Cannas grow pretty quickly (and they get very tall if you fertilize) but if you are like me and can't stand to wait for bloom you better go w/the 12" one, make sure you bring them in and store them when it gets below freezing or they will die. (the rhisomes)

Since you are located in a Z4. Buy the cannas already growing you'll put yourself at least a month ahead of schedule since your growing season is so short.

Fertilize'em with a lower nitogen, I use 8-20-20 slow release pellets. The will multiply fast, make sure you container i slarge enough to handle the growth. I would not use anything smaller than a 12" pot. I used an 8" clay pot last year, I always meant to re-pot but never did, anyhow the cannas busted the pot into pieces later in the fall. Have fun.

Joe

I use horse manure (I've got plenty of that!) I don't have to worry about how much fertilizer i'm adding that way (it don't burn) and the results are still excellent!

Thanks to all for the information -- I'll think I'll go with the "already growing" plants. I am planting them in 24" diameter containers - so I hope they do well. I've always thought they were such a beautiful plant. If it works, I'll post pictures later.
Joe - what type of fertilizer would that be? I normally use Miracle Grow Plant food, but it doesn't have those same numbers.
Sharon

A local comapny here makes the stuff I use. Miracle Gro works fine. It just has a little higher Nitrogen level than I like. I think they have a slow release pellet that is 10-10-10. The higher nitrogen doesnt really burn the canna, it elongates them. I like my cannas with plush foliage. I used composted manure this spring in some containers and it is doing wonders to those plants. I am already having blooms!

Joe

Also, just a word of advice from one canna newbie to another... :) please read the excellent information on identifying the canna virsuses so you don't take home an infected one.

I have cannas that I got from my neighbor a year ago, and they grow very fast, a canna that my neighbor has is suppose to get 8' tall and it got nearly 12' tall, she put it in a warmer spot in her yard with lots of afternoon sun, and she did not give it any plant food. I got plants that were growing that I got from lowes, and I planted some of the bulbs in the ground and they bloomed at the same time. here in zone 6b my neighbor leaves one of hers in the ground in a protected spot all year.