Spring flowering plants should be divided after they have finished blooming. Divide irises in July, poppies in August and peonies in September. Perennials in patio containers should be transplanted into the garden 2 to 3 weeks before freeze-up. In late fall, water plants heavily before the ground freezes. This is done with the use of insulation.
Snow is the best insulation.
It also provides moisture. Only pile soft snow over plants and flowerbeds that are under house overhangs, close to house or under eaves or any place where snow disappears. DO NOT use packed snow from walkways and driveways nor snow which contains salt or de-icer. Mulch is the next best thing to snow. If using evergreen boughs use 2 layers at right angles to each other.