I planted two climbing hydrangea 3 years ago in 2 large containers (36"x12x12) on my balcony facing south. They are healthy and this year has started producing flowers. The problem is training them on the trellis (see attached photo). So far none of them seem to attach themselves to the trellis. The containers are right up against the metal railing. There's a small gap between the metal railings and the upper glass wall. The trellis is attached at the top to the glass wall on either side but not attached at the lower end. The lower end of the trellis is about 6" above the bottom of the glass wall. Do I need to attach and secure the lower end of the trellis to make it more stable and secure? I am wondering if I need a better and bigger trellis? The plants seem to know there's support on the window side as there's where most of the new growth occurs but yet they are just not attaching themselves to either the trellis, the window wall or the metal railing.
You may need to help them attach to the structure.
These articles will help you.