Pensacola News Journal

For: Saturday, Jan. 25, 2003

By: Daniel E. Mullins

Extension Horticulture Agent

Santa Rosa County

A Perspective on Cold Damage in the Landscape

Many gardeners, especially those new to the area, are worried about the effects of recent freezes. Numerous residents have made comments that lead me to believe that some Northwest Florida weather orientation might be helpful to transplanted gardeners.

This is Florida, but the Northwestern part is most certainly not a tropical or subtropical zone. Though we can grow a wide range of plant species, expect some to experience varying degrees of cold injury, unless only temperate zone plants are established in the landscape.

Expectations by those moving to the area appear to be excessively high. A couple of days ago someone asked why their banana plants were freezing back. And then there was the newcomer who asked if we ever get freezes here.

According to the USDA Plant Hardiness Zone Map, the southern portion of coastal counties from Pensacola to Panama City is in Zone 8b, with average minimum winter temperatures of 15 to 20 degrees Fahrenheit. The northern parts of these same counties are in Zone 8a, with average minimum temperatures of 10 to 15 degrees.

Native and long term residents to the area all have their weather stories. I remember the winter of ’89 and ’90 when the temperature at one location in Pace was 5 degrees F. I also remember a snow in late March several years ago.

The point is, we are in a unique zone – at the extreme southern border of the temperate zone and not quite subtropical. Our location has its advantages and disadvantages. One advantage is that we can grow many of the temperate zone plants and also many of the subtropicals. A disadvantage is that though the subtropicals love our spring and summer weather, they can be damaged to varying degrees depending upon the severity of winter weather and the species being grown.

Many gardeners, including myself, take a laid back approach to the possibility of cold injury. The colorful subtropical and tropical perennials such as hibiscus, pentas, shrimp plant and salvia provide so many benefits for 8 to 9 months during the warm season that we are willing to take our chances. If some freeze - so what! They can be replaced, or the opportunity is provided to try a new kind of plant the following spring.

That said, there are some practices that help to prevent or at least reduce the incidence of cold injury to landscape plants. First, make sure that plants are not moisture stressed when a freeze is expected. Plants in dry soil are much more likely to suffer from low temperatures than those growing in moist soil. Provide the landscape with a good watering one to two days before extremely low temperatures are predicted to arrive.

Allow the plants to go dormant by withholding high nitrogen fertilizers during late summer and early fall. If fertilization is done after September, use a product that is low in nitrogen and relatively high in potassium.

The covering of landscape plants for cold protection is popular, but is not always practical. Covering should be limited to only the most valuable specimens that would be difficult to replace.

Proper covering requires that a plant be completely draped and that the material extend all the way to the ground on all sides so that ground heat is trapped. This means covering plants during late afternoon and then removing the covering the next morning as soon as temperature rises above freezing.

Obviously, covering plants correctly during our typical brief freezes requires a commitment in time and effort. It would not be unusual to repeat the procedure of covering and uncovering plants a dozen times during the winter once the procedure is begun. To my way of thinking, it takes a very special plant to justify that much work.

Fortunately, most landscape plants are amazingly resilient. With only a few exceptions, by late spring we are usually surprised at how well the perennials and shrubs survived the winter.