No Pampering Pampas Grass

Cortaderia is a genus of 20 species of ornamental grass, only one of which is grown commercially. This is peak flowering month in the garden for a couple of the lesser-known species of pampas grass. The first is Cortaderia araucana, which hails from Central/Southern Chile and Argentina. It’s much smaller than Cortaderia selloana and has performed beautifully for us in the garden.

Cortaderia egmontiana is also native to Chile and Argentina. In the two decades we’ve grown this, it has behaved beautifully, and is also slightly smaller than Cortaderia selloana and flowers over one month earlier.

Cortaderia selloana ranges from Bolivia south in to Brazil. It is the only species widely cultivated in the US. Two US states have put it on their invasive species list, but despite years of searching, we have yet to find a scientific paper documenting such tendencies. In California, Cortaderia selloana was grown for cut stems after the mid 1800s, and transported by open train across the state. As you can imagine, seed blew out of the train and it naturalized in adjacent open habitats. I’ve traveled these routes, and seen isolated clumps of pampas grass, but must have missed the areas where it chokes out native flora.

On its website, The California Department of Fish and Wildlife (CDFW) writes:  “Cortaderia selloana is a quickly growing grass that forms massive clumps along roadsides, steep cliffs, river banks, and open areas that have been disturbed by human activities or natural disturbances.” In other words, it is well-adapted to disturbed habitats, compared to say, California natives. This is fascinating since “natives” are constantly touted to be much better adapted. If seeding along disturbed areas is a reason to ban a species, how about an effort to ban Cannabis sativa and put it on the invasive species list. There are hundreds of miles of Iowa roadsides densely carpeted with cannabis, a leftover from the hemp crops of earlier this century, when over 400,000 acres of it were grown during WWII. It’s much easier to pick on plants that don’t have an army of advocates.

CDFW goes on to write, “Invasive plants such as pampas grass displace native plants and create habitats that are lower in biodiversity. Furthermore, pampas grass has leaf blades that are highly undesirable as food or shelter to birds and other wildlife, and can actually cause physical harm to those animals, including humans, because the leaves are extremely sharp.” Really? Cactus, agaves, dasylirion, nolina, etc. all have equally sharp leaves…are they not a problem? Where is the science which backs up these claims? We certainly can’t find any. It seems that most websites simply repeat the same text without any backup scientific data.

Cortaderia selloana is primarily diocious, meaning it produces male and female flowers on different plants. For sake of full disclosure, hermaproditic plants (with both sexes) have been observed in the wild. Since the most showy plants are female, that’s virtually all that’s commercially grown, unless someone grows a seed strain. Having grown Cortaderia selloana for sixty years, including some from seed, we have yet to see a single garden seedling. Perhaps there are areas in the country where it shouldn’t be grown, and if so, we hope you will share the URL of the scientific papers that document this. Hardiness zone is Zone 6b-10b.