It may be very common all over the world to bring flowers to people who are confined to hospitals. However, here in Japan, bouquets are okay, but you shouldn't visit them with potted flowers. Why?
Potted flowers can give us the image "taking root", which is called "Nezuku" in Japanese. Then the word "Nezuku" has the same meaning as"being sick in bed" in Japanese.
Hence bringing potted flowers might be considered like saying "Please be ill in bed." or "Please keep being hospitalized for a long time". Therefore if you bring them, people might regard you as foolish.