Starting bed around established plants in grass

Hi, I feel like this might be a silly question, but I have some plants growing in my yard, they're in the lawn, growing out of a "base of grass." I don't want them to get buried by the grass, I can't weedwack the area because I don't want to hit the plants I want to keep, so I've literally gone out there a few times with scissors to cut down the grass that's growing up around & in between the plants.

My question is, how do I go about making this little space (2' x 3') a "garden bed" and or, how do I stop the grass from growing in between the plants? Can I simply put down mulch around the plants I want to keep to kill the grass? It gets a little more complicated because this plant spreads by rhizome (no, it's no bamboo, lol) & I want it to continue to spread. So if I put something like mulch down, will it be able to still sprout up through the mulch? I think that eliminates any type of fabric. Anyway, I thank you very much for your replies!!

My suggestion would be to put some cardboard around the plants you want to keep.  Maybe a base of 6 to 12 inches.  Then put a 6 inch deep mulch over the cardboard.

What kind of grass so you have and what are the plants you want to keep may help others offer other suggestions.

I would also mulch heavily. Mulch often makes the plants "looser" in the ground so they're easier to pull out.