I don't know how you kill weeds with a pond liner, will the liner stay
at the bottom and grow things around?

Roundup would work fine but just temporary, weeds will allway's come
up later and weeding is still needed after. I have borage, sunflower & poppies.. weeding is the main annoyance. Perhaps something dense like clover, I'm sure, you can grow more things in your climate...how about lavender?. I tend to grow more trees & shrubs for bees...good
for the long run.

I'll put pond liner down, secure it and wait. It will kill everything under it. I NEVER use roundup - it is not safe as the company claims. It is made by Monsanto which is a horrible company!
I'll plant clover (it's a smoother crop - no weeding) but it would get a bit monotonous. So I could put other things in like borage, poppies, etc. Thanks! Look up Monsanto on the web, not the monsanto web site.

Good for you!...how long do you have to keep the liner down?

About a month of summer sun should do it.

SOUNDS LIKE A GOOD PLAN. I USED PLASTIC AS WELL, BUT WHEN I DECIDED TO PLANT, I JUST CUT OUT HOLES IN THE PLASTIC AND PLANTED IN THE HOLES, KEEPING THE WEEDS FROM COMING BACK. EVENTUALLY I HAD NICE PLANTS SPREADING OUT TO COVER THE PLASTIC AND IF I FOUND A NEW PLANT I LIKED, I JUST CUT ANOTHER HOLE AND POPPED IT IN.