Generally, training a paniculata into a standard or tree form begins quite early, when the plant is little more than a tall seedling - I have no idea how successful you will be with a plant that already has some maturity and size to it, but it could be worth a try. Or you may want to try some from cuttings of your existing shrubs - this may be a more successful approach.

You want to select a stong stem that is growing vertically or nearly so and as straight as possible and remove all the others. Staking is probably a good idea until the branch/leader has developed some girth and structure and becomes self-suporting and that could take time. You want to remove any lateral shoots that may emerge along its length except for any terminal growth. Terminal growth should be allowed to develop unchecked as this will be needed for the photosynthesis required for the plant to convert energy and nutrients into food. Gradually, the lowest terminal growth is removed until the stem has extended to the desired height, forming your trunk. The canopy can then be shaped as desired.

This is a process that takes a number of years to achieve. Commercially grown tree-form hydrangeas are at least 5-6 years old, often older depending on size and the training and pruning is pretty consistent throughout this time period. That is one reason why tree hydrangeas typically have some hefty price tags associated with them compared to shrubby ones - you are paying for the additional time it takes to get this plant to a marketable size and for all the considerable hands-on effort of the grower.

An alternate method that may be more appropriate for already established plants such as yours would be to select several (3 or other uneven numbers are suggested) of the strongest and most upward growing stems and focus your attention on them. Remove all the other stems at ground level and again, continue to remove all lateral shoots that emerge from the framework stems until you have achieved the height you want. You won't exactly have a tree per se with this method but you will have most likely get a taller shrub with a much more tree-like appearance. Again, I'd suggest staking with this method as well as the flowerheads will weigh down the branches until they reach a diameter and woodiness to be self-supporting.

Thank you for giving me a couple of options.

I read that all paniculata can be "treeified" but do some tend to do better i.e. are stronger than others. In Paniculatas I have a pink peegee, white diamond, bombshell, limelight, quickfire, angel's blush and vanilla strawberry. I'm leaning toward "treeifying" the vanilla strawberry, limelight, quickfire and pink peegee because they are sheltered more from winds and the white diamond because it's branches seem so much more sturdy. Ideas, thoughts....how would you pick? Thanks in advance hydrangea gurus. Amy in Utah

H Kel, cut back 3yr old VS was crowding out my ES. Tied back weaker branches