New Bridal Spirea

We purchased 3 new spirea. These are the large bushes that get 6' x 6'. This variety matches the older ones and are renaissance. Once they get bigger they should be filled with white bridal blossoms. We planted these along the north east side of the garden as the screen for our vegetable garden. We paid $25 each and purchased them at Plymouth Nursery. The older ones were purchase about 3 years ago and have not grown very much. I'm not certain what we can do better for them. But they keep coming back each year. My only hope is that after 5 or 6 years we'll see some more growth.