Environmental factors of orchids: light

Light, temperature and humidity are the three major factors for orchid growth. Its effect on the growth and development of orchids is very important. Most orchids are born in sunny and shaded natural environments, such as isolated trees, forest edges, light transmission in the forest, astigmatism on the rock wall, and so on. But different orchids have different requirements for light time and intensity. Like other plants, orchids can be divided into long-day orchids and short-day orchids. The long-day orchid blossoms with the lengthening of the day and the shortening of the night, while the short-day orchid blossoms with the shortening of the day and the lengthening of the night. The former mainly blossoms in late spring and summer, while the latter blossoms in late autumn and winter. There is also a third type of intermediate orchids between long and short days. This kind of orchid has the physiological preparation to blossom at any time, has more adaptability to the changing environment, and the flowering period is usually not strictly limited to a specific time. Usually short-day orchids can blossom under 8-hour sunshine, while orchids with long-day sunshine need 12-14 hours of sunshine to blossom. In addition to the length of sunlight, the intensity of sunlight also affects it. People often adjust the light time and the amount of light to advance or delay the flowering time. Of course, this is a very complex issue, and it also involves the mutual influence of temperature, humidity and other factors. It is necessary to have an in-depth understanding of the ecological environment of the origin of orchids in order to better combine the specific conditions for manual regulation.

The light requirement of orchids also varies from species to species. Even the same species is different in different growth periods and seasons. However, from the total light demand, it can be roughly divided into positive. Semi-negative and negative. Positive basically need no or only a little shading; semi-negative need shading 50%-70%; and negative need shading-70%-90%. This is only a general distinction, there is no absolute boundary. All kinds can be subdivided again. Generally speaking, deciduous species in dry season or winter need more light than evergreen species, epiphytic species are more than terrestrial species, leaflet species are more than large-leaf species, and thick-leaf species are more than thin-leaf species. This is a general conclusion drawn from a large number of analysis of the ecological environment of the origin of orchids. But this is not absolute, even if the same species are different in different regions and at different elevations.

Take domestic orchids as an example, Spiranthes sinensis and some Epipactis are positive and basically need no shading; Thunia alba, Arundina graminfolia and some Cypripedium need only 30% to 40% shading; some species of Vanda, Den-drobium and Oberonia need 50% shading; some species of COelgy-ne need 60% shading. National orchids generally like shade, most species need 70% shade, while most species of Chlanthe need 85% shade. This is a rough estimate, but in fact, the demand for light is sometimes very different within the same genus. For example, Paphiapofilum

Insigne was semi-negative, while Paphiope-dilum villosum was negative, Dendrobium fimbriatum was semi-negative, and Dendrobium henryi was negative. In the familiar national orchid, the situation is also different. Jianlan prefers light, with a shade degree of about 60% 70%, while Chunlan has a greater shade degree, about 70% 80%, and ink orchid needs 85% shade. In addition, shading has something to do with season, hour and temperature. For example, more shade in summer and less shade in winter; more shade at noon, less shade in the morning and evening; more shade in high temperature, less shade in cool; more shade in low altitude, less shade in high altitude, and so on.

The regulation of light is very important to the growth and development of orchids. Usually people can judge whether the light intensity is appropriate by carefully observing the growth of orchids. For example, if the leaf color becomes light green, it means that the light is too strong, and if it is yellowish-white or even scorched and withered, it means that the light intensity has exceeded the degree that the plant can endure. On the contrary, if the leaf color is dark green or dark green, and no luster, it means that the light is too weak. On the other hand, it can also be judged from plant growth and flowering. If the light is insufficient, the plant growth is weak, there are many leaf buds and few flower buds, the number of flowers is small and the color is not bright; if the light is too strong, the leaf buds are few and the flower buds are many, and the growth is abnormal.

The adjustment of light mainly depends on shading, that is, reducing the light rather than blocking it completely. Because most orchids are born in the shade with scattered sunlight in nature, semi-negative and negative species account for more than 4% of all orchid species. Therefore, imitating the natural environment, shading with plants is one of the more ideal methods. Some orchid farms in the south use planting trees and vines as part of the shade, while in the north, it is a good way to plant all kinds of plants around the greenhouse for summer shade. However, plants can not move freely, so it is necessary to use other artificial shading devices at the same time. In recent years, the sunscreen is the most widely used, which is light and durable, and there are different shading density specifications to choose from. Others, such as bamboo curtain, Reed curtain, grass curtain, colored plastic board, etc., can also be selected according to the actual situation. (Chen Xinqi, Ji Zhanhe)