I haven't seen a real bike used for that purpose. I've seen a few planters made to look like old cruisers, but smaller than the real thing.

Old school buses, toilets and all manner of other things I see regularly. One guy arranges a wide array of junk in an arrangement that I assume means something to him. The material changes regularly and once included a bike with a bottle of pink lemonade in the bottle cage. Last week it included three old riding mowers propped up on their back wheels. Sometimes it's all accompanied by a large crudely painted sign that's religious in nature. It's art to him and over the years I've come to appreciate it.