Sabal uresana

Sabal uresana, the Sonoran Palmetto, is the only Sabal species endemic to the Northwest Mexican state of Sonora where it is now relatively rare, although larger stands exist is some areas, including Opodepe, Mazocahui, Onavas and Soyopa. Its range also extends a little beyond Sonora into south-western Chihuahua and northernmost Sinaloa. This very attractive palm which has a distinctive silvery-blue foliage, particularly when young, grows in a variety of complex interconnected topographies and habitats which are in turn subject to a distinct local pattern of seasonal meterological change.

Following the line of the Sierra Madre Occidental northwest from Northern Sinaloa and Southeastern Sonora through to West Central Sonora, it is found inland in oak woodland to elevations of 1200 m then down through the dry Tropical Deciduous Forest (TDF) and its foothills particularly where it borders into thornscrub and following the river drainages into Sonoran desertscrub. Along the eastern coastline of the Sea of Cortez, it can be found among the coastal dunes and canyon bottoms around San Carlos and Guaymas, into Las Barajitas Canyon and following the river drainages north along the edge of the TDF into the desert. East of Hermisillo around Ures - the capital city of Sonora from which the species gets its name - the countryside is desertscrub and the wetter thornscrub. These inland populations are more distinctly silvery-blue than the more glaucous-green coastal palms and the more northern populations are larger in overall size than the more southern populations. In this north-central Sonoran region, it grows in sandy plains, along water courses, arroyos, canyon bottoms, floodplains and other riparian niches and into the low hills as far north as Opodepe where it can be found around springs in the mountains. It is thus the most xeric of the Sabal species but always following the water and always growing in deep sandy soils and unlike the four Brahea species that also grow in Sonora, it does not grow on rocky slopes. These gritty soils, comprising alkaline calcareous sandstones and fertile potassium-rich silts, accomodate the strong deep root system that Sabal uresana likes to put down. Raising Sabal uresana in containers therefore, is a challenge and like so many palms, once it gets its roots into the ground its growth-rate is much quicker. The Tropical Deciduous Forest is not usually thought of as having frost but even as far south as Alamos there are winter nights when a very rare freeze occurs and snow on the high ground in the Sierras is not infrequent during the winter. It is remarkable nontheless that Sabal uresana is as cold hardy as it is and that it is capable of withstanding freezes down as low as it does. Usually quoted as being hardy to about -5C we have found it tolerates temperatures lower than this.

The Sonoran Desert is the wettest of the four great North American deserts and the state of Sonora has a climate pattern that gives it two distinct wet seasons: the heavier rainfall of the summer monsoon and the lighter more prolonged winter rains, separated by spring and autumn dry seasons, with sometimes - particularly in the south - a moist autumn generated from tropical storms bridging the two wet seasons. During summer - the wettest season - the Tropical Deciduous Forest and the thornscrub are transformed into rich verdant growth. Temperatures in summer are usually above 30 C and this combination of high heat and high precipitation are the key to understanding much of the cultivational requirements of Sabal uresana together with the deep potassium and calcium-rich gritty soils in which it grows.

Trying to reproduce the bi-seasonality of the rains would not be a problem in Britain, a country blessed with rainfall, but given the lower temperatures that are encountered here in winter it is better to try to keep the palms - and particularly their roots - as dry and warm as possible. A thick winter mulch is sensible as is fleecing to avoid frost-burn. What may be more difficult to reproduce is the high summer heat during the growing season. When planting it out, it needs to go in the sunniest, warmest and most-sheltered spot that you have. Creating a heat-absorbing cover of black Mypex around the palm is a useful method for generating local heat.

This is probably the most attractive of all the Sabal palms. Although slow it eventually grows very tall and with its deeply-split, silvery-blue foliage, pendant leaflet tips that end in hanging threads and long smooth petioles that extend well into the costapalmate leaf blades, it makes for an extremely handsome specimen that deserves to be more widely grown.