COLD SENSITIVITY OF BROMELIADS

Dale W. Jenkins

Sarasota Bromeliad Society

Growing tropical bromeliads outdoors in a subtropical environment results in problems from winter freezes. This is of special importance in Florida, Mississippi, Louisiana, Texas and California in the United States and in Australia and New Zealand.

In general, bromeliads which come from the higher latitudes such as southern United States and southern South America and from higher elevations on mountains in tropical regions are the most cold hardy. Those bromeliads growing at lower tropical regions such as the Amazon basin are the most cold sensitive. This does not always hold true.

Bromeliad growers in the subtropical areas have published much information especially in the 1950 to 1970 period on the cold hardiness and cold sensitivity of plants exposed to cold winter freezes. This includes data on survival, degree of damage, and mortality at certain subfreezing temperatures. Many reports merely state that plants are cold hardy (which can be interpreted to mean survival at 20 to 32 degrees F.) without reporting the temperature or the degree of damage if any. These reports were used only with corroborating evidence.

A compilation is presented on the available published and unpublished information on bromeliad cold hardiness at about 20 degrees and 26 to 28 degrees F. and cold sensitivity at about 32 degrees. Some species, varieties and cultivars are found in more than one category based on the data available. While these data are quite valuable, they are subject to scientific evaluation and interpretation. The temperature measurements may come from weather bureau or other measurements some distance from the bromeliads. Walker (1976) reported that using mini-max thermometers there was a 10 degree F. variation in the microclimates of his small garden. An important variable is the amount and kind of overhead coverage , protection from cold winds and the duration of freezes.

Jenkins (1994) has grown many types of tropical fruit trees in Sarasota for 20 years studying cold hardiness and cold sensitivity using mini-max thermometers. Young fruit trees and young growth of mature trees are most sensitive to freezes. Development of cold hardening by exposure to cool or cold temperatures before heavy freezes increase survival.

For bromeliads there is some evidence that new pups or offsets are less sensitive to freezing than the mature or mother plants which may be in an old age state of decline after flowering. However, for certain species, younger plants are more sensitive than mature ones. There is evidence for some species that exposure of bromeliads to cool periods before a heavy freeze may not develop cold hardening but may result in decline of physiological fitness. There is more evidence that growing certain bromeliads hard, by exposure to cool weather results in cold hardening and increased survival to sudden freezes. A theory supporting this is that cool temperatures induce starches to convert to sugar producing antifreeze cold hardening.

An area of controversy is whether bromeliads, especially those with wells as in Neoregelia, should have the wells filled with water during a freeze. One grower reports that leaving frozen ice in the wells at 23 degrees resulted in death, while those with the ice shaken out survived. Another theory is that by not watering, the plants dry out and go into a dormant state resulting in more cold hardiness. Often plants with thicker or more leathery leaves and succulents with thick leaves such as Dyckia and Hechtia are more resistant to freezing, but exceptions occur. Fisher (1963) published a list of 52 different bromeliads that survived 20 degrees F. for 6 to 8 hours with little or no serious damage. This was in several cities in the Orlando, Florida area. It was implied that all of the plants were covered by overhead protection such as tree branches. He recommended that all plants with wells should be filled with water before freezes.

There does not appear to be any scientific studies with bromeliads (except for pineapples) of the exact temperature of the plants microclimate. Therefore, nearly all of the measurements published should be considered as approximations of the cold hardiness and cold sensitivity of bromeliads. There is a need for accurate scientific studies to supply answers to some of these questions. Considering that bromeliads are tropical plants they show quite a degree of cold hardiness. Even when the plant is apparently dead, suckers or pups often emerge later.

The data compiled for cold hardiness and cold sensitivity are presented in tabular form instead of separate lists since these are not mutually exclusive. A single species may be found in several categories. All numbers are degrees F.

The categories used are as follows:

H 20 = hardy with survival with little or no damage at 20 degrees Fahrenheit (-6.7 Celsius) for several hours.

H 26-28 = hardy with survival and with little or no damage at 26 to 28 degrees Fahrenheit (-3.3 to -2.2 Celsius) for several hours.

D 26-28 = death or severe damage at 26 to 28 degrees Fahrenheit (-3.3 to -2.2 Celsius) for several hours.

S 32 = cold sensitive with death or severe damage at 32 degrees Fahrenheit ( 0 Celsius) for several hours.

LITERATURE CITED

Anderson, L. 1981. Growing bromeliads in an unhospitable climate.
Bromeliad Soc. 21(3): 126-128.

Beadle, D.A. 1998. The Bromeliad Cultivar Registry. The Bromeliad Society International. Pp. 423

Bidlingmayer, M. 1980. Bromeliads in a Vero Beach garden. J.Bromeliad Soc. 30(2): 74-75.

Cargo Report. Periodical report by Tropiflora, Sarasota, FL.

Converse, H.H., Jr. 1981. Low temperature tolerances and cold hardiness in bromeliads.
J. Bromeliad Soc. 21(3): 115-118.

Dimmitt, M.A. 1992. Bromeliads. A Cultural Manual. The Bromeliad Society, Inc. pp.44.

Dorr, K. 1976. Southern California. J. Bromeliad Soc. 26(3): 101-102.

Drysdale, W. 1963. Let’s talk about the weather. From a Sunset Garden.
Bromeliad Soc. Bull. 12(4): 86-87

Ensign, E.R. 1958. Bromeliads in the Central Florida freeze.
Bromeliad Soc. Bull. 8(l): 7.

Fisher, W.B. 1963. Let’s talk about the weather. From a Florida garden.
Bromeliad Soc. Bull. 13(4): 87-88.

Fisher, W.B. 1963. Hardy bromeliad checklist.
Bromeliad Soc. Bull. 13(6): 142.

Foster, M.B. 1958. Cold tolerance of some terrestrial bromeliads.
Bromeliad Soc. Bull. 8: 10-11.

Groves, G. 1997. Lecture at the BSCF, Mar. 1977. 2pp.

Hall, J. 1958. How the native bromeliads took the cold in Florida,
Bromeliad Soc. Bull. 8(1): 6-7.

Hatrick, W. 1958. Bromeliads in the Huntington Botanical Gardens.
Bromeliad Soc. Bull. 3(1): 3-6.

Hobbs, M.H. 1958. Frost damage in the New Orleans area.
Bromeliad Soc. Bull. 8(1): 9.

Hyning, D.V. 1958. What the freeze did to my bromeliads.
Bromeliad Soc. Bull. 8(1): 8.

Jenkins, D.W. 1994. Fruit and nut plants for the Sarasota area.
Tropical Fruit News. Sept. 1994: 10-12.

Kimnach, M. 1972. Terrestrial bromeliads at the Huntington
Botanical Gardens, J. Bromeliad Soc. 22(4): 82-85.

Knoblock, E. 1958. Notes from Mary Plantation, on the Mississippi River.
Bromeliad Soc. Bull. 8(1): 9.

Knoblock, E. 1972. The bromeliads of Mary Plantation.
Bromeliad Soc. Bull. 22(3): 53-59.

Lee, H.A. 1981. Bromeliad growing amid changing weather conditions.
Bromeliad Soc. 31(6): 245-247, 254.

Nally, J. 1958. Bromeliad damage at Gotha, Florida.
Bromeliad Soc. Bull. 8(1): 3-4.

Padilla, V. 1951. Some observations on the cold tolerance of bromeliads.
Bromeliad Soc. Bull. 1(4): 35-36.

Simmons, G. 1976. Central Florida. J. Bromeliad Soc. 26(2): 77-78.

Taylor, R.K. 1979. "Frost Resistant". J. Bromeliad Soc. 29(4): 171.

Walker, L. 1976. Southern California. J. Bromeliad Soc. 26(4): 163-166.

Williams, B.E. 1990. Growing Bromeliads. By the Bromeliad Society of Australia, Inc. Kangaroo Press. Pp. 112.

Wurthmann, E. J. 1984. Brazilian Vrieseas prove to be freeze stalwarts.
Bromeliad Soc. 34(6): 252-254.

ACKNOWLEDGMENTS

I wish to express appreciation to Wally Berg and Harry Luther for updating the taxonomy, to Dennis Cathcart for data on cold hardiness for 25 species, and for helpful review comments by Witt Merrin, Kenneth Stokes, Tom Wolfe and my wife Joanne Jenkins.

I also thank the Selby Botanical Gardens for the use of their excellent botanical library.