PREDICTING HARDINESS IN PALMS
Larry R. Noblick, Ph.D., Collections Manager, Montgomery Botanical Center
and Associate Researcher, Fairchild Tropical Garden, Miami, FL
In Florida, we are fortunate to be blessed with a climate that is amenable to growing a wide variety of palms and cycads. However, the same is not true for other palm enthusiasts living in Central Florida, Texas, California, and else where in the US and in Canada. These growers struggle to keep their palms alive. This article is dedicated to the palm enthusiasts who willingly shared their experiences so that the rest of us do not continuously "repeat history". A compilation of observations made by Dent Smith (1958, 1962, 1986), Gordon Hintz (1978, 1996), Leonard Goldstein (1989), Paul Craft (1997), Kyle Campbell (1997), Eric Schmidt (1997), and others like Frederico Oste, Alan Ball (pers. comm.), Montgomery's palm horticuturalist, Laurie Danielson, and myself have resulted in Table 1, which lists all of these observations. From time to time I hope to update this Table at this website.
Some growers report different experiences with the same species of palm after a cold spell. The reasons for this involve the nature of the cold spell itself, microclimatic conditions that surround their palms, and the palms themselves. A cold spell can come on suddenly or slowly. One would think that a gradually cooling winter might give palms an opportunity to "harden off" or acclimate. But not so according to Goldstein (1989), who found that a sudden cold frost or freeze was far less devastating than an extended cold spell where temperatures never dropped to freezing. The length of time and depth of a hard freeze, wind speed, and ambient humidity can also influence how destructive a cold spell might be. That is why we see some reports of palms sustaining temperatures with little or no damage at one time, but dying at the very same temperature at another (Smith 1958, 1964). Microclimates and conditions that surround one's personal collection can spell life of death for a palm. A plant sheltered by other trees and shrubs is more likely to fair better than one that is exposed. Finally, how successfully a palm will handle cold is determined by the palm itself: its age, its height, its slight hereditary differences selected out over time by the ambient conditions of its native habitat, and the overall health of the palm specimen itself at the time of the cold spell.
Predicting cold hardiness of palms would appear to be just a matter of answering a few questions. Does it grow in the cooler north or south latitudes? Is it a high altitude palm? However, there are some tropical species that have been found to be somewhat cold hardy. But, how can one predict what a tropical palm might do during a cold spell before gambling money and resources on it?
After examining information collected on palm hardiness (Table 1), I discovered that over sixty-five percent of the species that showed no damage or very little damage at 25-26
Therefore, tropical or subtropical palms that are adapted to survive the stress of low water conditions (no matter what underlying conditions are causing it) will have a better chance of weathering a cold spell. Palms that grow in semi-arid areas, savannas, exposed sandy coastal zones, and on exposed well-drained rock faces are prime candidates for testing in colder climates, because they have the "right stuff".
These tables summarize the results of observations of the cold hardiness of palms.
CAMPBELL, K. 1997. The effects of the freeze of 1997 on palms in central and south Florida. Palm Review 17(2): 7-9.
CRAFT, P. 1997. Will Spring hurry up and get here?!!! The Broward County Palm and Cycad Society Newsletter.
GOLDSTEIN, L. 1989. Cold-weather experience in South Florida. Principes 33(2): 56-62.
HINTZ, G. 1978. Effects of the Winter of 1976-77 on certain palm species in Dallas, Texas. Principes 22(3): 94-98.
_________. 1996. Palms for South Texas gardens. Neil Sperry's Gardens, January Issue.
PETERSON, B. 1997. Best place to learn about cold hardiness in palms. Palm Review 17(2): 1, 5.
SCHMIDT, E. 1997. Pleasant and not so pleasant surprises from Leu Gardens. The Broward County Palm and Cycad Society Newsletter.
SMITH, D. 1958. Cold tolerance of the cultivated palms based on observations made at Daytona Beach, Florida during the Winter of 1957-58. Principes 2(4): 116-126.
_________. 1964. More about cold tolerance: effects of a hard freeze upon cultivated palms during December, 1962, at Daytona Beach, Florida. Principes 8(1): 26-39.
_________. 1986. U.S.D.A. hardiness zones as applied to cultivated palms, and other horticultural comments. Principes 30(1). 26-31.
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Revised May 18, 1998