Question about Grasses

Question from Jon:
Jon in La Mesa here again. I have a question for you regarding native grasses. I am attaching a couple of photos of some grasses that are on the top slope of our yard. They are all over the area (Mt. Helix area of La Mesa). We just finished the first phase or our low water landscape project and we decided to leave these grasses intact because we like the way they look. The question I have is will they eventually take over the yard, or will they stay relatively confined to an area? We have a good layer of mulch down everywhere around all the bare areas, so I doubt they would seed themselves thru the mulch. But I don’t really know anything about them. I have spent a lot of money on planting and I don’t want some invasive grass to take over and choke out all our efforts.

Any info or advice you could provide would be appreciated.

Again, looking forward to your April talk at Master Gardener seminar.

Thanks a bunch!!

Answer from Pat:
I agree this grass looks very nice, except I would cut back the dead stuff and shear off the flowers annually in fall. I am not sure what it is though it appears to be some kind of carex which may be native. If so, I can guarantee it will seed itself though it might not be a huge problem. (I have Carex pansa, a native evergreen grass, in my garden, it does spread from seeds but is not too much of a nuisance, since i am able to transplant the clumps that volunteer into an area where they are useful.

If this is ordinary fountain grass (Pennisetum setaceum), an African plant, it will be an awful problem and this has been a badly invasive plant on road edges where it was planted by Caltrans. Red fountain grass does not make seeds but the green variety is hugely invasive as is Mexican fountain grass. One of those plants has even sprung up in my garden though it’s not growing in any other garden within a quarter of a mile.