I'm new to Canna's this year and I have a ton of them potted on my deck and a ton in the yard planted in the ground. Several on the deck have started to get crunchy around the edges of the leaves. Is this some kind of disease, are they getting too hot (it's been in the high 90's and/or over 100 here for weeks) or is it something else? And how do I fix whatever it is? I absolutely love my Canna's and want to do whatever is needed to keep them gorgeous.
I agree with reflective heat, as well as the extra warm weather. Cannas can deal with extreme heat, if you keep their roots at a healthy moisture "norm". Unfortunately, once the weather gets very hot, they soil dries out, we panic, then soak the plant, then it dries out, we panice and then soak them, etc. If you repot them, look to see if they are crowded under the soil...and also repot them in the Miracle Grow soil that has the little granules in it for moisture retention. That seems to balance them throughout the drought/heat then to rain/soak...back to drought/heat to rain/soak season.
We're just about to move into the cut-worm/leaf roller season...so watch out for that on the leaves too!
I grow them in a hot location and do see some bottom leaves occasionally turn brown. But as long as most leaves stay green, the overall health of the plant does not seem to suffer. Many bloom like crazy during these high temp months even with the occasional brown leave. I do have to water them more once temps hit 100.