Jochen, unlike your banana plants; the individual rhizome canes (stalks) only remain viable to the plant until its reproductive stage is completed. In other words once the individual cane completes the flower and seed production cycle that stalk begins to die. Depending on the length of your growing season you will be able to observe this quite easily. The underground rhizome should continually produce more new stalks throughout the season and one usually has a number of stalks in bloom late in the season. All of this depends on the length of the Âwarm growing season. After frost or light freezing weather has killed your plant it would be best to remove all the above ground foliage and mulch the rhizomes to prevent freezing of the underground structure. Your zone would likely fall in a mild z7 or a cold z8 relative to the US. Regards, Kent.

Jochen
I have been experimenting with overwintering cannas alive for the last two winters. It does work, contrary to perceived wisdom. I only tried because of poor results overwintering the tubers. The first year they came inside 3 feet high. The next year they grew to 6 feet high and didn't flower, but the leaves were enormous. During last winter they died back to 4 feet high again, were slow to get going this spring, as was the canna musifolia, but they are now 5 to 6 feet high again, with no sign of a flower.
I over winter them in an outhouse/conservatory that has plenty of light and a minimum temperature of about 5 or 6 degrees C. I bring them in before the first frost, and treat them for vine weevil and remove anything hiding amongst the leaves. Light watering is occasionally required during the winter.
I don't mind the lack of flowers as the huge foliage is a good exchange. They stand next to the canna musifolia, which is a big brute that reaches 8 - 9 feet from scratch every year, but unlikely to flower in the UK. I wish I had the height in the outhouse to overwinter it too.
Good luck
Nik

I am in zone 9. Mine stay in the ground until I am ready to devide them. When there is a chance of frost (from 4-8 times during winter) I cover them. I get flowers all year that way. If some leaves get bitten a little thats ok with me. As long as the ground doesn't freeze the plants do fine.
Sky~

Wid will catch those huge leaves like it would catch sails, whipping them to shreds, so they need shelter from strong winds.

(I just know this.)

Nik,

Thank so for that, IÂll give it a shot. Would love to be able to get more height and as with you I donÂt mind if they donÂt flower seeing that the foliage is wonderful to look at as it is.
Although theyÂll be living in the shed for the winter, but I am sure that IÂll manage the temperature somehow,.

Jochen

Sylvia
You're right about the wind, mine suffered more from broken stems until I got the shelter sorted.

Jochen
I've tried overwintering them in an unheated garage. Even though it doesnt get below zero in there, they didn't stay alive and green, but they did throw up new shoots in the spring. You could try wrapping them in straw and fleece in the shed. I doubt that wrapping would work outside, as much below 5C seems to do for them as plants and makes them go dormant.
My big mistake was to experiment with canna Indica, a boring rusty red leaf with little variation, that I didn't mind loosing. I should have chosen something more stripey. I'll try posting a photo.
Nik

Here is a link to a photo of my overwintered cannas. They are on the right. On the left are three of this years new grown ones.
http://img.villagephotos.com/p/2004-10/860039/OldCannas.jpg

Nik,

Just looked at the photo and they are great. So what I would need to do is obviously lift them out of the ground, wrap them and place in the garage or shed.
At present I have the problem that most of the leaves of my canna look like Swiss cheese since the plant was attacked by some caterpillar, also the wind is becoming a bit of an issue, but this is Scotland after all. However is there anything I need to watch out for when I lift them out of the ground? Do I need to water the plants while they are wrapped?

Jochen

Jochen
I keep mine in big pots, and just bring them in, on a sack barrow, for the winter.
To overwinter alive you would need to replant them in something. Maybe get a big pot, plastic is OK, and keep them in it for next year as well. Mine need some water during the winter as I have an extractor fan on a timer to help control the humidity. It errs on the dry side in there at times, so a little watering doesn't go amiss. The things that continue flowering, Abutillons, Daturas, Citrus etc get a bit of feed as well.
Wrapped Cannas in an unheated building would probably need a little water if they stay green ie undormant. You would need to check the plant and the soil to be sure when/if water was needed.
Funny, but I've had to pick several green caterpillers off my cannas early this year. Never had them before. The leaves look like they've been machine gunned.
I hope to have extra over wintering space available this year, so the Canna Musifolia might get in green. Heaven knows how high it would get next year.
Nik

Jochen,
I've done both: left a few rhizomes in a pot and dug up rhizomes from the garden. I treated the ones in the pot like any other house plant. They grew beautifully! In fact, they were the first things with blooms in the house. An awesome feat to my neighbors.

The rhizomes that I dug up were placed in tubs of COARSE vermiculite. The large pieces of vermiculite were not easy to find, but well worth it. I placed the canna rhizomes in layers of the vermiculite, placed the tops on and then stored the tubs in a cooler part of the house. I did nothing else-no peeking, no watering. In the Spring, I was so surprised to find all of the sprouting rhizomes!

My fellow gardeners also store dahlia tubers in the same manner and have equal success.

Good luck!

Susan