I found these wonderful images of vintage seed catalogues on the Smithsonian Library’s online collection.
The seed trade catalogs document the history of the seed and agricultural implement business in the United States, as well as provide a history of botany and plant research such as the introduction of plant varieties into the United States. Additionally, the seed trade catalogs are a window into the history of graphic arts in advertising, and a social history, through the text and illustrations, showing changing fashions in flowers and vegetables.
It is a wonderful resource, as you can search by plant, image content or company. Here are some of my favourites.