The two most popular species are the H. arborescens and H. paniculata. The other two main species are H. macrophylla and H. quercifolia. The lesser known species are H. serrata and H. anomala.
H. arborescens is known as the smooth hydrangea and has cultivars that have incredibly large blooms that can be as big as a basketball.
The species is native to Ohio and is commonly seen in many of our natural areas in the Miami Valley. The flowers on the species are not as spectacular as the cultivars and you will find this in complete shade in many cases.
Cultivars such as Annabelle (one of the early ones developed), Invincebelle and Invincibelle Ruby, Incrediball all have large flowers and are either pink or white to cream colored. Some of these start blooming in early June and continue through the summer.
H. arborescens are quite hardy and grow to around 3 to 5 feet tall. They can be pruned in the spring as they bloom on new wood.
H. paniculata is a popular species as there are numerous cultivars on the market today and more are coming out each year. This grows anywhere from 2 to 15 feet depending on the cultivar.
These blooms can be quite noticeable as well and the blooms are shaped more like a pyramid rather than a ball. They also bloom on new wood and can be pruned in the spring or fall.
Popular cultivars include Limelight, Little Lime, Pinky Winky, Vanilla Strawberry, Little Quick Fire and many more. These start blooming in late July and go through the fall.
The oakleaf hydrangea, H. quercifolia, blooms in early June and is usually whitish to ivory with panicled or pyramid-shaped blooms.
These can get anywhere from 4 to 9 feet tall, depending on the cultivar. One of the most common cultivars is Snow Queen and a shorter, more compact cultivar is Pee Wee.
This hydrangea has beautiful maroon fall color and retains its leaves for quite a while in the fall. I never prune these, but if it needs it, do it after blooming.
The final group is the H. macrophylla or smooth hydrangea. These have the blooms that everyone wants to turn blue.
The blooms are normally pink in our alkaline soil; to get the blue blooms, you must change the pH to acidic. Note, this is a big challenge on our limestone soils and is a continual process.
In addition, they are supposed to bloom in the spring on old wood and again in the summer on new wood. However, they tend to have a lot of winter dieback and only bloom in August.
Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at firstname.lastname@example.org.