What perennial flower can you grow in a medium sized flower pot?

Perennials are such because they often have major root systems or a storage vessel underground which allows them to come back year after year. Confining the root system in a "medium" pot risks the plant as well as the pot. Personally I'd grow annuals in the pitcher that would allow me to empty it out over winter, clean it up and plan the next year's display. Probably the opening isn't that big.....if it was I'd find plants in pots that would fit down into the pitcher, saving the transplanting, just pull the pot. That way you could change up for seasonal display. Since most perennials only flower a few weeks a year, they should not be considered major ornamentals. It is the grouping and succession of bloom that constitutes a nice perennial display. Annuals have no need to spend time forming tubers/bulbs whatever underground so can put their "heart and soul" into season long flowering.

Not knowing where you are (or if it will be a houseplant), it's hard to say. A fern or spider plant would do nicely in that, especially considering the growth pattern (it would look like a head of wild hair). If you really want flowers, petunias, cyclamen, and violets would work...plenty others, but those are widely adapted ones.

It could depends - there are plenty of perennials with shallow roots - mini hostas can be one or you can try some plant that only grow a few inches and top the pot off with gravel/pebbles for a nice little rock garden look - the mini dianthus, bellflower, harebells are nice for that kind of container.

Perennials don't do well in containers because their root systems are too large. You could try a houseplant like an asparagus fern: http://lawnpatiobarn.files.wordpress.com/2010/04/fern_asparagus_setaceus.jpg Or use it for cut flowers. Zinnias and cosmos look so prety in pitchers. zinnias: http://www.jeanann.us/images/ziniasin-silver-pitcher.jpg cosmos: http://image.shutterstock.com/display_pic_with_logo/113263/113263,1253050597,1/stock-photo-freshly-cut-cosmos-in-antique-pitcher-near-window-edge-of-lace-curtain-included-in-composition-37129027.jpg

That's going to need space to spread and will suffer if it is not given the room to grow. this site has a lot of information on gardening like soil,pots,types of plants ect.

Just put a pot inside the pitcher - any plant wants drainage, pitcher doesn't have drain holes, too much water will rot roots, kill plant. It would be helpful to know how much sun/shade the plant will be in.

Violets would do okay.

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The only thing I can think of that would tolerate it well is Hens and Chicks.