must have drain holes, unless it's a bog plant.

manicata is wasted in a pot after a year or two as it will never acheive the gigantic size it's capable of in the ground, and I think it has no chance of overwintering outside in a pot in your area.

They don't mind thier feet wet a bit and grow largest situated next to a constant water source that they can tap....get enormous next to ponds and streams. Water the hell out of them in the summer.

Throwing its own leaves over it in the fall is sufficient where I am, but you may need to mulch more heavily.

Gunnera tinctoria (aka Chilensis, I think) is slightly less gargantuan and a little more attractive, if you can find it.

What you might do is create an artificial bog by lining a a 2 foot deep by least 2ft X 2ft area hole with rubber pond liner. Arrange its drainage so it maintains a water level about 4 inches below the surface. Fill it with peat moss. Then plant your gunnera in a large pot and sink the pot to its rim in the soil of the artificial bog. Lift the pot after the fist light fall frost and keep it in a cool frost-free place for the winter, then resink the pot in the spring after last frost.

I, too, live in Burlington, Ontario. I have successfully overwintered my gunnera manicata through the last two winters, which as we all know had been unusually harsh. My plant is getting really big. It is now two years old. It bloomed for the first time early this summer. The largest leaves were about three feet across. I hope it will be even bigger next year. It is planted in a bog garden made from a 3x3 foot wide by 3 foot deep hole lined in rubber and punctured in a few places. To overwinter, I cover the plant's crown first with some dry peatmoss topped with a peice of rigid styrofoam insulation followed by a large pile
of dry leaves. I cover the mound with a plastic tarp. It isn't hard at all. This fall I am going to construct a box made of rigid foam insulation, which I will fill with dry leaves. M
My plant has a little shade. It withstood this summer's extreme heat quite well. I did lose a few leaves when I overfertilized, though.
Good luck!
Rick

I think rick6a has the right idea for the colder zones. The heavy protection he provides is key to Gunnera survival in that region. In time these become massive plants easily out growing regular city lots.

Cheers, Barrie.

I would like to plant A Gunnera along piece of property on a bayou in Louisiana which floods with a foot of water each year during the summer season. Would the Gunnera tolerate a foot of water on its roots for a few months each year?