Ten degrees below freezing is, pshaw, nothing to a dock. It uses its red leaves to make heat from the sun that the rest of us don’t get to feel.
Curly dock, for example, grows through ice, thick (above) or thin (below.)
And beside the ice, too.
And, heck, without ice at all, right out of the water.
For this, it helps to have a deep taproot. It’s also why I’ve been harvesting dock in my garden, for salads, for ten days now, along with spinach and corn salad and garlic chives. Ten degrees below freezing is, you see, perfect for gardening.