Whether on a wall or fence, Goodspeed says the plants need some type of support to help them maintain their shape. This is especially important when the plants are young. Remember that most plants are stubborn, and it takes a good strong wire or fence to get them to conform to the desired shape. This helps establish the framework. He suggests tying branches loosely, making certain they have room to grow and expand.
Tight wires can easily girdle and kill a branch.
Move ties every three to four months to make sure they are not restricting growth on the branch. Twine tied loosely, or twist ties, like those used to tie garbage bags, work well. Once the plant starts to grow, shape it every month or two. Remove branches or twigs growing out of place, and retie stray branches. Spring is a good time to do major pruning.