Electric lighting cultivation

A cultivation method that uses electric lighting to promote or suppress the growth of crops. Long-day plants, which flower when the day length is longer, will flower even in seasons when the day length is short if they are grown in an environment that satisfies temperature and other conditions, and artificial lighting is supplemented to create long-day conditions. Similarly, supplementing artificial lighting with short-day plants suppresses flowering. Applying this property to cultivation, such as using electric lighting in greenhouses to make crops flower outside of their natural flowering period, is called electric lighting cultivation. The opposite cultivation method to electric lighting, which makes short-day plants flower in seasons when the days are long, is called shade cultivation.

Currently, the most common application of electric light cultivation is to suppress the flowering of chrysanthemums. Chrysanthemums are short-day plants that naturally flower in the autumn. In order to delay this and produce chrysanthemums for cut use in the New Year or early spring, electric lights are turned on from the evenings during the short-day season, around late August, to prevent flower buds from forming. Alternatively, electric lights can be turned on for a few hours in the middle of the night to interrupt the dark period and create relatively long-day conditions, but this will not cause flowers to form. In this way, if the light is stopped about 60 days before the desired flowering date, the plant will naturally flower in a short-day state, and flower buds will form and bloom.

Electric lighting cultivation of chrysanthemums has been widespread since around 1955, and there are collective cultivations in Shizuoka, Aichi, Hyogo, Fukuoka, and Kagawa prefectures. In addition to chrysanthemums, it is also used to regulate the flowering of long-day plants such as asters, irises, and stocks, as well as short-day plants such as dahlias and gladioli, but on a small scale.

[Hoshikawa Kiyochika]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

電灯照明を利用して作物の生育を促成または抑制する栽培法。日長が長くなると花をつける長日植物は、日長が短い季節でも温度その他の条件を満たした環境で育てたうえに、人工照明を補って長日条件にすると花をつける。また短日植物に対して人工照明を補うと花がつくのが抑制される。この性質を栽培に応用し、ハウス栽培などで電灯照明により作物の自然開花期以外の時期に開花させることを電照栽培という。なお短日植物を長日の季節に咲かせるための、電照栽培と反対の栽培法を遮光（シェード）栽培という。

　現在もっとも電照栽培が実用化されているのはキクの開花抑制である。キクは短日植物で、秋が自然開花期である。これを遅らせて正月、早春の切り花用に生産するために、短日の季節、8月下旬ころになったら夕方から電灯照明し、花芽着生を防ぐ。あるいは夜中に数時間電照して暗期を中断し、相対的に長日条件にしても着花しない。こうして目的の開花日の約60日前に電照をやめると、すでに自然は短日になっているので、花芽がつき、開花する。

　キクの電照栽培は1955年（昭和30）ころから広く普及し、静岡、愛知、兵庫、福岡、香川の諸県に集団栽培がある。キクのほかには、アスター、ハナショウブ、ストックなどの長日植物や、ダリア、グラジオラスなど短日植物の開花調節に用いられているが、規模はわずかである。

［星川清親］

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