Palms are often associated with tropical beaches. While the majority of palm species are sensitive to cold, certain varieties possess an unexpected resilience that allows them to thrive in temperate climates. A palm’s survival depends on a few factors, including the species’ natural hardiness, the duration of the cold event, and the lowest temperature reached. Understanding these elements is fundamental for successfully growing palms outside of consistently warm regions.
How Cold Affects Palm Physiology
Palms are monocots, growing from a single, centralized point known as the apical meristem or “spear.” This structure is located deep within the crown. Unlike dicot trees, palms do not possess a protective layer of bark to shield this growth center. The absence of a vascular cambium means that if the meristem is destroyed, the palm cannot generate new growth and will die.
Freezing temperatures damage palms primarily by causing the water within the plant’s cells to crystallize and expand, rupturing the cell walls. This damage is most severe in the softest tissue, the emerging spear leaf and the meristem. Even temperatures above freezing, known as chilling injury, can cause discoloration and necrosis in highly tropical species if the cold is prolonged. If the meristem tissue freezes and dies, it creates an entry point for opportunistic fungi and bacteria, leading to a secondary infection called “bud rot” or “spear rot.”
Identifying Cold-Hardy Palm Varieties
Selecting the appropriate species is the most important factor for growing palms in cooler regions, and hardiness is measured by the lowest temperature a palm can tolerate. The Needle Palm (Rhapidophyllum hystrix) is the most cold-tolerant species, capable of surviving brief dips to approximately -10°F, making it suitable for USDA Hardiness Zone 6b. This palm is trunkless, growing in dense clumps with its growing point protected close to the ground.
The Windmill Palm (Trachycarpus fortunei) can typically withstand temperatures down to around 5°F to 10°F. This species is known for its fibrous, hairy trunk that offers insulation to the growing point, allowing cultivation in Zone 7b. The Pindo Palm (Butia capitata) is the hardiest of the feather-leaved palms, tolerating temperatures as low as 5°F and growing well in Zone 7b.
The Dwarf Palmetto (Sabal minor) survives down to approximately 0°F for short periods, often without a visible trunk above ground. The European Fan Palm (Chamaerops humilis) tolerates temperatures down to 10°F and is well-suited for Zone 8. Selecting a palm rated for a zone colder than the local area provides a buffer against unexpected, severe weather events.
Strategies for Protecting Palms from Freezing
Proactive measures taken before a cold snap can increase a palm’s chance of survival. Deep watering the soil a day or two before a freeze is important because moist soil retains more heat than dry soil, providing a warmer microclimate around the roots. Applying a thick layer of organic mulch (four to six inches deep) over the root zone protects the shallow root system from freezing solid.
For shorter-term protection during extreme cold, use physical barriers to shield the vulnerable growing point. Tying the fronds together into an upright bundle protects the central spear from direct exposure to wind and ice. The trunk and bundled fronds should then be wrapped with a breathable insulating material like burlap or a specialized frost cloth.
If temperatures fall well below the palm’s tolerance, temporary heat sources can be used under the wrapping. Strands of C9 incandescent holiday lights, which produce heat, can be strung around the trunk and crown before wrapping. Alternatively, build a frame around the palm and cover it with plastic to create a makeshift greenhouse. Ensure the plastic does not touch the fronds, and ventilate the structure during warm, sunny days.
Assessing and Treating Cold Damage
After a severe freeze, patience is required before taking any drastic action, as the full extent of the damage may not be immediately apparent. The first sign of cold injury is the browning or blackening of the outer fronds, which should be trimmed only after the threat of subsequent freezes has ended. Leaves with remaining green tissue must be left in place, as they continue to photosynthesize and provide food for recovery.
The “spear pull” test checks the health of the growing point by pulling the central, emerging frond. If the spear slides out easily and the base is mushy and emits a foul odor, the meristem has died or is rotting from a secondary infection. If the spear pulls out, immediately treat the exposed cavity with a broad-spectrum fungicide, such as a copper-based product, to prevent rot from spreading.
The fungicide application should be repeated after about ten days to protect the growing point from pathogens. Recovery can be slow, sometimes taking an entire growing season for new, healthy fronds to emerge. The appearance of new growth, even if initially small, confirms the palm has survived the cold event.