Not All Palms Are Created Equal

By Maureen Gilmer
DIY--Do It Yourself Network

Imagine you are a city planner and decided to line the streets of your new 1925 subdivision with palms. You choose fan palms because they don't need much water and folks immigrating from the east will buy anything with a palm on it. But a few years down the road you discover that the beautiful uniform plantings of thin trunk palms are interrupted by individuals that don't quite match. They grow slower, produce a big fat trunk and have a bad habit of hanging on to the dead fronds while the other trees' break off cleanly.

This is the scenario you'll find all over California. Streets lined with the tall, gangly Mexican fan palm (Washintonia robusta) are marred by an occasional squat California fan palm, (Washingtonia filifera) or vice versa. But there's a lot more that distinguishes these two closely related species than size.

All California fan palms in cultivation today descend from individuals found at isolated oases in southern California and Arizona. They are remnants of primordial forests that covered much of the extreme southwest. As ice ages ebbed and flowed, the climate changed forming deserts. Where it became too dry the palms died out. They remained only around rare isolated springs in the desert where ground water bubbles up to the surface.

The Cahuilla and other bands of Native Americans also lived in the oases and eked out an existence in the barren desert. They survived on mesquite beans, cactus fruit, underground tubers and palm seed. These palms became essential to their survival, providing shelter, fibers for weaving and wood for implements.

The fruit of California palms is far from the large dates we know. It is small, with a hard, black shell that protects the inside seed and flesh from insects. This fruit production is related to why the Cahuilla periodically burned their wild palms. Ethnobotanists discovered that burning greatly increased the amount of fruit a palm produced. The burning may have also been for pest control. The giant palm boring beetle produces a large grub that tunnels into the palm's trunk and if it reaches the head or heart of the palm, it can kill the tree. Burning may have created temperatures high enough to kill the grubs.

Wild California fan palms wear a "skirt" of dead fronds many feet thick which can accumulate to cover half the length of its trunk. Although it provides valuable habitat for wildlife, it can be dangerous to live beneath them. Desert winds cause large, heavy, and wickedly thorned fronds to break off and fall. Burning away the skirt after harvesting fronds for thatch and other uses ensured a safer life within the groves.

California fan palms are exquisite trees for the landscape and more cold hardy than their Mexican cousins. In 1990, a hard statewide freeze gripped California for a week wreaking havoc with trees and shrubs that were marginally hardy. The Mexican fan palms suffered far more damage than their California cousins.

This may be due to the thicker trunks, which are composed of bundles of water carrying tubes resembling a handful of pencils bound by a rubber band. When exposed to serious cold the outer tubes freeze and die. These become like a layer of insulation all around the living interior tubes, protecting them against future freezes. This is why a young palm will be less cold hardy than an older specimen of the exact same species. It also explains why the fatter trunk of the California palm has more insulation than the thin Mexican species.

California fan palms are an outstanding plant for western landscapes. But the key to it all is buying the right Washingtonia, so you don't find out 10 years down the road its a skinny robusta and not a fluffy skirted filifera.

Online: www.plantapalm.com

(Maureen Gilmer is a horticulturist and host of "Weekend Gardener" on DIY-Do It Yourself Network. E-mail her at mo@moplants.com. For more information, visit www.moplants.com or www.DIYnet.com. Distributed by Scripps Howard News Service.)