Ever drive along the roadways of California and notice a huge, fountainy grass with big, feathery, buff-colored plumes? To the untrained eye, pampas grass (Cortaderia selloana) looks like a statuesque, beautiful grass, but oh! Beware!
In her wonderful horticultural history, Southern California Gardens, Victoria Padilla tells how in the mid 1800s, Joseph Sexton “the father of horticulture in Santa Barbara” popularized pampas.
Vast acreage was devoted to pampas as demand grew, not just for garden plants but also for plumes to decorate hats and other items. “Pampas grass became so popular.” Padilla writes, “that it was almost a national emblem, and was used not only for indoor decorations, but for parades and even on holiday greeting cards”
If only Sexton had known what would happen not a full century later. Pampas was so well adapted to growing in California’s Mediterranean climate, this South American native has become one of our worst invasive plants. It invades natural habitats, crowding out the plants that native animals depend on for food, shelter, and cover. It clogs waterways causing the buildup of sediments and again destroying native habitats. Its dry leaves and plumes allows fire to jump from plant to plant, even across wetlands.
Pampas’ destructive nature has not gone unnoticed. There are efforts at every level in the state to stop the sale of pampas in nurseries. At the same time, millions of dollars are spent annually in eradication programs both for habitats and for garden situations.
In fact, home gardener Sandy Shapiro initiated a backyard pampas eradication program in his hometown of Encinitas, California. Project RIP, or “Remove Invasive Pampas Grass” was intended as a model program to show residents how to get pampas off their properties.
Still, wholesale and retail growers continue to offer dwarf and variegated hybrid pampas such as such as ‘Gold Band,’ ‘Silver Comet,’ and others. Because identical looking seedlings don’t pop up in the nurseries, they assume these plants are sterile and “safe” for garden use. But are they right?
Not according to Marie Jasieniuk, Assistant Professor in the Department of Plant Sciences at UC Davis. Jasieniuk identified genes found in both wild (invasive) pampas populations and cultivated landscape pampas varieties sold by nurseries and garden centers in California, in other states across America, in Europe and New Zealand. She compared the genetics of cultivated varieties to 29 wild populations of pampas from Crescent City in the north to La Jolla in Southern California.
Jasieniuk’s research determined that wild populations of pampas have genes in common with the so-called sterile, cultivated varieties.
In other words, while they don’t breed true-type offspring, cultivated pampas definitely breed with the wild growing pampas and contribute to the overall problem of invasive pampas.
According to Jasieniuk, ” landscape plantings are probable sources of invasive populations… Our results strongly suggest that …. landscape planting has contributed to the range expansion of invasive C. selloana in California.”
Further, results suggest that even as we spend millions of dollars eradicating wild growing populations of pampas, landscape plantings continue to “replenish” the wild populations. Therefore, Jasieniuk writes, “management efforts that target secondary releases by eradicating landscape plantings may be highly effective in controlling existing invasive populations as well as preventing further invasive spread.”
In other words, to eliminate invasive pampas from both native habitats and cultivated areas, we need to stop planting all varieties of the pampas, Cortaderia selloana in our gardens.
Beautiful but dangerous. Sounds like the beginning of a good novel. If only it were fantasy rather than reality….