Hydrangea Hero Wanted

Sorry to contradict, but I would try to tease the roots away from the bottom of the plastic pot and remove the pot completely as it will only act as a barrier for future root development if you plant it attached. If you have to use secateurs to prune some of the roots, don’t worry, the plant won’t come to any harm, as long as the main rootball is intact those smaller roots will regenerate. I saw some Hydrangeas at a couple of local garden centres this morning. At £20, for the size, yours is a reasonable buy. Keep it well watered in a shaded, sheltered location and it should establish well. That pruning information you received from the supplier is still not correct.