Protecting and Selecting Plants for Cold Weather
By Sol Looker, UF/IFAS Extension Flagler County Horticulture Agent
Protecting plants in preparation for cold snaps during winter months can be a daunting task. Here in Flagler County we are on the edge of USDA cold hardiness zones 9A and 9B. Looking at the map, most of Flagler County falls within USDA’s zone 9A with an average annual extreme low temperature ranging of 20⁰-25⁰ F. Areas of the county between I-95 and the coast experience temperature moderation from the surrounding waters of the Atlantic Ocean and Intracoastal Waterway resulting in a slightly higher average max temperature of 25⁰-30⁰ F.
This difference of about 5 degrees can result in greater damage for some tropical plants to the west of I-95. It isn’t unusual to have a weather forecast for a “hard freeze” for interior parts of Flagler County. The current USDA cold hardiness zone map was created using average annual extreme low temperature ranging from 1976 to 2005. Click on the map for an interactive version.
Strategies for protecting plants from a freeze
There are many strategies for protecting plants from the cold. Some techniques are better suited for homeowners than others. Did you know that water gives off a small amount of heat when it freezes? That is why it is possible for large foliage and citrus producers to protect their crops from freezing temperatures by applying irrigation and forming ice on the plants.
However, there are drawbacks to this technique. One drawback is that the irrigation must remain on until temperatures return to above freezing to keep leaf tissue temperatures from dropping too low. This excessive water use is not only wasteful, but can also lead to disease issues. The other significant problem with applying irrigation for freeze protection is the amount of weight that can accumulate from ice. This often results in broken limbs and plant damage.
Covering plants can be a good strategy, but caution should be used when selecting covering material. Commercial frost blankets work well as do conventional blankets and sheets, but clear plastic that is in contact with plant material does not work well. The coverings should go all the way to the ground and be secured in place. Be sure to uncover plants when freeze danger has passed. Keeping plants wrapped up following temperatures returning to normal can do more harm than good by causing excessive heat and/or light deprivation. If a hard freeze is predicted many plants can temporarily be moved into the garage or a porch area for a night or two. Tender tropical plants in the ground that can’t be moved can be covered. For more information please see “Cold Protection of Landscape Plants”
Consider temperature tolerance when choosing plants
When purchasing cold sensitive plants consider how much time and energy you are willing to spend protecting them. Perform a little research first to see what the tolerable range is for a given plant and keep in mind how big a plant or tree might eventually become. Some cold protection can be provided by large surrounding trees and planting sites close to homes where warmer microclimates are formed.
Large tropical trees that require planting in the open sun to thrive may be risky to plant for this area. For instance, the Bizmarck palm, native to Madagascar, has been increasing in popularity due to its striking silver blue color, large size, and attractive fan shaped leaves. The Bizmarck palm is considered cold hardy down to 30⁰ F or USDA cold hardiness zone 10A, but they often survive in protected sites in zone 9B. Cold damage makes these trees highly attractive to native palmetto weevils which can infest the crown and kill the tree. Planting these palms west of I-95 in Flagler County will likely result in seasonal cold damage. This is just a single example. There are countless other plants that fall into a similar category–their maximum size is larger than can effectively be protected from cold.
Right Plant, Right Place
Many homeowners are looking to create a tropical look that is often associated with Florida landscapes. A good strategy for this climate is to add variety to your landscape by placing tropical plants in protected locations intermingled with cold hardy plants to minimize losses and negative appearance from cold weather. Look for areas in your landscape that are likely to create microclimates. Smaller plants are easier to cover with protection and potted plants can be moved temporarily. Exercise caution when purchasing large tropical specimens intended for planting in open areas. Always be sure to remember to uncover plants when temperatures return to above freezing. By following these recommendations you can have a tropical look without emptying your pocketbook to replace injured plants.