Pampas Grass

What’s still blooming somewhere: Tea roses, red hot poker, winecup, scarlet flax, drab chamisa, chocolate flower, chrysanthemum, Mexican hat, áñil del muerto, tahokia daisy, blanket flower, hairy golden and Mönch asters; yellow leaves and fallen apples litter the ground, grapes shriveling into raisins.

Inside: African aptenia and asparagus fern.

What’s turned/turning red: Lapins cherry, Bradford pear, pasture rose, spirea, raspberry, sand cherry, Virginia creeper, leadwort.

What’s turned/turning yellow: Cottonwood, globe and weeping willows, Siberian elm, tamarix, beauty bush, sour cherries, peach, rugosa rose, Apache plume, lilacs, hosta, Rumanian sage, catmint, yellow alyssum, Silver King artemisia, purple coneflower.

Animal sightings: Rabbit, large black harvester and small dark ants.

Weather: Rain Tuesday and Wednesday, followed by mornings so cold frost lay on lawn grasses and water froze in the village arroyo; 10:18 hours of daylight today.

Weekly update: There are times when I drive by someone’s yard and see something so beautiful, I wonder "how’d they do that."

Near the village someone has two magnificent clumps of pampas grass at the end of her driveway that have thrown up white plumes that wave 6' high against a backdrop of yellowed trees.

It may sound quite ordinary, except Cortaderia selloana is a zone 8 plant that can survive in zone 7 Albuquerque in favorable situations. There are some shorter cultivars like Pumila which tolerate zone 6 Santa Fe. But, Española is zone 5. The average low temperature for zone 8 is twenty degrees and, even in our mildest winters, there are mornings in the high teens.

Many western gardeners have learned the USDA system of zones is more reliable in the east than on the plains and in the Rockies. The idea of using a single variable, mean low temperature, to predict that ability of plants to survive was introduced in 1927 by Alfred Rehder, who was interested in describing the vegetation belts he saw across the country and the Appalachians.

According to Peter Del Tredici, Donald Wyman redefined Rehder’s concept to use the average minimum temperature in 1938 when he was at the Arnold Arboretum. He and other specialists continued to issue competing modifications until the USDA published the standard developed by Henry Skinner in 1960 at the National Arboretum. The agriculture department has since issued several revisions, and other groups, like Sunset magazine, continue to publish alternative guides for this part of the country.

But no matter how sensitive the tool, nothing will explain how those thriving South American plants have survived at least one winter.

The owner has done everything she could to create a favorable environment. The land around her house is surrounded by high, stone walls, that also line both sides of the sealed drive. In the winter the dark walls and paving absorb daylight, then radiate heat as they cool in the night. The surrounding microclimate is warmer than the prairie.

The owner has also been helped by her location. She lives about three-quarters of a mile from the river and about five hundred feet from a wide arroyo. A concrete-lined irrigation ditch passes near the outer wall carrying water in summer. Trees across the road help deflect the drying
winds of February.

Her natural and manmade location helps, but still can’t explain what makes her rhizomes so successful. My friend from Uruguay tells me what he calls horses’ tails grows on the sandy beaches of the eastern shore where the coldest it gets in winter is a few degrees below freezing. Tour groups advise it can be seen in its native habitat in the Costanera Sur nature reserve in Buenos Aires on the Rio de la Plata.

It also grows to the southwest at the Ernesto Tornquist Provincial Park with the 3,700' Cerro de la Ventana about 75 miles inland from the Atlantic. There, Natalia Cozzani and Sergio Zalba have found birds nesting in the tussocks of dried grass that accumulate beneath the fountains of sharp-edged foliage.

Pampas grass prefers moist winters and dry summers, but is not restricted to the coast. The perennial is also found in Brazil, Paraguay and Chile. Texas A&M has published a photograph of white heads growing like dense scrub in western Mendoza province in what looks like a tree-lined mountain meadow backed by snow-streaked peaks.

The wild species, which can reach 20', is probably not the one available in trade: nursery catalogs advertize 10' heights. Many are probably sterile cultivars that don’t shed the pollen, flowers and seeds my friend says fill the Uruguayan air. My neighbor probably has a hardier cultivar, but it’s still unique in this area for its height, width and vitality, a wonder to behold.

Notes:
Cozzani, Natalia and Sergio M. Zalba. "Estructura de la Vegetación y Selección de Hábitats Reproductivos en Aves del Pastizal Pampeano," Ecologáía Austral 19:35-44:2009.

Del Tredici, Peter. "The New USDA Plant Hardiness Zone Map," Arnoldia 50:16-20:1990.
Rehder, Alfred. Manual of Cultivated Trees and Shrubs, 1927.

Texas A&M University Herbarium. Vascular Plant Image Library photograph of Cortaderia selloana taken by Hugh Wilson.

Photograph: Pampas grass in the wind, 17 October 2009.