Put it in a big pot with a 50/50 garden soil & compost mix. Put pot in shade to semi-shade and protect from excessive wind. Water well and regularly. If you like, after a few months dose with a hydrangea colour fixer as flower colour depends on ph of soil and can be adjusted. Feed once a year with ordinary general fertilizer. Cut back hard after each flowering season. Hydrangeas are fairly tough little buggers so can cope with a bit of neglect but do need protection from too much sun and do need enough water. Some snail bait is a good idea while it's getting adjusted to its new living conditions. Great patio plants if protected from too much sun.

I have no specific advice, but a previous landlord whippersnippered a hydrangea to about 2 inches tall and it recovered. Hardy beasts.