the sunflowers in one of my school gardens grow to 4" thick. Yes, that's how good the sun is.
I am being very selective about where I let them grow this year because last year they turned the water off on us too early (maintenance staff thinks gardening ends on 10/31, LOL) and I didn't have enough water to get the stems out. We literally had to use a chain saw to saw them down and now the root and chopped off stem are in the beds and we'd have to dig them out. Plants have grown around them, unfortunately, so can't do it now. Will have to wait until those plants, like tomatoes, etc., are spent.
We have many passersby at the gardens and people love to stop the gardeners and talk. One of the most frequent topics of conversation is how magnificent the sunflowers are.
Bamboo does some interesting placement, too. I have a bamboo forest to the east of me, which I let grow as a privacy means. This year the bamboo grew in such a way as to provide bannisters for the stairs! I love it that I can have a pole to hang on to if I need it.