C. goeringii basic colour (wild type) is green. Flower colour mutations occur and the Japanese has been collecting these types of C. goeringii for hundreds and hundreds of years (they have been over collected in Japan, so it is very rare to find a C. goeringii that has a coloured flower in Japan). In the wild, flower buds start to form by the end of July/early August and will only bloom in the followng Spring (March). For 9 months, the flower buds are covered by leaf litter, so the shading technique is used to simulate what happens in nature.
99% of Chinese C. goeringii are green, so no shading is required. For coloured varieites (red, purple, orange, yellow, white), shading is required. Since most coloured varieites are Japanese and Korean origin, this is what you do for Japanese and Korean C. goeringii. The reason to shade the bud is to make sure that the buds are developed in the dark without any chlorophyll, so it will produce vibrant colours when it blooms in the spring. Also, the covering softens the flower petals during flower development and it will produce better flower quality as well. To produce the vibrant colour in the spring, vernalization is also a very important factor (required to bloom and get the colour right). Vernalization starts around Winter Solstice and ends when the flowers bloom (min 50 days and for many varieites longer). I end vernalization when the flowers are ready (naturally), I don't abruptly stop vernalization as many growers do, by stop vernalization abruptly, the flower buds can go into a shock, hence, abort the flower buds. During vernalizaton, the temperature must be between 0C-10C at all times (no higher and no lower). It is the combination of shading the flower bud and the near-freezing temp during vernalization, that will give these vibrant flower colous in the spring.
Attached is a picture of C. goeringii "Haruka" (Japanese) 日本春蘭「春華」。This is another C. goeringii in my collection. There are 4 flowers in the picture, the 3 flowers that were shaded, produced white tall stem with vibrant orange colour (desired), with correct petal shape (lotus plum flower petal shape). The 4th flower, as an experiment, I didn't shade the bud at all, and the flower colour is muddy and dull with a short flower stem (not desired), and not so good flower petal shape. This plant produced 3 flower buds this year (bloomed 2 years in a row already with 4 flowers every year), but I decided to pluck all of them this year, so will give more vigoruous growths next year.
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