I have several patches of Canna Lilly which have sprung up by them selves. Unfortunately, they are the common 2 metre variety, with lots of leaves with a little red/orange flower. I have soaked the patch in double strength Roundup mixed with soap solution, BUT, it did nothing after 5 weeks, they actually look better than before. I want to replant this wet area with more exotic Canna's. Is there a way of chemically killing them or do I have to try and dig them out?
03 July 2013 06:06 AM
Canna lillies have a rhizomatous root system and once established, the plant can take a lot of effort to remove or kill off. Probably the quickest way of removing your clump of canna lillies would be firstly to dig out as much as you can,trying hard not to break off much of the root system, wait for the soft tender growth to re-shoot and then spray with a glyphosate solution. Even then, you may need to spray the clump several times before all of the root system is destroyed. It is a big job but I am sure over time, you will succeed.