zone 8. Put more tender plants in protected microclimates, such as under trees, against south-facing walls or within a covered patio. Keep the most sensitive plants in containers that can be moved inside when freezes threaten. Plan to stop fertilizing with nitrogen fertilizers past August 1, and reduce watering in the fall to slow plant growth. Get ready to cover your favorite plants that can't be moved; use appropriate cold frames to keep the covers from touching the plants.