Hydrangeas have long held the eyes of gardeners and landscapers for their bigger-than-life ornamental appeal and multi-season interest. This growing season, I challenge homeowners to try their hand at growing one of the four beautiful hydrangea species that populate Central Illinois gardens. This is part two of a two-part column on hydrangea.
Hydrangea arborescens are known as smooth hydrangea and the most commonly planted cultivar is ‘Annabelle.’ It usually has large heart-shaped leaves, and equally massive summer flowers. The colors transition from green to white to brown.
In nature, this plant is loose and wild-looking, but in a cultivated setting where additional water and fertilizers are provided, it make a nice clump-forming shrub.
Flowers appear in June, and a second floral display comes in August if spent flowers are removed. These plants respond well to being cut within 6 inches of the ground. Remove the outer canes in late winter.
‘Annabelle’ grows three to five feet tall with large, round, white flowers that are six inches across. It puts on a show for six to eight weeks. Annabelle will not tolerate full sun unless supplemental watering is provided.
Hydrangea macrophylla is known as big leaf hydrangea. This hydrangea has a “rounded-mounded” habit and asserts either pink blooms in basic soil or blue blooms in acidic soils. They are your litmus tests for soil pH.
If consistent moisture is not being applied, this species needs to be grown in partial shade. There are two forms of big leaf hydrangea: lace caps or mopheads. The most common cultivars are Endless Summer, ‘Nikko blue,’ lacecap, and ‘Twist and Shout.’
It is best to prune after flowering. Sometimes even the best pruning practices can still leave you without blooms, as harsh Illinois winters can destroy stems; this is why it is best to give them somewhat of a sheltered location.
Endless Summer blooms in July, pink and white in Illinois’ alkaline soils. Endless Summer has the unique ability to bloom on new wood and old wood making the bloom more reliable.
‘Nikko Blue’ is reliant on soil pH for bloom colors. It blooms in early June.
‘Twist and Shout’ and lacecap bloom all summer long on old and new wood. They have red stems that boast red leaves during the fall months.
Aluminum causes the flowers to turn blue; however, an elevated pH can lock up the aluminum particles in the soil, making it unavailable to the plant. Lowering the pH by applying aluminum sulfate or sulfur can turn your hydrangeas blue. Sulfur is a safer bet when trying to lower pH as sulfur reduces the chance of aluminum toxicity that can occur from using aluminum sulfate.
An up-to-date soil test before adjusting your soil’s chemical composition saves money and headaches!