I would like to plant a hydrangea tree. I have read that the best times to plant are early spring and fall. Since we are already coming into summer and the weather here in the Niagara Peninsula is hot and humid, is it still possible to plant at this time? My garden has been recently torn up and is empty and needs plants and I don’t want to wait till fall to plant. Would appreciate any advice you can give me. Thank for your time. Lina
Thank you for contacting the Toronto Master Gardeners. Southern Ontario has experienced unseasonably hot weather in the past week but it is not too late to plant your hydrangea tree. Traditional wisdom has been to plant trees in spring or fall. But now that trees – especially smaller, ornamental trees and shrubs, come with good root systems in plastic pots, summer planting can also be successful. Hydrangea paniculata comes in several cultivars. I have attached some information about one of them here Hydrangea paniculata- ‘Lime light’. They can be trained into a single stem or grown as a multi-stemmed shrub. This plant will grow in sun or shade but will bloom best with at least 4 hours of sun daily. When planting in hot and dry weather, ensure you provide lots of water for your hydrangea. They love water but need good drainage as well.
Recommendations about planting trees and shrubs are evolving and incorporating new research findings. Begin by preparing the hole in the new planting space. A general recommendation is to create a hole 2-3 times the width of the tree’s root ball, and as deep as the root ball. The hole should be saucer shaped. Create a mound in the centre of the hole to support the root crown. Landscape Ontario’s Tree Planting Guide has a good diagram of what the hole should look like on page 43 Tree planting guide
Conserve the soil you remove when digging the hole to add back when planting. Unless the soil in your new location is of very poor quality, there is no need to add amendments. Research shows that trees and shrubs planted in the native soil of their planting location will establish roots better and grow more vigorously. You can read more about this here: Soil amendments.
If you can plant your tree on a cloudy, cooler day or in the early morning or later afternoon, this will help to decrease the stress of hot, scorching sun. Inspect the root ball by hand to look for damaged or defective roots and prune them away. If the roots are matted together or encircling each other, this is called being pot-bound. Gently separate and spread the roots out.
Now you can position your tree in the prepared hole. The tree should sit at the same height in the new hole as it did in the pot. Ideally, the root flare (where the stem / trunk transitions to the root system), should be at ground level. Roots transplanted too deeply can suffocate or may circle the stem, called girdling, which will shorten the life of the tree. Planting above grade level will cause the shrub to try out faster, make it less stable and more prone to frost heaving.
Refill the hole with the native soil you dug out to create it. When hole is about 2/3 full, water well to help the soil settle and remove air pockets. Continue to fill the hole and water again. You may want to apply an organic soil amendment such as compost and then add 2-4 inches (5-10 cm) of organic mulch (e.g., wood chips) around the tree base but at least 6 inches (15 cm) away from the trunk/stem.
Ensure your newly planted tree gets adequate water over the coming months. This is a key to successful and healthy growth. Deep less frequent watering is better than brief frequent watering and can be adjusted based on weather conditions.
Best of luck with your hydrangea tree!