I recently took up Canna gardening, and started with a few small purchases from the USF Tropical Fair, supplemented by about 14 tissue culture plants from Florida Hill Nursery, all of them, about the size of yours.

Give them a good compost/manure mix, water daily, and provide them as much sun as possible.

Don't be alarmed if you see a leaf or two die along the way, as I'm finding they'll 'burn' through leaves quickly, while adding inches to their stalks, and sending up pups around them.

It's tough to say if they'll flower this season, but if it stays warm here (I'm in Pinellas) till October/November, it's definitely a possibility.

Lastly, don't trim them down unless a particular stalk has flowered. Once a stalk flowers, it's not going to grow further. At that point, trim the stalk back to the base, but leave the rest of the plant alone.

The roots or tubes that I received had anywhere from 8 to 12 inches of the plant above the root or ground level attached. I have since trimmed all back to just a few inches above the soil level. One plant, smaller stock, had new growth up through the middle and is probably over a foot tall now, just about to form leaves. I checked the rest and I see two sprouts forming on two of the plants. I had been keeping them in the garage but have since started putting them outdoors.