Pond plant

[Thunderbird+]

Last year I planted a Pickerel weed (pontederia cordata) in my pond on a high ledge with a couple of bricks undernieth to bring the rim of the pot just above the water. Everything else in the garden is growing like wild fire! but no signs of life from this pot yet, I'm begining to think now its dead, maybe killed off by frost. I just wondered if anyone else has this plant and if so, is it showing any signs of life yet or do i need to be a bit more patient. any advice welcomed Thanks