Pruning won’t keep a too-large plant under control. It’s best to choose the right-size shrub at the start. Some shrubs, like azaleas, are on the small side, growing 2 to 4 feet high. Spirea and oakleaf hydrangea are among the midsize shrubs; they can reach 4 to 8 feet in height. Some, like lily-of-the-valley shrubs, grow 9 to 13 feet high and are best for privacy landscaping.