Hardy palms are any of the species of palm (Arecaceae) that are able to withstand brief periods of colder temperatures and even occasional snowfall. A few palms are native to higher elevations of south Asia, and a few can tolerate hard freezes with little or no damage. Many of these "hardy " species can be cultivated in warm temperate climates.
The hardiest species are found in the generaRhapidophyllum, Sabal, and Trachycarpus. Members of these and other genera are sometimes grown in areas where they are not truly hardy, overwintering with the aid of various kinds of artificial protection.
The minimum temperature a palm can sustain depends on a variety of factors, such as humidity, size and age of the palm, daytime high temperatures, or the length of time the temperature is at the minimum. −5 °C (23 °F) for several days will do far more damage to a palm than an overnight low of −8 °C (18 °F) for an hour or so.
Windmill Palms (Trachycarpus fortunei, T. takil) – the best known cold-hardy palms, these tough species are native to eastern China and the Himalaya mountains. Hardy to about 0 F/-18 C. Although not growing so far north (to about 31°N) as the Needle Palm, they do grow at high altitudes where temperatures are cool. It is also tolerant of low summer temperatures. Mature Trachycarpus trees have been successfully grown as far north as 58°N in northern Scotland. Mature specimens can also be found in most parts of Ireland, England, Vancouver, Vancouver Island, Canada, eastern Asia (Japan, China, South Korea), and in parts of Australia and New Zealand. In the United States Trachycarpus is grown as far north as Seattle on the Pacific coast and Long Island/coastal New Jersey on the Atlantic Coast.
Mediterranean Fan Palm (Chamaerops humilis) – The only palm native to southern Europe, and very drought-tolerant. Hardy to −12 °C (10 °F), but does prefer hot summers. Despite the fact that this palm is less hardy than many palms listed here, it has the northernmost native habitat because of the mild Mediterranean climate. It is found in abundance across most of southwestern Europe and northwestern Africa. It is a very slow-growing plant. The blue form of the species, native to high elevations of the Atlas Mountains, has recently been introduced into the trade and early reports indicate that it may be 5 °C (41 °F) or more degrees hardier than the green form.
Needle Palm (Rhapidophyllum hystrix) – This clustering and usually trunkless palm is native to the subtropical southeastern United States, from central Florida to Georgia, Mississippi, South Carolina and Alabama in the United States. It is considered hardy to USDA Hardiness Zone 6b and is cultivated along the West Coast of the USA from California to Seattle and along the East Coast from Florida to southern Connecticut. They have proven hardy in the Tennessee valley region and up into the lower Ohio Valley. During the winter, it can tolerate temperatures as low as −23 °C (−10 °F) for short time periods. The needle palm is very slow-growing and rarely reaches heights of over 1 m (3 ft 3 in). There are documented specimens that have been growing in White County, Tennessee, since the early part of the 1960s, as well as United States National Arboretum in the Asia Valley section, in Washington D.C., that are at 3 m (9.8 ft) in height. A Needle Palm has been growing since 2003 in the St. Louis suburb of Alton, Illinois.
Mazari Palm (Nannorrhops richtiana) – This palm, native to the dry, mountainous terrains of northern Pakistan, Afghanistan, and surrounding regions, is also thought to be extremely cold hardy (perhaps to about −20 °C or −4 °F), though also requiring hot summers and dry soils. However, due to its limited availability in cultivation, not much is known about this palm. Mazari Palm is not easy to grow, perfect drainage and full sun are required for this palm to survive. This palm will not tolerate wet freezes.
Saw Palmetto (Serenoa repens) - These palms are native to the southeastern United States, most commonly along the Atlantic and Gulf Coastal plains, but also as far inland as southern Arkansas, this bushy palm is hardy to about −15 °C (5 °F). This bushy palm grows in abundance within wetlands and subtropical grasslands of central and northern Florida. Extract from Saw Palmetto is often used to treat problems with the prostate.
Sabal palms (palmettos; 13 species) – These palms are native to the southeastern United States, Central America, and the Caribbean. The Cabbage Palmetto (Sabal palmetto), the state tree of both Florida and South Carolina, is very common on the southeast coast of the United States. The species is considered hardy to USDA Hardiness Zone 8, and may survive short periods of temperatures as low as −14 °C (7 °F). The Dwarf Palmetto (S. minor) is the hardiest species in the genus. The cultivar 'McCurtain' is considered the hardiest, to USDA zone 6b, like the needle palm. It can tolerate short periods of temperatures as low as −22 °C (−8 °F). Sabal minor, a dwarf palmetto that it forms a subterranean trunk, is the most cold hardy, able to take short periods with near −18 °C (0 °F) temperatures. The Mexican Palmetto (Sabal mexicana) is a close relative of the Cabbage Palmetto, native to southern Texas and northern Mexico.
Washingtonia palms (Washingtonia filifera, W. robusta) – These palms are native to southern California and northwest Mexico, growing as high as 30 m (98 ft) in their native habitat. California Washingtonia (W. filifera) is hardy to −12 °C (10 °F); it prefers a dry Mediterranean climate, though it still grows in areas with humid subtropical climates like Brisbane, Sydney, Houston, and New Orleans. It is sometimes grown in containers, or planted as short-term specimens in areas where it is not quite hardy. Mexican Washingtonia (W. robusta) is somewhat less hardy, native to northern Mexico (Baja California Peninsula). It has a more robust trunk and stiffer leaves than W. filifera, and is hardy to −10 °C (14 °F).
Chilean Wine Palm (Jubaea chilensis) – A contender for the hardiest pinnate-leaved palm, it is hardy to about −12 °C (10 °F) and has been cultivated successfully as far north as Seattle, Washington, Vancouver, British Columbia, and LondonEngland. This palm does not perform well in hot, humid climates.
Butia Palm or Jelly Palm / Pindo Palm (Butia capitata) – With Jubaea, possibly the hardiest known pinnate-leaved palm. Butia capitata, also known as Jelly Palm, is a palm native to Argentina, Brazil and Uruguay. This palm grows up to 6 m (20 ft), exceptionally 8 m (26 ft), in a slow but steady manner. It is easily identifiable with beautiful feather palm pinnate leaves that arch inwards towards a thick stout trunk. Butia capitata is notable as one of the hardiest feather palms, tolerating temperatures down to about −10 °C (14 °F); it is widely cultivated in warm temperate regions. It is commonly grown on the East Coast of the United States as far north as Virginia Beach, Virginia and Portland and Seattle on the West coast. It thrives in humid subtropical climates. This tree is commonly known as the "jelly palm" because of the sticky, edible, date like fruit it produces, which is used in many South American countries to make jelly.
Chamaedorea microspadix and Chamaedorea radicalis – the hardiest known species in the genus Chamaedorea. Both species come from Mexico and are considered stem hardy to about −11 °C (12 °F), although they will lose their leaves at temperatures below about −6 °C (21 °F).
Canary Island Date Palm (Phoenix canariensis) – This species is hardy to about −10 °C (14 °F), and is grown as far north as the south of England (50°N), producing viable seed (in Southsea, Hampshire). In North America. mature specimens can be found as far north as Gold Beach, Oregon (42.5º N)on the West Coast and Myrtle Beach, South Carolina (34.1 N) on the East Coast. This palm is one of the most commonly grown palms in the world. Well adapted to low humidity and little watering, this palm is used as an ornamental in both Mediterranean climates and desert climates. In more humid climates, these trees will often be seen with sword ferns sprouting just beneath the crown.
Cretan Date Palm (Phoenix theophrasti) – Another species of Phoenix which may show similar frost tolerance, native to Crete and southwest Turkey, but has not been adequately tested.
Date Palm (Phoenix dactylifera) – This relative of the Canary Island date palm, and producer of the edible date, is also hardy to about −10 °C (14 °F), but does not tolerate very wet areas. This palm is one of the staple plants of the Middle East for its versatility and edible fruit.
Mule Palm (× Butiagrus nabonnandii) – Hardy to about −10 °C (14 °F). Manmade hybrid between the Butia palm and Queen palm. One of the hardiest feather palms. It combines the hardiness of the Butia palm with the fast-growing, tropical fronds of the Queen palm. Mature specimens are quite rare due to the difficulty in producing this palm and the characteristics and cold tolerance of the palm is variable with each specimen. Many of them resemble coconut palms.
Ceroxylon quindiuense – It is native to the ColombianAndes where it is found at 2,500–2,800 m (8,200–9,200 ft) above sea level. At this altitude it tolerates occasional frosts for short periods of time.
In general, hardy palms can only tolerate brief periods with temperatures in the range −18 to −12 °C (0 to 10 °F). As such, this generally limits hardy palm cultivation and long term specimens to zone 7a or higher. Some hardy palms can be cultivated in areas with low temperatures slightly below this range when given wind sheltering (planted on the south side of a building). In the USA, hardy palm cultivation is generally attempted from USDA zones 6b/7a southward.
In very cold winter areas below zone 6b, cold hardy palms have been cultivated by partially (or completely) covering plants with mini-green house coverings and wraps. Some garden enthusiasts in severe cold winter areas have gone as far as heating the interiors of these winter enclosures. As such, there are occasional reports of hardy palms be cultivated in areas with severe winters with low temperatures below −18 °C (0 °F).
^"Wiki". phoenixcanariensispalm.com. 2011. Retrieved August 28, 2011. "It can be cultivated where temperatures never fall below −10 to −12 °C (14 to 10 °F) for extended periods, although it will require some protection if cold periods are longer than normal."