Flowers - Iris - Blue

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edit @ 2006/08/10 00:03:06

Source: http://www.usna.usda.gov/Gardens/faqs/hydrangeafaq2.html

How do I change the color of my hydrangea?

Flower color in H. macrophylla is dependent on cultivar and aluminum availability. Aluminum is necessary to produce the blue pigment for which bigleaf hydrangea is noted. Most garden soils have adequate aluminum, but the aluminum will not be available to the plant if the soil pH is high. For most bigleaf hydrangea cultivars, blue flowers will be produced in acidic soil (pH 5.5 and lower), whereas neutral to alkaline soils (pH 6.5 and higher) will usually produce pink flowers. Between pH 5.5 and pH 6.5, the flowers will be purple (see image at left) or a mixture of blue and pink flowers will be found on the same plant.

It isnt unusual to find inflorescences that arepart pink and part blue (see image above).





There are a few cultivars that never produce blue flowers. In low pH soils, flowers of these "non-bluing" cultivars turn a dull reddish-purple. In higher pH soils, the flowers of these cultivars are a vivid deep pink color. Some non-bluing cultivars are 'Alpengluhen' (see image at above),

'Pia' (see image above),




and 'Kardinal' (see image above).

To change the color of a hydrangea planted in the garden, it is necessary to change the soil pH. To raise the pH, add lime. One way of lowering the pH of the soil is to add aluminum sulfate. Additions of acidic organic matter (peat, pine bark) can also help lower soil pH. Exact amounts of lime or aluminum sulfate necessary to get the desired flower color will vary depending on current soil pH and soil type.