![multiple colors in rose diagram multiple colors in rose diagram](https://help.rockware.com/rockworks17/WebHelp/rose_freq_sm2.png)
But at neutral to basic pH, aluminum precipitates as aluminum hydroxide, making it unavailable for incorporation into the shrub. These aluminum ions can travel from soil into the plant. In acidic soils, aluminum occurs in what are called coordination complexes, with Al 3+ ions at the center, surrounded by bonded strings of other molecules. The chemistry of aluminum in soil establishes its different properties under acidic and basic conditions. Growers of hydrangeas with blue blooms must regularly water with aluminum sulfate drenches onto the potted medium to maintain the needed levels to force the desired blue coloration (but they cannot water too often or the excess Al 3+ will kill the plant). However, such imposed red-to-blue or blue-to-red color changes do not happen instantaneously it often takes one or two growing seasons to instill the desired color on shrubs within one’s flower gardens. Conversely, if one wishes to change blue-blooming hydrangea to red-blooming, adding lime (calcium hydroxide, Ca(OH) 2) results in basic soil and the desired color transition. The best soil additive for bluing is one that contributes both, such as commercially available aluminum sulfate, Al 2(SO 4) 3. Consequently, for the bluing of hydrangea blooms, one needs both aluminum ions and acidic soil. But in neutral to basic soil, the ions combine with hydroxide ions (OH -) to form immobile aluminum hydroxide, Al(OH) 3. Aluminum ions are mobile in acidic soil because of the ready availability of other ions they can react with, which can be taken up into the hydrangea to the bloom where they interact with the normally red pigment. The role of aluminum has been known since the 1940s, but it did not reach the mainstream horticultural literature until about the past two decades, and the exact mechanism was only recently defined. Hydrangea colors ultimately depend on the availability of aluminum ions (Al 3+) within the soil. The answer goes even deeper into the connection between soil composition and sepal color- a connection that has inspired our ongoing research into the biochemistry of these flowering plants. Soil acidity actually is not the underlying chemical mechanism behind the color change. Hydrangea colors turn out to be even more complicated that that, however. All these strategies tend to turn soil more acidic, and eventually transform the bloom color to blue. Homespun recipes abound for changing the pink blooms of a hydrangea to blue: pouring vinegar or lemon juice on the soil mulching the plant with coffee grounds, citrus fruit rinds, or pine tree needles or burying rusty nails, old tin cans, or copper pennies next to the bush. In fact, a hydrangea can have different bloom colors on the same bush if the roots of the plant sample soils of differing pH. The hydrangea is unique among plants in this ability to indicate soil acidity.īecause of this trait, gardeners can chemically manipulate hydrangea bloom colors using soil additives. The hydrangea’s bloom color reveals the pH of the soil, but with its distinguishing colors being the reverse of those for litmus paper. Such blooms have blue sepals when the shrub grows in acidic soil, but develop red or pink sepals when grown in neutral to basic soils. In a similar fashion, the color of many hydrangea blooms acts as a natural pH indicator for the soil in which the plant grows. When one dips blue litmus paper into an acidic solution (pH 7).
![multiple colors in rose diagram multiple colors in rose diagram](https://image.shutterstock.com/image-vector/vector-set-different-color-roses-260nw-581033536.jpg)
At the molecular level, acids are proton (or hydrogen ion) donators and bases are proton acceptors in chemical reactions. They are more akin to the colors seen in litmus paper, the chemically treated strips classically used to determine whether solutions are acidic or basic. Hydrangea colors are not what they seem, either they are not the result of a variety of different pigments, as is the case for flowers such as roses or tulips. Noticeably absent from the kaleidoscope of possible hydrangea colors are yellows and oranges.
![multiple colors in rose diagram multiple colors in rose diagram](https://mindbodygreen-res.cloudinary.com/images/w_767,q_auto:eco,f_auto,fl_lossy/org/nm3kmf4hykgwu4g29/pee-color-chart.png)
Color intensities run the gamut from vibrant to pastel. The bloom colors are what really make the hydrangea stand out: They range from pink to blue, including all shades of lavender to violet to purple, as well as green and white. For starters, the bloom of the hydrangea is not a true flower, but an inflorescence: Sepals, or modified leaves, make up most of the bloom and overshadow the small, almost unnoticeable fertile floral portions at the center.