Know Your Plant’s Cold Tolerance

Maintaining a lush tropical landscape requires learning about your plant’s cold tolerance and the threat of chilling temperatures above freezing. When purchasing plants for your landscape, it is essential to know which USDA hardiness zone they’re growing in and each variety’s cold hardiness rating. For instance, the large geographic area of Jacksonville, Florida, is USDA Hardiness Zone 9a (20F- 25F) and borders 8a (15-20F) to the West. If the plants in your landscape and collection cannot tolerate temperatures as low as the minimum temperatures then they aren’t considered hardy for Jacksonville’s zone. View USDA Hardiness zones from around the country and find yours by zip code at USDA Agricultural Research Service.

Avoid planting your most cold-sensitive plants with northern exposure and consider other more hardy plantings around them as wind blocks if you must. It’s common knowledge that houseplants and tropicals won’t survive freezing temperatures. However, there is less appreciation for the fact that chilling temperatures within specific ranges above freezing can also result in plant stress, damage, and death.

“A chilling temperature is any temperature that is cold enough to cause plant injury but not cold enough to freeze the plant,” according to the University of Florida/IFAS. “These temperatures usually range from just above 32°F to about 59°F. Chilling injury to tropical foliage plants is also dependent on the duration of exposure to a chilling temperature.”

Plants are triggered to begin acclimation or hardening in Autumn as daylight hours, and temperatures decline. Non-native plants in Jacksonville’s humid subtropical gardens face more significant fluctuations of temperature in the chilling temperature range than our neighbors in Central and South Florida’s tropical hardiness zones. While Jacksonville has an average October temperature between 81F- 66F, forecasts call for a low of 46F with 10-15mph wind on October 18, 2022. Chilling temperature plant damage can appear as wilting, yellowing, reddish-brown spots, and even mushiness.

“Tropical and subtropical crops such as ageratum, alternanthera, angelonia, basil, celosia, cleome, coleus, cosmos, lantana, pentas, poinsettia, portulaca, sweet potato vine, vinca and zinnia are classified as cold-sensitive because their development stops at a base temperature of 46 F or higher,” according to Michigan State University. “Another group of greenhouse crops is classified as cold-intermediate (or cold-temperate) crops as their development stops at moderately low temperatures of 40 to 45 F. These crops include calendula, dahlia, geranium, impatiens, lobelia, some petunia cultivars, verbena and wax begonia.” Many of our local gardens contain a mix of these plants and others with varied cold sensitivity.

Consider our Overwintering and Indoor Propagation article if you are preparing to protect your houseplants and tropicals during a cold spell and before freezing temperatures are forecast for your area. If chilling temperature damage occurs, ensure the affected plants are watered and avoid the temptation of fertilization, which can stimulate new growth and further stress the plant.

For more information on your plant’s cold tolerance how to protect your plants every season and for comprehensive solutions to your specific lawn, garden and landscaping needs contact Earth Works of Jacksonville at 904-996-0712. Earth Works operates a retail Garden Center/Plant Nursery in Jacksonville and provides landscaping, hardscaping, water features, lawn care service, lawn spraying, and drainage solutions.

Earth Works proudly serves clients in Northeast Florida, including Jacksonville, Ponte Vedra Beach, Atlantic Beach, Neptune Beach, Jacksonville Beach, Nocatee, St. Johns, Fleming Island, Orange Park, Middleburg, Green Cove Springs, Amelia Island, Fernandina, and St. Augustine.