Plant of the Week: Yucca rostrate; 'Sapphire Skies'; Big Bend Yucca
My first true gardening passion was for the cacti and succulent collection at the Oklahoma State University greenhouse where I worked as an undergraduate. Something about their bizarre forms and toughness appealed to me and always has. A few weeks ago, I was walking my dog at Wilson Park here in Fayetteville and spotted a stand of trunk forming yuccas that surprised me. It was a fine stand of Big Bend Yuccas (Yucca rostrata).
There are about 50 species of yuccas described, all of which are native to the New World. In North America, about 25 species are described with most occurring in the desert southwest. Once considered a member of the lily family, they are now classified as belonging to the agave subfamily of the asparagus family. Big Bend yucca is perhaps the most handsome of the trunk forming yuccas and hails from Brewster County Texas near Big Bend National Park and in several scattered sites across the Rio Grande River in the Chihuahua Desert of northern Mexico.
Big Bend yucca grows a stout (5-8 inch diameter), shaggy trunk that usually is unbranched until plants achieve some age, where several branches may arise from the crown. Usually plants are seen in landscape situations growing as five to six-foot-tall plants with a dense topknot of blue-green leaves but they can eventually reach ten feet in height.
The half-inch-wide leaves are to 2 feet long with a yellow margin. The leaf tip is spine bearing, but the leaf and spine are flexible enough to render the plant safe to have around children who don’t always watch where they are walking. New leaves form at the upper end of the stem while three year old leaves below wither and sheath the trunk.
When plants reach maturity, sometime after a decade or more of growth, they will send up a tall, symmetrical spike bearing hundreds of golf ball sized white flowers in late spring or early summer. If the yucca moth is present, a number of green, two to three-inch-long beaked pods will form. Beaked yucca is another common name for this plant. In fact, the Latin epitaph means beaked.
Forty years ago enterprising individuals developed a market for trunk forming yuccas collected from private land in West Texas. Half a dozen of these so called “arborescent” yuccas grew there, so for several years pickups and flatbed trailers began showing up from Georgia to California offering these wild-collected plants. I spent one summer in the library studying up on yuccas, so I would know what they were.
Most of the species died within a year or two of planting, but Yucca thompsoniana, a close relative of Y. rostrate and long considered the same thing, hung on more tenaciously and survived for a decade or longer. Digging plants from the wild and transplanting them into a foreign environment seldom works, so I was not especially surprised to see them disappear from northwest Arkansas landscapes.
But I was surprised a few weeks ago to notice the planting of five-foot-tall yuccas growing in the city park. After talking to the city’s horticulturist I learned the plants were a cultivar named “Sapphire Skies.” It was released by Portland, Oregon nurseryman Sean Hogan who grew it from seed collected at about 2000 feet elevation in Northern Mexico in the early 1990s. He operates a mail order nursery called Cistus Nursery specializing in plants with a Mediterranean feel to them. Because Big Bend yucca is slow to propagate naturally, he put it in tissue culture where it is still being propagated for wholesale nurseries.
Big Bend yucca’s success in cultivation is surprising on several levels. First, it is easy to assume it would lack winter hardiness coming from where it grows naturally. Not so. It is hardy down to -10⁰F. Secondly, its native habitat is high, droughty mountain ridges in areas that receive less than 15 inches of rainfall a year. Provided there is good drainage, it seems to tolerate winter-wet conditions just fine.
I first encountered “Sapphire Skies” in 2007 growing in a flowerbed at the Brooklyn Botanical Garden in New York. It was over 6 feet tall and apparently thriving in that wet, coastal city. The Fayetteville plantings were made in 2009 and 2011 from small pot-grown plants from Plants Delight Nursery in North Carolina. They are on a modest, south-facing slope in full sun. Planting nursery grown plants makes the job of establishment much easier for these xeric plants.
For more information about horticulture or to see other Plant of the Week columns, visit Extension’s Website, www.uaex.uada.edu, or contact your county extension agent. The Cooperative Extension Service is part of the U of A Division of Agriculture.