Why your hydrangeas may go wild this year

Year after year, Marie Meiklejohn despaired over a hydrangea bush in her yard that failed to bloom.

It was not for lack of skill. Meiklejohn is a garden coach at Floral & Hardy of Skippack, and if she could not coax the showy flowers to make their late-spring appearance, who else could?

But finally this year, the bush has burst forth with crowd-pleasing scoops of pink.

“It’s blooming its head off,” she said.

She’s not the only one witnessing such bounty. Across the Philadelphia region this year, those floral dollops of pink and blue are off to the races, a trend that Meiklejohn and other plant specialists say is likely due to the weather.

» READ MORE: What makes hydrangeas pink or blue? Playing defense.

The type of hydrangeas that turn pink or blue are the “big leaf” variety, which tend to produce buds from old branches in mid-spring. If a frost or freeze occurs after those tender buds emerge, they are in jeopardy, said Erin Kinley, area coordinator of the Penn State Extension master gardener program.

“Those are very delicate little buds,” she said. “It’s going to knock them right off.”

But this year, the last freeze occurred a few weeks earlier than normal, on April 3, when the low temperature at Philadelphia International Airport hit 32 degrees, said Sarah Johnson, a meteorologist at the National Weather Service office in Mt. Holly.

Some parts of the region may have gotten a layer of frost later in the month, on April 22 or 23, when low temperatures were in the mid-30s, but generally, conditions were good for hydrangeas and other blooms of spring, said Penn State’s Kinley.

“This season in general, things are very lush,” she said.

Yet some hydrangeas still may not show their colors this year, for reasons other than the weather. If it’s one of the types that puts out new buds from old branches, proper pruning is key. The buds start to form inside the branches in the fall, so cutting them back at that point will prevent blooms from emerging the following spring — similar to what happens with misguided late-year pruning of azaleas, Kinley said.

“For hydrangeas and for a lot of spring and early summer plants, the best time to prune is right after they finish blooming,” she said. “They’ve flowered, they’re done, and you prune it back. They’ll put on that fresh growth, and they’ll have plenty of time to set buds for next year.”

When the plants bloom, yet another common question is what makes them blue, pink, or purple. Two key factors are the acidity of the soil — with a pH below 7 generally yielding a bluer tint — and the level of aluminum, the third-most common element in the earth’s crust.

It is complex chemistry, but the end result this year is simple: an especially vivid burst of garden splendor.