June Shrub of the Month-Big Leaf Hydrangea

Even if you aren’t a plant-geek, it’s impossible not to notice-those shrubs brimming with huge blue or pink blooms, like a set from a Hollywood movie. You know the one…there’s a big Victorian house with a wrap-around porch, and two or three ladies with wide-brimmed hats are sitting on a porch swing, sipping lemonade and complaining about the heat. And surrounding that porch and those ladies are flower beds overflowing with big leaf hydrangeas in full blue or pink glory.

That image is what most people envision as they plant their big-leaf hydrangeas, Hydrangea. macrophylla in St. Louis. Sadly, they are disappointed the following spring when they have either no blooms or a measly one or two.

Now, you have two things to complain about as you sip your lemonade on the porch in the heat.

Big leaf hydrangeas, Hydrangea macrophylla, are not just Southern Belles; they are Southern Divas, but without the charming twang.  Not enough water, they pout and wilt; too much alkaline in the soil, they turn pink instead of the coveted blue; too much sun, they go crispy; and if it’s too harsh a winter, they refuse to bloom for you.  

First, The name says it all: HYDRANGEA. “HYDRO” means water. Do not let them dry out. They will be the first in your garden to let you know things are too dry.

Second, that pink and blue thing…well, it comes down to pH … sort of. It’s actually aluminum sulfate that causes the flowers to turn from pink to blue, but your soil’s PH is what makes that aluminum available to the plant. More aluminum usually means a lower PH and bluer blossoms. Less aluminum means more alkaline and pinker blooms. A PH somewhere in the middle means pinkish, lavender, or even a mix of the two on the same bush.

Third, that winter thing…the plant tag and online references say it’s hardy to zone 5-what the heck!?!? The plant is hardy, yes; however, big leaf hydrangeas flower on old wood—the buds form the previous year, wait all winter, and then bloom in spring. If we get harsh temps, it might kill the flower buds, but not necessarily the stems or the entire plant. Other hydrangeas, such as H. paniculata or H. arborescens, flower on “new wood,” meaning they form their flower buds in the same year they bloom, thereby eliminating this problem.

Enter the ENDLESS SUMMER hydrangea series with the promise of blooms every year since they bloom on both new and old wood. It sounded like the perfect hydrangea! But this is St. Louis, and so no, even ENDLESS SUMMER will not bloom every year here, not without a lot of protection.

Big leaf hydrangeas do require more water than any other hydrangea if not any other plant in your garden, so site them well in the garden. Afternoon shade is a MUST, and if you can find a sheltered spot that will protect them from winter winds, you might get flowers every year, but it averages about every 5-6 years here in the Lou and surrounding areas.

No matter, we still love them and still dream of those summers filled with big, blue blossoms and lemonade. This year, we got them. Enjoy.

What I love about this plant;

-STUNNING flowers in pink or blue, mops or lace cap. Read your plant tags and research before buying.

-Old-fashioned shrub that has a sentimental spot in many hearts.

-Makes great cut flowers or can be dried for arrangements.

What’s not so great;

-Quite the diva in the garden, needing lots of moisture, shade, and winter protection.

-Bud blight, bacterial wilt, leaf spot, mildew, and aphids can be issues.

-As a general rule, if you want blue flowers, your soil will be alkaline; if you want pink flowers, your soil will most likely be acidic. You can have fun with Miracid and other treatments, but my favorites are those that bloom in between blue and pink. They are lovely in themselves like cake icing flowers.

-Pruning at the wrong time is another common cause for no flowers. Any pruning should be done right after peak flowering time. Pruning in the fall, winter, or spring will cut off flower buds.

-They are the most unreliable hydrangea bloomers due to flower buds forming on old wood and getting zapped in harsh winters. If you would like blooms every year instead of only every 5-6 years, try one of the other hydrangeas, such as the panicle or smooth hydrangeas, which flower reliably and are tough as nails:

July Shrub of the Month-Annabelle Hydrangea

September Shrub of the Month-Little quick fire panicle hydrangea

-Comments or questions? Email Garden-Lou at gardenloustl@gmail.com

Words and photos by Jo Batzer

© Jo Batzer, garden-lou.com-2025, All rights reserved.