If you come to Portland one of the best things to see is the International Rose Test Garden at Washington Park.
(By the way, this is not my photo. I snagged it from the gardens of merit web site.)
If you are here in June you can take in the Portland Rose Festival. Lots of activities and parades. The Grand Floral Parade is like the Pasadena Rose Parade. All the floats are made from flowers. We have never gone. I'm just not much into parades and this is one where people camp on the street overnight for a good viewing spot. I can't deal with that.
The Rose Festival is laden with tradition and pomp and is a big deal for many Portlanders. We didn't grow up with it, so it all seems a bit overblown and past its prime to me. Especially the "Queen of Rosaria" competition. Each High School chooses a Rose Princess, then there is a big pageant to choose the queen. The year we moved to Portland Emily was a Jr. in High School. She was into wearing black and big Doc Martens and hated the High School she landed at. One day she came home and said, in a voice dripping with disdain, "Today we had a big assembly and chose our school's Rose Princess." Then she stuck her finger in her mouth in a gagging gesture and went "Gack, gack!" I was quite amused and always think of that when I start seeing the pictures of the Rose Princesses show up in the newspaper each spring.