These famous shrubs are not small, usually four feet or more high with a similar spread, so give them room. Penny Mac is what is called a Mophead hydrangea for obvious reasons, and the Mopheads are a group from the species H. macrophylla
which is well-known for compact, not rangy plants. But of course, the best thing about them are the colors.
Penny Mac is a newer blue, a color that is bred into the plant. But like all hydrangeas, the colors may vary a bit once you plant it. For complete information on this group of plants and how to change the color, there's a great website called HydrangeasHydrangeas.com where you can read all about it. Click here.
About Hydrangeas: These popular shrubs, also called Hortensia, all have rounded flower clusters that persist through summer and fall. There are several types, since there are several species of the plant the hybridizers work with:
H. macrophylla or French Hydrangeas. These, the most popular, form non-rangy, attractive shrubs about 4 to 6 ft. tall, and are famed for their big, colorful ball-like flowers, usually blue or pink. The popular group here is called Mophead hydrangeas. Artificially shortened versions are sold in pots on Easter and Mothers Day, and the blooms are florists favorites, always popular for wedding decorations. In addition to the mopheads (solid ball of flowers), there are also lacecap versions of these hydrangeas. (H. macrophylla is native to the Far East.)
H. arborescens, a US native, includes the widely-planted, Annabelle. Much like the Mopheads, Annabelle is a shorter hydrangea with huge rounded flower clusters in pure white. This is the one famous for flowers so large they often weigh down the branches, needing special support.
H. paniculata, is a larger species, much taller than the Mopheads. The flower clusters are more cone-shaped, rather than round. The plant in this group is more rangy than the shorter types, but can be controlled by pruning. The famous Pee Gee hydrangea, often grown as a small tree is in this group, and was imported from Japan in the late 19th century. There are also newer H. paniculata hybrids, including the beautiful greenish-flowered one called Limelight.
Other Types: There are several other important hydrangeas. The tall native Oakleaf hydrangea (sometimes considered a small tree) is also a variety of the species, H. paniculata.