Can hardy hydrangeas in elevated deck box planters be removed from the planters for overwintering in-ground?
- after frost in spring, will it harm bud or root development when the plants are returned to the deck boxes?
- is there a suggested root ball pruning maintenance plan (size of ball, best time for pruning, etc)?
Hardy hydrangea varieties can be sunk in-ground for overwintering before first frost. This should not damage the plants for their return to their deck planters. The plants can be put into non-decorative planters, which some find makes it easier when extracting the plants in spring – or be left as is, when being transferred in-ground.
The plants ideally should be transplanted while dormant but before frost and ground freeze. As the roots are fibrous and form a dense ball, one needs to obtain as much of the ball as possible. The location should have well-drained soil, morning sun and some afternoon shade and once planted, they will need a deep watering.
With regard to pruning the root ball, in spring when returning to their containers, the guidelines are much the same as with the boxwoods, with which you have had success. In the spring, inspect the ball and soil around it for damage and prune as necessary – you may also want to gently loosen the area around the roots, if you find compaction.
For excellent further reading about caring for hydrangea: