I have a few of those hydrangeas and some others like below
I left them alone during winter. Now do I cut them down to the root? Or do I leave them alone like that? What to do?
I am in Pacific Northwest. Thanks
It rather depends on the variety of Hydrangea - yours look like they had rounded flowerheads, so likely H. macrophylla types, in which case, do nothing until you notice bits of green appearing, indicating growth is just beginning. In the UK that would be April; at that point, trim off all dead flower heads,remove any obviously dead stems, and trim back the the other stems to the nearest green bud or leaf break. If you cut Hydrangea macrophylla varieties to the ground, you will get no flowers this year...
Hydrangea paniculata varieties have cone shaped flowers - these can be cut down low with no loss of flowers, because they flower on new growth, not last year's.
In regard to fertiliser (if you want to do that) there is information regarding that here https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/fertilizing-hydrangeas.htm. However, if your hydrangeas don't start showing growth till April, don't fertilize in March, apply fertilizer immediately after pruning back instead.
Trim dead flowers. And remove dead limbs at this point. If when we growth starts pushing for a couple weeks feel free to trim or remove any missed dead limbs. Or trim back to active nodes if you have partially dead limbs.
Hydrangea are also very vigorous plants given conditions they enjoy so feel free to do some amount of aesthetic pruning if necessary but I would avoid cutting them to the ground.