Blooming hydrangeas
Endless Summer is a newer variety of hydrangea that continues to bloom during spring and summer.
Photo by Barbara Smith/Clemson Extension
Hydrangeas get a lot of love in South Carolina, where old-fashioned bigleaf hydrangeas dot landscapes from the mountains to the coast.
Few flowering shrubs deliver a summer impact like bigleaf hydrangea (Hydrangea macrophylla). I have a sentimental attachment to this most traditional of hydrangeas from childhood memories of family members’ gardens. Thanks to their ease of rooting and transplanting, they were easily passed down and shared with friends and neighbors.
Hydrangeas also offer us that rarest of flower colors—blue. Flower color on bigleaf hydrangeas, including both mophead and lacecap types, can vary from deep blue to greenish white to bright pink. It’s not unusual for a gardener to be gifted a piece of a blue-flowering plant, only to have it flower pink in their own garden. The reason for that is all about how the hydrangea relates to the soil it’s planted in. Blue flowers bloom on hydrangeas growing in acidic soils (pH 5 to 5.5) when there is sufficient aluminum content. Aluminum is the linchpin for producing blue flower color, but hydrangeas can’t absorb it at higher soil pHs. So, in less-acidic soil (pH of 6 or higher), or when aluminum is lacking, the flowers will trend toward pink.
Excessive amounts of lime or other nutrients, particularly phosphorous, can interrupt aluminum uptake, leading to pink instead of blue flowers. If you want to know why your hydrangeas are blooming blue, pink or somewhere in between, a soil test will help you find the answer.
If pink flowers are your goal, add lime according to soil test results. Many S.C. soils naturally produce blue flowers; if yours does not, your soil report may recommend adding aluminum sulfate, a granular product that lowers pH and supplies aluminum for blue flower development. Be cautious: Aluminum is toxic to many plants at high levels, so don’t apply too much aluminum sulfate.
Besides flower color, failure to bloom is the biggest concern I hear from hydrangea gardeners. The old-fashioned varieties that bloom only once, in spring, flower on “old wood,” meaning their flower buds form during late summer and fall of the previous year. Heavy pruning between fall and spring removes those buds, reducing or eliminating the spring show.
A late freeze, after plants begin to leaf out, can also kill the buds. You can try to protect them by draping a cloth sheet or burlap over them when a late freeze is forecast. It’s not a guaranteed safeguard, but it’s better than nothing.
You can, however, protect young buds by managing your pruning. For dormant pruning, remove dead stems and flowers in early spring, just as buds begin to swell. Remove any branches or branch tips that don’t show swelling buds, but leave healthy buds in place to preserve the future flowers they contain. If you need to reduce plant size, prune just after the blooms have faded.
The newer, remontant (a fancy word for reblooming) hydrangea cultivars, like Endless Summer and Penny Mac, flower on “new wood” and are more forgiving. Even if you cut off spring flower buds or lose them to frost, new ones will take their place for a later bloom.
There’s a dizzying array of hydrangea types and varieties, including the traditional mophead look or the lacecap hydrangeas, like Blue Bird. A hydrangea that fits nicely into a more natural landscape is the Southeastern native oakleaf hydrangea. Snow Queen and Alice are popular cultivars.
Hydrangeas like moist but well-drained soil, with morning sun and afternoon shade, to protect them from intense summer heat. Water the soil underneath shrubs early in the morning, or use drip irrigation once a week or when wilting is first observed. Give them a general-purpose, slow-release fertilizer in spring as new growth emerges, then supplement with nitrogen as needed. Don’t fertilize after July.
Don’t forget to snip some blooms to enjoy indoors. Hang them upside down to dry inside, then create dried arrangements to prolong the show.
S. CORY TANNER is an area horticulture agent for Clemson Extension based in Greenville County. Contact him at shannt@clemson.edu.
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Get More
For more on growing hydrangeas, see Clemson Extension fact sheet HGIC 1067.
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