Q: I have a plot of cannas in my backyard that is crowded, overgrown and just not pretty any more. I want to get rid of the cannas and replace them with gardenias but without a lot of digging.
A: Cannas aren’t terribly tenacious but I think you’re too late to do much damage with herbicides this fall. Go ahead and cut the brown leaves down and spray the cut stumps with glyphosate (KillZall, Roundup, etc). Till the plot in winter to expose the roots to freezing weather. Spot spray the new leaves in spring and plant your gardenias in their midst.