This potted shrub has produced a superlative display. Then instead of deadheading it I actually pruned it by mistake in midsummer. Now it is taking over my balcony! What to do? There are still a few flowers – do I grit my teeth & wait until spring to cut back?
* I am not a Toronto resident, but have cancer & am desperate for help with this, please. I am happy to pay for the privilege.
The Runaway Bride hydrangea– botanical name Hydrangea macrophylla Runaway Bride Snow White (‘Ushyd0405’) — is a glorious plant, and your ownership of this specimen is enviable. The Royal Horticulture Society says that this beautiful hydrangea was bred to happily grow in containers.
It grows to about four ft. tall, and wide, at its full extent, can tolerate shade, or a little sun, thrives in containers, but needs to be watered very regularly (ideally every day). The leaves are a lovely bright green that turn brilliant red in fall. It flowers from May to October, which is amazing, and from every leaf node – terminal and lateral — not only at the end of the stem. This hydrangea guide says it is possible to have from 6 to up to 20 blossoms per stem! This variety was launched to commemorate the royal wedding (Prince William married Kate Middleton) and it justifiably won the “2018 Plant of the Year Award” from the Royal Horticulture Society in England. Since its launch, it has become very popular in England, and it is now available in Europe. For more information you can go to this website: hydrangea growing information.
However, Runaway Bride does not yet seem to be available in Toronto since it is only hardy to -15 degrees Celsius. When/if it does become available, it might be possible to grow it year round, by bringing its container indoors in winter to overwinter it: you would need to have a special, large, airy, well-lit indoor space to overwinter a four foot square plant.
Now to your problem. You have said your Runaway Bride is taking over your balcony. As you already know, this particular hydrangea grows its flowers on the previous year’s stems (old growth). Therefore, as you said, you were meant to only deadhead the old flowers and not actually prune it. Pruning this hydrangea is problematic, since pruning will affect its flowering next year.
Pruning is one of your options to making your plant take up less space, but regardless of when you prune, it will lead to loss of blossoms the following year. You could prune it now, but September is not the ideal time to prune the long shoots. You could delay your pruning to next spring which is a better time, but also with the consequence of reducing the number of blossoms. Whenever you prune, make the pruning as light as possible. Every cut will reduce the number of blossoms you will have next year. This link to the Royal Horticulture Society will tell you more about pruning of hydrangeas.
If you choose to not prune, is there a way to contain the shoots by training them either up or down? Can you raise your container onto a reasonably high pedestal and train the new shoots to cascade down so that you have a waterfall of shoots? Or can you move your container against a wall on your balcony, and place a trellis behind it? You should be able to support the new shoots to grow up the trellis so that you have a climbing hydrangea. These ideas are only possible if you are in a climate where you can keep your hydrangea on the balcony permanently.
Despite all these suggestions, finally, it is possible that a four foot square plant is simply too big for your balcony. This is a significant plant that needs a significant amount of space, and I am not surprised that it feels as though it is taking over your balcony. This may be a radical idea, but have you considered the possibility of giving it away to a friend, or to a hospital, or to another institution that has more space? It would be a wonderful gift for whomever you chose as the recipient.
If you would like more general information on hydrangeas including the different kinds and needs for pruning, please refer to this Toronto Master Gardener Gardening Guide.
I do hope this is helpful, and gives you some ideas that will help solve your hydrangea problem.