I know that the bluebonnets won't last very long--I'm concerned about
them being able to come back next year.

I thought that portulaca was a perennial. In any case, I don't know
about annuals choking out grass, but there are some ground covers that
will--veronica is one. That was my other choice. But I thought that
would be even more difficult for bluebonnets to make their way through
next year. (What will choke one thing will probably choke another...)

I was hoping someone else had some Actual Experience with these two
plants.

Karen