How Does Light Affect Orchid Growth? A Detailed Guide to Orchid Light Requirements
Light is the energy source for orchids to produce nutrients, and it is also a necessary condition for chlorophyll formation. In orchids, from the formation of chloroplasts, the opening and closing of stomata, the absorption of nutrients and water, the proliferation of cytoplasm, the formation of flower buds, and the production of organic matter, as well as nectar secretion, fragrance release, and other basic physiological life activities, every aspect is affected by light.
When the temperature is 20-25°C and exposed to direct sunlight, the photochemical reaction between chlorophyll in orchid leaves and light is very rapid. Above 30°C, the chlorophyll in the grass-like leaves automatically decreases, the leaf color fades, and a gray visible film gradually forms to reflect sunlight and prevent sunburn. This condition can only be maintained for a relatively short time; if it lasts too long, it starts from the tips of the orchid leaves and the whole plant gradually withers and dies, especially older plants, which first turn yellow and then scorch. Below 20°C, orchid leaves can also automatically regulate the amount of chlorophyll, increasing chlorophyll to absorb more sunlight, so as to absorb more carbon dioxide and ensure the nutrients needed for orchid growth. This ability was formed over many years of orchids growing under trees, in forests, and among grasses. Therefore, orchids not only like sunlight but are also shade-tolerant. The fine leaves of orchids can, under shaded conditions, tolerate high temperatures of 45°C for a short time, but if this lasts too long the leaves will scorch. When there is sunlight, they can also tolerate a low temperature of minus 5°C for a short period, but humidity is an important condition.
Orchids are shade-tolerant and can grow at low temperatures, but in winter they need full sun. In cultivation and management, shading measures are mostly adopted in summer; orchid pots can be placed outside in sunlight to receive light, and above 30°C they can also be kept indoors. Although indoor scattered light is weak, it is still enough to grow orchids well. For orchids on a south-facing balcony, from after 9 a.m. to before 5 p.m. in summer, under well-ventilated conditions, bamboo blinds or commercially available black shade nets of 70% or more can be used for shading, and the same applies to various types of sheds. When shading, the blinds or nets should not be placed directly on the orchid plants, so as to avoid burning the orchid plants from the heated blinds or nets. It is best if the shading material allows some light to pass through; about 30% light is beneficial to orchid plants. Light can not only raise temperature but also prevent the breeding of fungi, bacteria, and viruses. Leaving gaps in the blinds or nets is helpful for ultraviolet rays to kill pathogens and viruses.
Light has a great influence on orchid reproduction. If there is no sunlight for a long time in winter and the temperature is relatively low, winter buds will not be produced, and if no new growths emerge in spring, the annual increase rate of plants will be affected.
(1) Different orchid varieties have different requirements for light conditions. For example, Cymbidium goeringii (Spring Orchid) and Cymbidium faberi (Huilan) need strong light, while Cymbidium ensifolium (Jianlan), Cymbidium sinense (Molan), and Cymbidium kanran (Hanlan) need weaker light. For the same orchid variety, light requirements also differ in different seasons and at different growth stages. For example, in summer and autumn they require morning light, diffused light, and weak light, and direct sunlight should be avoided to prevent sunburn; moreover, if the temperature is too high, orchid plants will enter diapause, there will not be much photosynthetic product, and without enough nutrients, the number of "flower primordia" will be small and flower buds cannot form. Conversely, if the shade is too dense and there is too little scattered light, the intensity of photosynthesis will be low, which also cannot meet the needs for the formation and development of "flower primordia," and flowering will be affected either way. In late autumn, relatively strong light can be given for 6-8 hours to promote flower bud differentiation and enrich the plant's own growth nutrients. In winter, when brought indoors, they must be placed in a location with relatively strong light.
(2) If orchids are kept in full shade, the leaves will be long, dark green, and thin, with sparse flowers, and the flowers will have no fragrance when they bloom; if the light is strong, the leaves will be short, withered yellow, and aged, and both the arrow leaves and flower buds may be scorched. With suitable light, the leaves are short and the flowers are numerous, with broad leaves and emerald color.
(3) When the flower buds break through the bracts, the sepals show color, and the petals open and spread, direct sunlight must be avoided; otherwise the petals are easily scorched or turn yellowish, and the flowers shrink and do not spread fully. If there is no light or insufficient light before flowering, the flower color will not be pretty.
(4) Orchids like scattered light and fear direct strong light. Scattered light provides sufficient energy for photosynthesis, allowing organic matter to accumulate and facilitating the formation of "flower primordia."
(5) Around the orchid nursery, relatively tall shade tree species should be planted, using their dense foliage and branches to shade the orchids, and when orchids need a relatively large amount of light, that is precisely the time when these trees gradually lose their branches and leaves. The orchid shed should be built as a shade structure that can be freely adjusted and opened in the morning and evening, so as to regulate the light transmittance needed for orchid growth and create a site with morning light in the morning, scattered light at noon, avoidance of western sun in the afternoon, weak light in the evening, exposure to rain and dew at night, and at least 2-4 hours of suitable light each day, with light transmittance reaching 40%. In such a place, the germination rate, flowering rate, leaf growth, and leaf color of orchids will all be in a relatively ideal state.