About 3 years ago, I asked Toronto Master Gardeners if it was possible to use boxwood standards in the summer in cast iron urns and then plant them over the winter in the ground. This process would be repeated on a yearly basis. This has been very successful. Now I am wondering if the same can be done for hydrangeas such as fire and ice.
My purpose is to provide a privacy screen on my rear deck for me and my neighbour that leafs in late spring and lasts into mid fall. I prefer a plant that is bushy and flowery and can be maintained to about a 5 to six foot height.
While this strategy has worked well for the boxwood, it is a much slower growing plant. This time the hydrangeas would be planted in the summer in wooden boxes planted on the deck. Would the necessary pruning of the branches and roots be tolerated by the hydrangea? Thanks
At its maturity Fire and Ice Hydrangea is about five feet, so it is on the small side of your preferred size range. With regular care and pruning, its life span is about forty years, in the ground.
Hydrangeas can be a happy container shrub, it has a medium growth rate and maintenance includes correct pruning time, which varies depending on variety.
The hydrangeas, if established and in large, solid and thick wooden planters in a shielded area, should be fine to remain in the planters: prior to first frost, carefully cut away old wood at the plant base. Wrapping the stems with burlap and adding a generous mulch around the root area will help protect them. Our winters are particularly harsh and surrounding the plant with wire cage and filling with lightweight mulch will protect flower buds and must be carefully removed after last frost, so as not to damage buds. Even with all these steps, conditions are not optimal and there are no guarantees your plants will be happy, depending on our winters.
Hydrangea arborescens (Annabelle) and Hydrangea paniculata (Quick fire) are hardy varieties to consider: Annabelle gets to be 4-5 ft tall, while Quick fire reaches 6-8 ft.
If you are considering several 5-6 foot plants, then overwintering indoors is not really an option, unless you have an unheated, yet insulated garage, so a fairly intensive protection plan must be in place. Transferring several large plants into the ground is an option but is also quite labour intensive and disruptive to the plant.
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An additional consideration: for a low care privacy hedge that remains full year round, Juniper, Yew and other evergreens can survive well in large insulated wooden containers for winter. Yew notably is tolerant to harsh winter, looks great and full year round, with female plants showing pretty red berries in autumn. It is low care and can be happy in a a range of soil types (just not overly wet) and exposure conditions, including shade.
It seems that using properly insulated outdoor containers for container plants and keeping them outdoors, is the more successful route.
Either by sinking the pots themselves into the ground in an all weather, non-decorative container or by using large insulated containers that the plants can remain in for the winter.
Your nursery should be able to suggest planters suitable for this and additional foam insulation if needed, depending on the size plant and container.