Cutting most bigleaf hydrangeas to the ground in fall effectively removes any potential for flowering the next summer!! The vast majority of these bloom on growth that was produced the previous season and removing that growth (woody stems) removes any latent flower buds that are present now and will produce next season's show. It is my recommendation that these types of hydrangeas NOT be pruned or pruned as little as possible. Removal of any dead wood in spring is fine.

These latent flower buds are very vulnerable to winter cold damage as well so in zones 6 and below, these shrubs should be covered/protected for the winter. I've linked to a search on this forum that addresses winter protection - select the method you prefer but DO cover and DO NOT cut back!!