Miss Floribunda: In the pink, but singing the blues

Dear Miss Floribunda,

I don’t like pink. Sorry, but I don’t, and you can’t talk me out of it. My favorite color is blue, and since I moved here three years ago, I’ve admired the gorgeous blue hydrangeas I’ve seen in many gardens. A neighbor of mine rooted cuttings from her mopheads and gave them to me. I planted them around my house. They bloomed this year but are a cloying shade of bubble-gum pink, not the blue I expected. My neighbor told me that the soil along the foundation of my house must be “sweet,”and the soil in her yard “sour,” explaining that hydrangeas are like litmus paper: They have pink flowers in sweet soil and blue flowers in acidic soil. Kind neighbor shared a bag of soil acidifier with me. One dose didn’t change the color much at all, so I doubled the dose, and the hydrangeas died. She’s thrown up her hands and is pretty much done with me. What do I do now?

Moping over Mopheads on Madison Street

Dear Moping,

Although I believe all plant colors are lovely, I would never try to change your mind. I have heard that the oldest written saying in the world is the Latin “De gustibus non disputandum,” or, “You can’t argue about taste.” Consulting my old professor Dr. Wordsworth Worterbuch, I learned  that the saying is even older than I thought and was found in the ancient Sumerian language on cuneiform tablets over 5,000 years old. It seems well established that you have the right  to reject any color — or flavor — you choose.

Blue is the rarest color in the garden, so hydrangeas are indeed special. In addition, many varieties of hydrangea have a long blooming period, need little if any pruning, don’t attract pests, are easy to propagate and thrive in shaded places where not many other flowering plants will grow. A few varieties are also fragrant. Others have leaves with velvety texture or that change to beautiful colors in fall. Most mopheads (Hydrangea macrophylla) dry well for winter arrangements. 

As you learned from bitter experience, changing the soil pH is not as quick or easy as some people assume. The pH, or potential hydrogen measuring scale, indicates hydrogen availability in the soil and the level of acidity or alkalinity that influences its uptake by plants. Without hydrogen, a plant cannot take in any other nutrients, and there is a complex chemical interaction between the ions of hydrogen and those of other elements in the soil. The blue color you like in hydrangeas comes from the absorption of aluminum, the ions of which are released when the pH of the soil is low, or acidic, with a higher concentration of hydrogen. Aluminum binds with an anthocyanin (plant pigment) called delphinidin 3-monoglucoside, which imparts the color blue.

The substance your neighbor gave you to add to the soil was probably aluminum sulfate. As you found out, too much applied at once burns the roots of the plants and will kill them. You needed to be more patient, watering the soil thoroughly before applying a small amount at monthly intervals during the growing season, mulching with pine needles and leaf litter, and putting your coffee grounds or tea leaves on the plants daily. 

However, I’m not sure you could ever have changed the color of your hydrangeas from pink to true blue. I suspect that the foundation of your house is concrete, which means that lime — a soil sweetener — is continuously leaching into your soil. Your best efforts might eventually lower the soil pH to the point where most mopheads would turn mauve or purple, which I assume you would still prefer to pink.

You also could just replace the pink plants that died with white or red hydrangeas, whose colors are usually unaffected by soil pH. There are two-toned whites with red edges that are interesting. In general, the edges of white hydrangeas take on a pale green tonality if they are growing in shade (the Limelight variety is almost entirely green) and a faint rose if growing in sun. There are also many whose heads “antique” in the fall, taking on interesting metallic nuances.

What many of us call flowers on mopheads aren’t real flowers at all, but an inflorescence of  sepals, or modified leaves. What true flowers exist are hidden in the center of the bloom. The lacecap varieties, however, have prominent clusters of tiny true flowers, surrounded by sepals of the same or contrasting colors. Wild hydrangeas have true flowers, are the easiest to grow, and are always white. 

In the meantime, you can study hydrangea varieties and plan a permanent selection for fall planting. This takes considerable thought, as they come in different heights and habits and vary in their tolerance of sun and shade, heat and cold, and dry or wet places. These are considerations that have to be taken into account, along with color. Because space is limited here, I can’t go into the fascinating history of hydrangeas — they are native both to the U.S. and Asia, yet mostly developed in France — but I think you will find this worth investigating, too. 

Over time, and since you love this plant, you may well become an expert. Please consider joining the Hyattsville Horticultural Society (HHS).

Cautious plans are in progress to resume HHS (hyattsvillehorticulture.org) meetings in the fall, limited to those members who have been vaccinated.