Changing Hydrangea Colors

Turning Rhapsody Blue to Purple or Pink

Let's Dance Rhapsody Blue hydrangea
Moderate amounts of aluminum in the soil pH can make Rhapsody Blue purple. David Beaulieu

Don't let a name fool you when it comes to hydrangeas. The flowers on Let's Dance Rhapsody Blue aren't necessarily blue. Depending on how you care for this bush, it could be a pink or a purple hydrangea.

  • Botanical Name: Hydrangea macrophylla Let's Dance Rhapsody Blue
  • Common Name: Rhapsody Blue hydrangea
  • Plant TypeDeciduous shrub
  • Mature Size: 2 to 3 feet, with a similar spread (a size that qualifies it as compact)
  • Sun ExposurePartial shade
  • Soil Type: Well-drained, moist, and rich
  • Soil pH: can be alkaline, neutral, or acidic, depending on desired color
  • Bloom Time: June to August
  • Flower Color: Variable
  • Hardiness Zones: 5 to 9
  • Native Area: Species plant native to East Asia

Breaking down the full botanical name, the first part (in italics) is the genus and species name, and it tells us that this plant is one of the so-called "Bigleaf hydrangeas." The second part (in bold) is the series it belongs to, as dubbed by the plant developers who brought us this and closely-related new bushes. Finally, "Rhapsody Blue" identifies this particular plant in that series.

How a Hydrangea Changes Color

Like other members of the H. macrophylla species, flower color is variable for Rhapsody Blue hydrangea, despite its name. It varies from pink to blue (with purple standing in between the two extremes). Coloration will depend on the presence (and quantity) or absence of aluminum in the soil, in conjunction with soil pH:

  • More aluminum turns the sepals blue
  • A little less changes them purple
  • An absence of aluminum makes them pink

As horticulturist, Tim Wood points out, aluminum is made more accessible to plants in acidic soils. So aluminum may be the doorway to changing hydrangea color to purple or blue, but it is soil pH that holds the key to the door.

What all of this means to you, the grower, is that, if you'll be striving for a particular color, you'll need to learn the pH of your soil. You can perform a soil test using a kit (easily obtained from a good garden center) or send in a sample of your soil to your local cooperative extension and have them do the test for you.

Secondly, if you desire your H. macrophylla to be pink, your soil will have to be alkaline. If you need to make an acidic soil alkaline, as one Master Gardener suggests, "Add dolomitic lime, to raise the soil pH to about 6.0 to 6.5." She warns, however, that raising alkalinity to higher levels than that could have negative consequences for your garden.

Thirdly, those who wish to change hydrangeas to purple or blue will need to make their soil more acidic (if it isn't suitably so already) and must ensure that it contains a sufficient amount of aluminum. You can accomplish both goals by applying aluminum sulfate to the soil in question in late fall or in early spring.

Achieving the desired color often takes some foresight and some patience. For example, the first year you grow Rhapsody Blue hydrangeas, the flower color may be pink. If you apply aluminum sulfate to the soil in November of that year, then, the following year, you may end up with purple flowers. Future applications will eventually result in blue flowers, all else being equal, if you continue to apply aluminum sulfate.

There are many groups of hydrangeas, and it's generally only the H. macrophylla group that allows you to experiment with color in this way. Examples of hydrangeas with fixed coloration (their color is what it is, and no amount of monkeying around with the soil will change that) are:

  • PeeGee (Hydrangea paniculata): white
  • Invincibelle Spirit (Hydrangea arborescens Invincibelle Spirit): reddish-pink
  • Incrediball (Hydrangea arborescens Incrediball): white
  • Oakleaf (Hydrangea quercifolia): white
  • Climbing (Hydrangea anomala ssp. petiolaris): white

It's a myth that, if you place pennies around a H. macrophylla bush, it will turn the color of the flowers to blue.

Mophead Vs. Lacecap Hydrangeas

Rhapsody Blue hydrangea belongs to the group classed as reblooming hydrangeas. The H. macrophylla species is made up of two groups, the mopheads (sometimes called "hortensias") and the lacecaps, terms that refer to the appearance of the flower heads; Rhapsody Blue hydrangeas are mopheads. They can be used in landscaping as specimens, as edging plants, and in mixed shrub borders. As for all hydrangeas, what's showy on the flower heads (corymbs) of these shrubs are called, technically, "sepals" (not petals).

You may be familiar with the idea that some bushes flower on old wood, while other shrubs bloom on new wood. But some kinds of hydrangeas fall into both of these categories. And there's even a fancy name for this phenomenon: "remontant." These kinds of hydrangeas flower the first time around on the prior year's growth, then rebloom later on the present year's growth.

It's a nice bonus, obviously, to have a shrub rebloom for you. The more color you can achieve in your landscaping, the better. Those of us who bother with planning sequence of bloom will certainly value the added color. Along with growing long-blooming perennials, selecting shrubs that rebloom aids us greatly in realizing our goal of continuous color in the yard.

Let's Dance Rhapsody Blue is one type of reblooming hydrangea. Wood mentions Endless Summer, Let's Dance Moonlight, Let's Dance Starlight, and Forever and Ever as other reblooming cultivars. Michael Dirr, in making his own list of hydrangeas in the reblooming class, notes another member of the Let's Dance series, Big Easy, while also listing the following members of the Forever and Ever series:

  • Double Pink           
  • Original
  • Peppermint 

Growing Tips for Rhapsody Blue Hydrangeas

Grow them in a moist but well-drained soil. They will wilt easily during hot summers if they receive too much sun.

Wood warns against fertilizing with phosphorus if you seek to change color to purple or blue on these hydrangeas. He explains that if the soil is high in phosphorous, the aluminum that you need for the purple or blue color won't be available to your bushes, so they will most likely be pink. But do continue fertilizing with aluminum sulfate every year either in late fall or early spring (if it's the blue or purple color you desire).

Because Rhapsody Blue blooms on both old and new wood, it's fussy about pruning time, granting you just a narrow window of opportunity. On the one hand, you won't want to prune too early, otherwise, you'll lose the first flush of flowers (those that bloomed on the old wood). On the other hand, if you wait too long, it may be too late for the buds to set on the new wood (the buds that you'll be counting on for next summer's first flush of flowers). In this sense, it poses a pruning challenge similar to that of a clematis vine such as Dr. Ruppel clematis. The sepal color fades somewhat by early August, so that's the best time to prune from an aesthetic standpoint.

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