A Florida Freeze: Preparing for the Freeze

A Florida Freeze

A Florida Freeze is upon us. Every once in a while, Nassau County will freeze. Many of our landscape plants will not be affected by any cold snaps, but we do have some plants that may be susceptible to frost or freeze damage. Preparing our landscapes for frosts and freezes will require proactive steps, but also knowledge for landscape recovery if your plants experience frost damage. This blog will cover three basic principles:

Preparing for a Freeze
Identifying Freeze Damage
Freeze Damage Recovery

Different Types of Freezes

Frosts, freeze warnings, and hard freezes (not including chill hours) all characterize different temperatures in the landscape.

Frosts – Temperatures drop below 36 degrees Fahrenheit.
Freeze Warning – 80% chance of dropping below 32 degrees Fahrenheit.
Hard Freeze – When temperatures drop below 28 degrees Fahrenheit.

When we discuss freezes impacting our landscapes, we describe two types of freezes: radiational and advective.

Radiational Freezes – Frost occurs on plants as heat escapes the plants’ surfaces (radiant heat) and they are cooler than the atmosphere. Ice will form if there is moisture in the air. Plant damage from radiational freeze may be minimized by reducing heat loss from plants.
Advective Freezes – Freezes resulting from cold, arctic air masses that cause sudden drops in temperatures.

Preparing for a Freeze

When we view our local weather forecast, we sometimes see a frost/freeze. Preparing our landscapes for frosts and freezes can help in protecting our landscapes from potential freeze damage.

To best prepare our landscapes is by following the Florida-Friendly Landscaping Program’s first principle, “Right Plant, Right Place.” Depending on where you live in Nassau County, we are within USDA Hardiness Zone 8b or 9a. The hardiness zones are based on the average low temperature for your area. 8b range is 15 – 20 degrees Fahrenheit and 9a is 20 – 25 degrees Fahrenheit. Selecting plants suitable for our USDA Hardiness zone will ensure your plants will experience little to no damage to our landscape plant material.

Although, some things like citrus, veggies gardens, container plants, or other specialty plants benefit from freeze protection.

Covering Plants

Plants may be covered with fabrics such as cloth sheets, quilts, plastics, or specialty frost cloths from the store. Drape cloths over the plants and shrubs, and try to let the cloths reach the ground. Do not tie off the covers. Radiant heat from the ground gets trapped under the cloth. If we tie off the covers we’re unable to get the benefit of the radiant heat. Make ghosts, not lollipops. Also, if possible, especially for perennials and veggies, try to avoid direct contact with the plants. The fabrics could cause damage to the plants or pull heat away – making them more susceptible to damage. If you using plastic covers, be sure you remove them as soon as possible. Excessive heat could cause damage to the plants. Additionally, plastics easily pull heat away from the plant when in direct contact. Additionally, providing a light (non-LED) under each cover helps provide additional heat under the covers.

Photos showing proper way to protect plants from a Florida Freeze. — When properly covering trees in your landscapes, make ghosts not lollipops. Radiant heat from the ground will get trapped under the ghost, helping keep your tree warmer. Photo courtesy of Molly Jameson, UF/IFAS Extension Leon County.

Mulching Plants

Be sure your ornamental plant beds are mulched appropriately. Mulch around perennials and other shrubs helps protect against heat loss within the soils. Perennials that naturally succumb to cooler temperatures only need to have their roots protected and mulch will provide adequate protection for spring regrowth.

Irrigation & Watering

“Watering landscape plants before a freeze can help protect plants.” A well-watered landscape absorbs heat during the day and releases heat at night, but be sure you turn off your irrigation system during the freeze. Agricultural producers have irrigation systems capable of allowing them to use water/ice to protect plants – but residential irrigation systems make it difficult to effectively do so. Turning off your irrigation systems will ensure you do not have excess water in your landscape and help protect your irrigation system.

Specific Protection Recommendations

Protecting Palms – Wrap palms and palm fronds in a cloth. Be sure to protect the newest palm frond, spear leaf, and meristem (top of palm trunk), if possible. If the spear leaf dies, there’s a good chance the palm will die too. For more information about palm care, click here.
Protecting Tropical Fruit Trees and Camellias/Gardenias – Protecting the grafting site (the lowest part of the trunk where the roots begin) will ensure the tree’s survival. Covering the entire tree with a cloth will protect it or, at minimum, wrapping the bottom of the tree to protect the roots will keep the graft safe to allow for recovery later. You may also mound around the base of the tree up to 2 feet – but it’ll be important to remove this after the freeze.
Vegetables – Loosely drape a cloth over plants and secure edges with rocks or stones. Another option is to temporarily pile pine straw or mulch on top of plants to help hold heat.
Container Plants – Ideally container plants would be relocated inside. If not possible, move them away from prevailing winds, cluster container plants together, cover them with a cloth, place them under a tree canopy, or relocate them on the southeast side of a home/building.

Identifying Freeze Damage

If following “right plant, right place,” our plants will not be impacted by the freeze. But, for some plants, knowing the signs of freeze damage may help aid in recovery. Much of the damage is the result of bursting plant cells as the water within the cells freeze and expand. Leaves and foliage on plants turn brown/white/black. Older leaves on plants may appear wilted and curled downward. The cambium of plants turns brown, too. Scratching the bark on a plant typically exposes a thin layer of greenwood, but if suffering from freeze damage, the wood will appear brown. This wood will be pruned-out in the spring. Additionally, you may notice the splitting of the trunk or branches.

Freeze Damage Recovery

Recovery from freeze damage is classified by water, fertilizer, and pruning recommendations.

Watering

After a freeze passes, check the water needs of your plants. If moisture within the soil freezes, watering plants after the freeze will help thaw any ice and make moisture available to plants again. This should be avoided for citrus trees.

Fertilizer

DON’T DO IT! Despite plants being damaged, the fertilizer could initiate new growth that’s more susceptible to freeze damage. It’s best to wait until spring.

Pruning

Do not prune plants until Spring. It can be hard to tell which parts of the plants/trees were killed by the freeze and you don’t want to unintentionally remove living portions of the plant. Also, the dead/dying material on the plant could help insulate the plant during subsequent freezes. For herbaceous plants, you will notice they are wilting and brown – it would be best to remove these from the landscape because their decay could result in the development of fungal pathogens.