Yes, Virginia...pampas grass (Cortaderia selloana) does indeed grow in Denver...although not in great numbers. Observant visitors will have noticed them dotted here and there at the York Street gardens, and I have seen another half dozen driving around Denver. The one above is right next to University Avenue, and constitutes a minor traffic hazard as grass-afficionados notice it and swerve! I suspect the owners purchased it via mail order, since these are rarely sold locally ("pampas grass is not hardy" according to most pretty well-informed nursery folk. And I agree, most are not. Only the dwarf, high elevation forms are apt to be hardy here, and these are hard to find).
Most Coloradoans probably don't know that pampas grass is a pestiferous weed in California--but then one man's weed is another man's treasure. I doubt that this will ever pose much of a threat in our climate. I share this picture to show that much of the creative work of plant experimentation is undertaken by home gardeners. We at the Gardens sometimes have to run to keep up!
Here you can see from closer up the silky, silvery color that true pampas grass has seemed to perfect. If you have driven parts of Texas you are sure to have admired pampas grass--a popular landscape plant in that state. I used to drive down at Thanksgiving each year, and the clumps of pampas here and there along the way were like mile posts, or sentinels that cheered the trip. Their fluffy seedheads are amazing when they puff up. Alas! A well established clump is so massive that cutting it back each year is a chore. This is one of the hazards of growing large grasses anywhere.
Confusingly called "hardy pampas grass" (a paradox if you think about it...), this is the most commonly planted giant grass around Denver. I am sure half the people who grow it think it is pampas grass, and if you look up and compare, you will see there is a family resemblance. But while the TRUE pampas grass comes from South America as the name suggests, Ravenna Grass is from the Mediterranean. This still grows abundantly in the coastal marshes near Ravenna I've been told. This is by far the most vigorous and giant of commonly grown grasses, and a large clump will often produce vigorous seedlings nearby that should be dug while young. A large clump needs a front end loader to move or remove...be warned! Until recently it was classed as an Erianthus, but has been put in the same genus as sugar cane in the last decade or so (Saccharum). Sugar cane has helped make Brazil energy self reliant. Maybe this vigorous grass has biomass potential? The group that has been exploited most for that in America is another genus altogether, however...
There are hundreds of cultivars selected from the various species of Miscanthus--which is also often sold as hardy pampas grass. They are hardy enough but the name is taken, I'm sorry. A great deal of research is being done on these because of their famous C4 metabolism which allows them to accrue enormous biomass in short periods of time. Miscanthus have nevertheless been practically banned in much of the eastern U.S. due to their propensity to produce colossal seed crops. I have yet to see a seedling appear in Denver outside, so I think we can grow these without guilt--except that these are the most water demanding of these larger grasses. Don't try them in your Xeriscape!
My current favorite giant grass is native not far from us here in the Rio Grande Valley. Plant Select has chosen to feature this plant in 2006 and I can vouch for its toughness. The plant you see in the picture is in my garden, on very sandy soil where it bakes for months on end and gets precious little water. Even so, it makes a fabulous fountain of golden seedheads that persist through the winter months.
Indeed, all of these pictures were taken this morning, January 24. The greatest reason to grow these pampas grasses (and their pretenders too!) is that they provide drama, beauty, movement and interest in the depths of winter for months on end. If you grow them, please resist cutting them back until February so we can enjoy their splendid display! But do cut them back hard so that the new growth will be fresh and green for the coming year!