Unfortunately
you are not the first to find this problem when growing in containers. I am
somewhat amazed that the cannas could receive enough water and nutrients to
produce this growth in your container. You must be doing something right. Do
you happen to know which canna cultivar you are growing and how many
plants/rhizomes did you plant in each container?

In your lengthy
growing area, cannas typically need to be divided, thinned and replanted each/every
spring. A 22” container needs to start with only one or two small healthy plants in
the spring. The container may look bare to start but good plant or root stock
will easily fill this container and reach its full potential each year.

The choice
of cultivar and container size will often be a determining factor in successful
results.

Because many
of these containers can be expensive I would recommend removing the rhizomes
however you find suitable. Do not be concerned about cutting or damaging the
rhizomes. You will likely find that most will survive the surgery and you will likely
have more pieces than you need to replant. In fact, your biggest problem is the
removal and what to do with the excess rhizomes.

Good luck
and let us know how things work out.

Kent

Thanks for the reply. Dunno what the cultivars are - just bought a bag from Home Depot - the flowers are orange. I put in two rhizomes per container. The Hummingbirds seem to love them. During the warmer months I would hand water daily and mix in liquid fertilizer every two weeks. Really the only problems are that when it gets windy, the containers tip over since the shoots are so dense which is one of the reasons why I bought some 30" containers with wider bottoms that I was thinking to repot in. However the rhizomes are so dense that I should be able to get at least 50 pieces per container with a shoot. Since I can't see the roots I have no idea how dense they would be. I thought about using a spade but the rhizomes are so dense that I think I will have to use something a lot bigger and deeper that I could cut into them (like a shovel). How long should I let the cut rhizomes dry before I replant?

I am sure
you will find the feeder roots to be very dense and intertwined. Do not worry
about removing these. Your replanted rhizomes will produce new ones. You can
salvage some and leave them attached where possible (if they are still fresh
and white); not a problem either way.

Assuming you
will be repotting soon and there are open wounds, I would only allow a day or
two to help the wound seal. We often lift/divide and replant the same day. Cannas
do not require a hibernation period. Folks needing long term storage would
likely choose to place the rhizomes in a container covered with slightly moist
peat to prevent excessive dehydration.

Healthy
canna rhizomes are very resilient. Please consider not overcrowding your
containers and dividing/replanting each and every season.

Best,

Kent

Wow, that was quite a struggle and after only one container I'm exhausted. The first 4-6 inches were nearly solid rhizome so a spade would not work well. I tried a shovel but couldn't get enough weight for it to go down past the rhizome area (the container would tip over if I tried to stand on it, so I ended up using a mallet on the spade to drive it down). I even found new white shoots as far down as 8 inches (dunno where they were supposed to come up since it was solid rhizome above it). The last 4 inches at the base was a solid white block of intertwined roots.

The sheer volume of rhizomes I have now is well over a 100 times the volume of the two small ones I planted two years ago. It's too bad this isn't ginger (although the rhizomes look a lot like ginger) which I use a lot and can be quite expensive certain times of the year. I've tried growing ginger here but never had much success.

I'm retired and part of the reason for taking up gardening was for health reasons. So dividing and replanting every year is probably a good thing for me right now. As I get older though, it will probably be too much for me.