If you dig yours up in the fall anyway, you can get away with planting them a little closer. Cannas need room to multiply, and if they are too close the ground becomes too compact.

So if I plant them to close they might not multiply, but will they still bloom this season? Not the brightest question, but I don't want to waste them.

Spacing of canna rhizomes depends on several factors. The 18" recommendation is generally suggested for the spacing in a "bed" of cannas and not a single row or two. The length of the local growing season is certainly a consideration. The most obvious reason not to space closely is to prevent the mature rhizomes from becoming entangled and creating serious difficulty in separating each cultivar at harvest time. If all plants are of like kind, that is not a problem. In areas where the growing season extends for several months, lodging of the plants, bloom reduction, disease transmission, air flow reduction allowing the plant foliage to dry, etc. are often associated with dense populations of plants. These concerns should be considered.
In most growing areas it is much better if the cannas are spaced to allow for maximum growth. Depending on oneÂs planting area, 12" to 18" is a better choice in my opinion.
Kent

I do agree with you Kent. Air circulation is indeed a very valid consideration. I should have mentioned where I plant mine, they are in a row in an area where there is a constant wind blowing. I have no problem with mold growing there. I still like the clump look though, but based upon your recommendation, I will probably stretch the space to about a footapart. Thanks for your input.

Thank you for info!

Last spring I planted about a dozen cannas, 12" apart. They mulitiplied like crazy during the summer and fall. I will likely need to thin them next spring. I would recommend spacing them no less than 12", unless you don't mind thinning them every couple years.

How far away from a wall space do you need when planting next to a fence or wall?

Giuseppe I am wondering the same thing as I am currently working the solid and prepping a north facing wall of our home for some Cannas