The historical cemetery there is a wealth of old garden roses.

Here is a link that might be useful: OGRs @ sacramento historic cemetery

Bus or taxi is not going to work, everything is way too spread out here--you really need to rent a car. A taxi trip to the closest nursery would start at about $30, and other cool ones would probably cost $100 to take a taxi. A bus ride would involve many changes and hours of waiting.

One place you could get to would be the park surrounding the State Capitol Building. It has many trees that were planted in the 1800's, with name plates as to variety and a walking tour available. There are amazing trees of all types from all around the world in the park, such as a huge American persimmon 4 stories tall with a trunk at least 6 feet in diameter. Many were gifts from different countries. There is also a beautiful and huge rose garden as part of it. Just don't pick the oranges--the cops will be on you immediately to tell you it's all government property!

If you do rent a car, I would say go check out Green Acres nursery (google it, 3 locations) the UC Davis arboretum, and Eisley's nursery in Auburn is pretty cool too. (Capital Nursery is also famous here, but something is going on with them lately (financial problems???) and their shelves are almost bare this spring.)

Carla in Sac

captial nursery
4700 Freeport Blvd
Sacramento, CA 95822
(916) 455-2601

This is a hidden gem because the website is not there, but when you go there is like a whole orchard of trees you can get lost in out back. I could spend hours there.