While most of us now realize that fall and winter are the best times to plant the majority of ornamental plants in our landscapes, the best time to plant palms in Louisiana is May through September. The soil is warmest this time of year, and warm soil is one of the most necessary criteria for palm root growth.
Rough handling of palm trees or severe vibrations during transport can break the tender bud, causing death many months down the road. It also is important to transplant the palm as soon as possible after removing it from the soil. Never allow the roots to become dry, although this would not be a problem with container-grown plants.
Louisiana is located in USDA hardiness zones eight and nine, and many palms will do well for us. Keep in mind though, that there is a large difference in average minimum temperatures between these zones. Climate is without a doubt the single largest limiting factor in selecting palms. Some palms will do fine in zone 9a (New Orleans, Lafayette, Lake Charles) but may be damaged in zone 8b (Alexandria, Baton Rouge) and will definitely exhibit damage in zone 8a (Shreveport, Ruston, Monroe). Reliable palms for some of these areas include:
Needle palm (Rhapidophyllum hystrix)
Probably one of the most cold-hardy palm species, the needle palm forms a clumping, understory palm with many palmate leaves. This palm is native from South Carolina to Florida and west to Mississippi. Foliage is dark green with silvery undersides. Plants are typically slow-growing and reach heights and spreads of about five feet. Needle palms need light shade and adequate moisture.
Dwarf palmetto (Sabal minor)
This palm is native to Louisiana and is found from Texas to Florida and northward to South Carolina. Mature height is six to eight feet with leaves one to three feet wide. It produces white flowers May to June. A subterranean trunk makes transplanting these palms difficult. They are also slow-growing.
Windmill palm (Trachycarpus fortunei)
Windmill palms are very popular all over Louisiana. These trees have average heights of 10 to 20 feet but can be as tall as 40 feet. Trunks are slender. Mats of dark brown, hair-like fibers coat the trunk on younger palms. Windmill palms like ample water but don’t do well in extremely moist soils or standing water. Windmill palms are relatively slow growing.
Cabbage palm (Sabal palmetto)
Florida has an abundance of cabbage, or palmetto, palms, but they are becoming increasingly popular in the central Gulf Coast. This palm can reach heights of 80 to 90 feet, but most only reach about 20 feet or so tall. Leaves are fan-shaped and three to six feet in length. These palms are adaptable to wet, poorly drained soil and have a moderate growth rate.
Saw palmetto (Serenoa repens)
This clumping palm forms thickets and is native from South Carolina southwest through Florida and westward to Louisiana. Common height is three to four feet. Saw palmetto does very well in the southern part of Louisiana. It is not common in the nursery trade.
Mediterranean fan palm (Chamaerops humilis)
This is a clumping fan palm and is slightly less hardy than the windmill palm. Mediterranean fan palms tolerate a wide range of growing conditions.
Cocos or jelly palm (Butia australis or Butia capitata)
Cocos or jelly palms (also known in the nursery trade as butia palms) are becoming better known and are the most cold-hardy of the palms with feather-shaped foliage.
A popular palm-like plant for Louisiana is the sago palm. These plants are actually not palms but cycads. The sago is a native of Japan and is hardy to 15 degrees. Its leaves are two to three feet long. They can be even larger on older plants and are divided into many narrow, needlelike segments. The primary problem with sago palms in south Louisiana is a fungal, leaf spot disease to which they are especially susceptible during periods of high humidity. Sago palms, however, are highly recommended and should be planted in the late spring and early summer, just as true palms should be.
LSU AgCenter horticulturists Severn Doughty and Dan Gill conducted an extensive survey of palms growing in south Louisiana a number of years ago. They found 14 genera comprising 21 species of palms. Of these, less than half have been found to be statistically reliable for planting due to climate limitations. So you can see that species selection is important.
Realize that many home gardeners, nursery growers and landscapers use palm species that may not be reliable for long-term performance due to cold weather. The desirable characteristics and fast growth rates of some overcome the necessity to replace them once every 10-20 years due to winter damage. Washingtonia species of palms are hardy to about 15-22 degrees and will be damaged extensively by several consecutive days of temperatures in the teens.
For palm success, select for cold hardiness. It is also important to consider vertical and horizontal space limitations. As mentioned earlier, plant in May through September for best establishment. Once established, palms should be maintained under a moderate fertilization program. During late spring and early summer, remove old leaves and flowering parts of the plants as they become unsightly.
For more information, contact Dr. Chris Robichaux, county agent/area horticulturist, St. Martin/Iberia Parishes, at 332-2181 or 369-4440.