Ponytail palm (Beaucarnea recurvata) is a subtropical plant that grows best in the southernmost parts of Florida and California, but it can grow anywhere as an indoor houseplant. It doesn't take well to cold weather. If possible, bring your ponytail palm indoors on frosty nights. If you can't, you can do a few things to minimize frost damage, but only if the temperature remains above 20 degrees Fahrenheit. At 18 degrees and below, the palm likely won't survive.
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Examine the foliage and bark of the ponytail palm for frost damage. Symptoms include browning or blackening of the leaves. Stems may become mushy, soft and rotten; these symptoms are caused by ruptured tissue from ice crystals that formed during a freeze.
Prune away damaged tissue with pruning shears. If leaves are still partly green and showing only a few brown spots, leave them on the tree. Any photosynthesis that occurs, even on damaged leaves, helps the palm recover.
Spray the remaining ponytail palm foliage with a fungicide that contains copper, following the packaging instructions carefully. Repeat the application in 10 days. The fungicide serves as a preventive measure to keep pathogens from attacking the damaged tissue while it recovers.
Fertilize the ponytail palm after the second fungicide spraying with a fertilizer formulated for palm trees. Follow package instructions for the correct proportion for the size and age of the tree. Repeat the application once a month through the growing season, ceasing in early fall.
Watch for signs of recovery and new growth. Don't be alarmed if new leaves are distorted in the first year after frost damage. Keep the ponytail palm well watered as it goes into the following winter to give it the best chance of survival.
Keep a young ponytail palm indoors as an attractive houseplant. Move it outdoors when it grows too large for the house.
Watch the ponytail palm foliage at the height of summer for signs of crown collapse. This usually indicates frost damage was too severe in the trunk of the palm for it to survive.