On a recent trip to Cape Cod I intended to write about the age-old question, “Why are their hydrangeas so blue?” and to review how to choose or maintain the best blues at home. What I found there was blue only in the bay – not a blue hydrangea in sight. The experts at the nursery told me exactly what industry pros in Western New York have been explaining: The winter was extremely severe; it was a long, cool spring; most plants seem to be appearing and flowering two or three weeks late. So much for photographing blue hydrangeas.

Before you start doctoring, condemning or giving up on your own hydrangeas, let’s straighten out the facts about blue flowers in case you need to adjust your expectations. Most gardeners eventually learn to recite that blue hydrangeas require acidic soil – a low pH number – which explains why the somewhat alkaline soils in most of WNY tend to produce mostly pinkish or mauve-toned blooms. Gardeners then go about attempting to adjust the soil pH, using sulfur-based products, something that is doable over time. Or they keep dosing the plants with fertilizers labeled for acid-loving plants (i.e. Miracid), dreaming of the flower borders of Massachusetts. That’s just a short-term boost, not a solution.

Changing color

However fun the concept, you can’t change hydrangea colors like wallpaper. White hydrangea flowers will be white and cannot be turned pink or blue, no matter what you do to the soil pH. Many white flowers do change naturally as the growing season progresses, moving through shades of pink and beige, including panicle hydrangeas (H. ‘Strawberry Sundae’) and oakleaf types (H. ‘Alice’ or ‘Pee Wee’).

Hydrangea macrophylla (meaning big leaf hydrangeas), which includes both mophead and lacecap type flowers, is the playground for changing flower colors. Even in these versatile plants, color changes can only go so far and some plants tend toward pink or blue tones even when pushed in the other direction. ‘Glowing Embers’ and CityLine ‘Paris’ and ‘Vienna’ tend to stay pink even in acidic soil; ‘Forever and Ever Red’ is inclined to be red.

If you are attempting to alter some of the more flexible types (‘Endless Summer’) it is also helpful to grasp this fact about color intensity: Flower color intensity mostly does not change. A medium blue (‘Nikko Blue,’ ‘Dooley,’ ‘Endless Summer’) might be changed to medium pink, but it will not become a deep or cobalt blue. If you want deep blue, buy one such as ‘Blaumeise’, ‘Blue Danube’ or ‘Nantucket Blue.’ And even this rule isn’t absolute.

Fred Safford of Lockwood’s Greenhouses has become a hydrangea expert in response to the public’s obsession with this genus, and he countered my understanding of the intensity factor this way: “Yes, but there are exceptions there too. Look at the washed-out pink of Let’s Dance ‘Starlight’ or ‘Moonlight.’ If you lower the pH you can get a deep, rich purple – from ‘blah’ to intense!”

Finally, if you have a hydrangea that is subject to color change, it’s all about the soil pH. Soil contains aluminum, the element that produces blue in flowers. Acidic soil permits that aluminum to be absorbed by plant roots. Alkaline soil binds up the aluminum. In most of Erie County the soil is slightly alkaline and, if untampered with, ‘Endless Summer’ hydrangeas and their color-flexible friends will tend to be pink or mauve colored. Only by acidifying the soil can you help those plants get their aluminum and turn their flowers blue. Several products are available that do this, with instructions recommending the amount per plant or per square foot of soil, but be careful because excessive aluminum sulfate can be toxic to plants.

For significant changes, repeated applications will be necessary. When in doubt get a soil pH test from Master Gardener volunteers or with a professional testing kit. In case you want pinker rather than bluer flowers, soil pH is raised by adding lime. Somebody on Cape Cod right now is probably trying to turn those darned true-blue flowers pink.

Beyond pinks, blues

As if hydrangea shopping were not confusing enough, hybridizers have been working on offering us multicolored flowers or two-toned flowers with contrasting edges (an effect called “picotee”). Consider the L.A. hybrids, multicolored with no color treatments. ‘Everlasting Revolution’ has blue, pink and purple colors simultaneously. Not to be outdone, the Let’s Dance ‘Diva’ has pink petals and blue florets.

How to choose a hydrangea when the choices are so varied? As with all plant placement, consider the site you have and what will grow well there. In general Hydrangea macrophylla – pink or blue – benefits from lots of sunshine but protection from the blasting heat of late-day sun. In general, the re-blooming types (called “remontant” ) that bloom on both new and old wood (this year’s and last year’s growth) do best with some winter protection. In general, some of the newest multicolored or gold-leafed types are slightly less hardy. Usually oakleaf hydrangeas tolerate more shade than other types.

The size you want is equally important. We used to expect panicle hydrangeas (‘Quick Fire,’ ‘Pinkie Winkie’ and ‘Limelight’) to be 6 to 8 feet tall – until somebody bred ‘Little Lime’ and myriad other shorter cultivars. The blue-to-pink subject of this column – the macrophyllas – were once expected to grow about 4 feet tall, but now we have adorable, short ones: the whole Cityline series, ‘Harlequin’ and ‘Pia’ among many others. Bottom line: Read the tags; talk with experts; read the books – and try a new hydrangea.

Yes, you can mess with some of their colors. But is it really necessary? Happiness may be finding a beautiful, generously blooming hydrangea and enjoying the color it is, growing in the soil you have. Next week, the hydrangeas at the Cape will be showing off how blue a blue can be. I expect to be celebrating my own alive, finally flowering and marvelously mauve ‘Endless Summer.’ It will be glorious!

Sally Cunningham is a garden writer, lecturer and consultant.