Nassella tenuissima - A new urban weed

I have always had some concern about the (somewhat) recent surge in ornamental grasses in the horticulture industry. I have been following several species over the past few years that have been of particular concern for their "weedy" potential.

Nassella tenuissima, Mexican Feather Grass, is one of the species that has grabbed my attention. It seems to be the new trend in covering large expanses with grasses, in park and streetscape settings (and can even be found on some roof gardens). I will admit that there is something spectacular about its fine textured plumes dancing in the breeze, and it is quite drought tolerant in our California climate. However, the nursery industry seems to be more concerned with making a buck than considering the invasive potential of this species. And designers seem to be either ignorant or naive about the invasiveness of this species.

Rick Darke mentions in his 1999 publication, The Encyclopedia of Ornamental Grasses that it "self sows readily and can be a minor nuisance...May be capable of naturalizing in areas such as California." Well, his "may naturalize" should now be revised to "will naturalize." Other nursery professional and ornamental grass experts, such as John Greenlee don't seem to be as concerned. Greenlee recently participated in a design project at the Port of Los Angeles and recommended the use of acres (yes, acres) of N. tennuissima. At another project, here in Oakland - Union Point Park - N. tennuissima has been used liberally to paint the landscape. While the effect in this seaside setting is pretty alluring, the City of Oakland is now faced with a huge maintenance nightmare.

Grass seedlings are readily sprouting up all over the place. Strangely, the most consistent location for these seeds seems to be in the joints of the paving, although seedlings can also be found in tree wells and many of the large planting areas throughout the park (note that the park opened in September 2005). Note the many seedlings sprouting up in and around this tree well.

My father, an avid plantsman, got into ornamental grasses several years ago. When he mentioned purchasing some Mexican Feather Grass I cautioned him about it's potential to naturalize in the garden. At the time, he didn't take me seriously and said that he'd just pull up the seedlings if they came up. Now he is also faced with a maintenance issue and must work to pull these up from the cracks in the driveway and elsewhere where it is unwanted.

Luckily, my father is quite green and sustainable, so he won't be spraying RoundUp all over the place to keep these prolific colonizers at bay. But I do worry about places like the Wilmington Waterfront and Union Point Park. It won't be long before this grass takes over and spreads into the surrounding neighborhoods, sprouting up in the sidewalk, in peoples gardens, even on roofs.

I'll be watching this grass as it becomes a primary weed of concern in California, as Scotch Broom, Pampas Grass, and many others already have. It won't be long before it is listed on the invasive species list as it is currently in Austrailia where it is a State Prohibited Weed. As urban weeds go, this is probably one of the most aesthetically pleasing out there, but that is no excuse for us designers to knowingly spread this noxious weed around our cities.

If you have any experience with Nassella tenuissima, please share your thoughts. I am also trying to collect images of this and other grasses spreading and setting seed; if you have any you'd be willing to share, please do so.

Comments

[Sally]

Welcome to blogging! Thanks for the information. Could you post a bigger picture of this grass? I want to keep an eye out for it.

I saw Nassella tenuissima today in the Angeles National Forest chaparral burned area about 10 mi NE. of Santa Clarita above Boquet Canyon. The grass was growing in rock cracks on a near vertical rock outcrop. About 25 plants in a 50'area. This surrounded by 1000's of acres of chaparral with rock outcrops.

[James]

I was drawn to this plant several years ago when it hit the nursery trade and bought a couple for my San Diego garden. It's an amazingly graceful plant and many people are drawn to it immediately. My two original plants have long been pulled out but their progeny are now all over my yard. In wet months I'm certain I pull out dozens of the seedlings every week. A new church landscape project a couple miles away has used masses of these. They're gorgeous, but I feel sorry for all their neighbors that are now about to be bombarded with the seedlings. I'd definitely argue against using this plant considering its invasive tendencies.

Native California N. cernua would probably be a more responsible substitution that would give a similar effect.

[Margaret Lane]

This grass is a native grass. How can it be considered invasive? Check the usda.gov website.

http://plants.usda.gov/java/profile?symbol=NATE3&mapType=nativity&photoID=stte4_001_avd.tif

[Paul]

Check out this site for an explanation about its invasiveness.

http://www.issg.org/database/species/ecology.asp?fr=1&si=463&sts

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Hello let me tell you my father is quite green and sustainable, so he won't be spraying RoundUp all over the place to keep these prolific colonizers at bay. But I do worry about places like the Wilmington Waterfront and Union Point Park.
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