It's generally recommended that canna tubers be planted 12-18 inches apart, though in cooler climates where they'll be dug up each year and are less susceptible to disease, a bit closer planting is probably going to be OK. Spacing also depends on the variety (dwarf hybrids can tolerate tighter spacing than the giants).

Here's a recent GW discussion on the subject (note the regional differences).

O.K. I get the spacing. Thanks for that! But what about the look. Better to have 1 group of 10 plants together or two groups of 5 or some other variation? I can buy more if I have to. Not looking for the jungle look, want some room to see individual groupings.

Thanks,
Lee

Massing makes for a more impressive show. I'd look at 10 tubers as a minimum number. Of course, if you're more interested in having a wide variety, you can group smaller numbers of several different kinds which have compatible growth/flowering. It's a matter of taste, but you might want to avoid having 5 cannas over here, then some other ornamental, then another small clump of cannas etc.

Eric thanks for the info. I went out and bought another 10 last week. Also a bunch of the sun coleus, gunnera, japanese blood grass, and about another $100 worth of stuff. Only went for the canna's but you know what happens when you get in the nursery!!

Lee

Ooh, Japanese blood grass, that sounds cool! I notice you're in zone 5 too. Is that hardy to our zone?

It is hardy to -10, so I will need to mulch it somewhat. I grow alot of stuff that is outside zone 5 as perennials, some just need a little help through the really bad days. Even some stuff that says zone 5 is marginal without help.

Lee