Do nematodes infest cannas? I have nematodes and have to grow nematode-resistant tomatoes because of it. I planted some cannas in the garden and they did all right for a couple years but now do not do much. I might have gotten one flower last year out of a dozen or more stalks. Cannas in pots do somewhat better for me. Do you think I have a nematode problem?
I believe they can be susceptible to root-knot nematodes, but there are plenty of other things that can cause problems for them too. Do you have some pictures? Or descriptions of any symptoms besides just not blooming how you'd hoped? If they look healthy and just aren't blooming as much, I'd look at things like increased shade in the area or them being too crowded, either of those could cause decreased blooming.