Hardiness of Hydrangea

(Question)

Hi,
I am new to Toronto. Recently I was given a Hydrangea plant
full of Blue Coloured Blooms. There was no name of the type of Hydrangea [species] The plant is about 5 to 6 inches tall. I have cut off the blooms after they faded. At the same time the plant lost nearly all the leaves. I have given it a all purpose fertiliser and see new leaf buds coming up.
Can I plant this type of Hydrangea in the ground once it has recovered? Is this type of Hydrangea winter hardy for Toronto climate? I am so sorry I can not provide its proper cultivar name.
I am learning a lot from “Toronto Master Gardner” and am very grateful for this valuable and knowledge resource.
Thank you
K.K.

(Answer)

Thank you for contacting Toronto Master Gardeners with your question about a blue Hydrangea or bigleaf hydrangea (Hydrangea macrophylla). Although there are several different species of blue hydrangea, ‘Nikko Blue‘ and ‘Endless Summer’ hydrangea are common species available in early spring at local stores. The large round blooms are called mopheads. When planted in a garden, these plants can reach 4 – 6 feet in height and 4 – 6 feet in width. Hydrangea macrophylla can thrive in Toronto which is in USDA Zone 5. Below is an informative fact sheet on overwintering hydrangea.

Climate zone info for hydrangea

Your question about whether this plant can be put into the garden rests on whether the plant in question is an Easter/florist hydrangea. Since your hydrangea was in bloom points to the fact that it was forced. Hydrangeas usually flower in the summer. Since these plants have been forced to bloom outside of their natural season they will more than likely be stressed out. Also. hydrangeas are usually not small plants. Even though the plant is now in a container, it could attain a height of at least 4 feet tall outside. These forced plants may not be as reliable as the regular potted hydrangeas which are available from a nursery.
If you want to try to grow it in you garden,  you should plant it outdoors once the danger of all frost is over. Try to remove most of the potting soil without damaging the roots. This will prevent coiling roots and allow the plant to adapt to their garden soil. You should also plant it in the shade of trees for the first year, so that the plant becomes acclimatized to its surroundings. The following spring, if it survives they can transplant it to full sun.

Controlling the colour of hydrangea is akin to being a chemist. For example, adding iron in your soil changes acidity which helps produce the blue colour. The article below gives a detailed description of how to use soil additives to influence the colour of your plant. It is possible to produce a range of pink to blue blooms on the same plant!

Chemistry Guide to Hydrangea Colour

Yearly blooms on hydrangea depend on whether buds appear on old wood or new spring wood. The Toronto Master Gardeners Guide below describes the pruning process for all hydrangea types and their proper care.

Hydrangea Garden Guide

Hydrangea are a reliable plant that can form an individual stand or an outstanding hedge. Tweaking the colour of the plant may some time and chemistry. Good luck with getting to know your individual hydrangea.