I bought these climbing hydrangeas 3 years ago. This is the first year they start flowering. My goal is to train them to climb onto the wooden trellis (see attached photo). So far they have been slow to attach themselves to the wooden trellis. Any suggestions to help with this process. Would pruning help them to grow more vertically?
Thank you for contacting Toronto Master Gardeners.
New plants can take time to establish themselves. Often the first year can be spent creating sturdy roots systems. Climbing hydrangeas are known to be slow starters so hopefully now you are on your way with your first flowers.
Climbing hydrangeas, Hydrangea anomala, like partial/full shade but can tolerate some sun. They are tolerant of drought and should have well drained soil. You could mulch around the base of the plants with wood chips ( not bark mulch). The mulch will absorb water and maintain moisture in the soil and control weed growth near the vines. The mulch will also breakdown over time and add nutrients back into the soil. Make sure the mulch does not come in direct contact with the vine as you do not want to maintain moisture on the stem’s woody structure.
You can prune for shape and to encourage the vine to grow in certain directions though yours are still small and probably do not need too much cutting. You will also need to tie the branches to the supports to help guide it upwards. Make sure the ties do not impinge on the thickening of the branches. If you do prune, prune right after they flower so the plant has time to grow and develop next years buds. Do remove any damaged or dead wood when you find any. You can also leave the flowers on as they do last awhile then go on to add some interest to the winter garden.
You may find as the plant grows it will be a bit too heavy for the lattice you have at the moment. The trunk and branches will develop into quite substantial limbs. You may want to consider a sturdier structure as the plant may pull over what you have at the moment.
The following link has further reading on climbing hydrangeas.