I bought several Nikko Blue Hydrangeas and I have heard that they get gigantic. I was going to use them as a border around my deck. I placed three of them on the one side of the deck 3 ft. apart (they are about 2ft tall). The deck is 11ft long. I am worried that it is going to get too big and out of control. I have research and noticed that it is suggested not to prune because they really don't need it. Is that right? Any advice would be great.
First, there is the adage of "the right plant in the right place." When you say, "I have heard that they get gigantic." that is something you should have found out beforehand. Kind of like getting a puppy. However, there is a difference in don't need to be pruned and can't be pruned. How big will be too big for you? They will get around six feet, but the same plant in different sites will grow to different sizes, depending on how happy it is there. Do you want the border for aesthetics or could you use the screening? If you want to keep them lower/smaller, pruning each year after flowering is an option.
One suggestion for replacement is Indian Hawthorn. It is evergreen, has small pink blooms in the summer and is tough as a holly. Gets 3-4 feet high and a little wider than high.
One mistake newbies often make is to plant the shrub too close to the area they wish to screen. If a given plant has the potential to grow 6ft. wide, then why in heaven's name would you plant it 1' from a wall or deck. Make sure you leave enough space between the deck and your new plants.