A rainy day today, and I am investigating color, namely blue. The effects of
temperature and weather on apple color is general knowledge here, and driving
through the orchards I began to wonder which external influences can be used to
heighten the blue color of orchids.

This abstract came up in The Journal of Horticultural Science and Biotechnology:

"This study aimed to understand factors affecting leaf pigmentation of the woody
subtropical plant Chrysobalanus icaco, referred to as cocoplum. The effects of
temperature, UV-light and magnesium treatments were examined at different
developmental stages. Shoot growth intensity and chlorophyll concentrations
increased while anthocyanin concentration decreased with rise in temperature.
UV-a light had a slight effect on shoot growth, but no effect on the pigment
concentration of the leaves. Anthocyanin concentration decreased while
chlorophyll increased as leaves matured. The change in anthocyanin concentration
was due to dilution of the pigment at the early stages of development and its
degradation later on. In an attempt to inhibit anthocyanin degradation in
maturing leaves, whole plants were treated with magnesium salts. Magnesium
increased anthocyanin concentration two fold at the developmental stage at which
degradation was detected in control plants. By controlling UV-a light via
shading, applying magnesium treatments, growers may manipulate both plant height
and colour, thereby increasing the horticultural value of the crops."

This from the Journal of Commodity Science:

M. Fiorini, G. Barbiroli, P.G. Pifferi, "Effect of pH and temperature changes on
the colour of anthocyanins"

Abstract

"Structural transformations of anthocyanins in water solution at different
temperature were observed by measuring objective colour parameters Lightness,
Chroma and Hue according to CIE specifications. The pigments selected for this
study were glycosides of the most common anthocyanidins: Pelargonidin, Cyanidin,
Delphinidin, Petunidin, Peonidin and Malvidin. When pH was increased stepwise
from acid to acidic and then basic values, structural transformations of
anthocyanin pigments resulted in a general increase of Lightness, while Chroma
and Hue showed more complex change patterns. Temperature had a little influence
on the final Lightness, Chroma and Hue values, but at the lower temperature, 10
and 25 °C, Hue values characteristic of blue region were observed for some
anthocyanins at pH values between 3 and 7. Finally, in the experiments where pH
was held at constant values close to 1 and pigment concentration was decreased
by dilution, Lightness, Chroma and Hue changes were completely different from
the previous experiment set. This clearly indicated that colour measurements
were able to distinguish colour changes due to structural transformations from
those changes due to simple dilution effects."

This from Hydrangea production:
For blue sepals:
ample supply of Al (greater than 100 ppm); drench blue plants during Sept. with
Al sulfate, 2 applications 14 days apart
medium N levels (20-30 ppm)
low P level (1-5 ppm)
high K (25-50 ppm)

So my question for you chemistry and orchid fanatics is, how many, if any of
these measures, and which others could be tried to enhance blue color in
orchids?

Measures in short:
-Magnesium
-Aluminum
-Low temps
-Light
-Fertilizer
-pH
-reduced watering

Thanks at least for reading if my thoughts are way off line.
--
Reka

This is LIFE! It's not a rehearsal. Don't miss it!
http://www.rolbox.it/hukari/index.html






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