unknown blue green

I keep wondering what this plant is that grows in my neighbor's garden spot- it has light blue-green leaves with an airy appearance-

grew over the edge this year where my gladiolas are-

but it's really quite tall, over my head! six feet or more.

I seem to remember this same plant growing last year but in a slightly different spot. I do think it's kind of pretty. Will have to ask them next time someone is around.