Annual plant - Ichinenso

Japanese: 一年草 - いちねんそう

Flowering plants are classified as annuals, biennials, and perennials depending on the length of time it takes from sowing to germination, flowering, and fruiting. Plants that flower within one year of sowing and then die after producing seeds, or die due to cold or heat, are called annuals. Generally, these are ornamental plants grown in gardens, but the same is true for flowers grown in the mountains and fields. The time it takes from sowing to fruiting depends on temperature and sunlight, and in Japan they are treated as annuals, but in tropical areas with sufficient temperature and sunlight, some become perennials. They are classified as spring-sown or fall-sown depending on the optimum temperature for seed germination and their heat and cold resistance during growth. Plants that are sown in autumn and flower the following spring are sometimes called biennials, but in flowering plants, they are often collectively referred to as one- and two-year-olds.

[Yasuo Hori]

Spring sowing

Many species have an optimum temperature for seed germination above 20°C, and grow well under high temperatures and long days. Therefore, if spring seeds are sown from summer to autumn, the short day conditions will occur soon, and some species (morning glory, autumn-flowering cosmos) will produce flower buds before they have fully grown. Spring seeds include sunflowers, impatiens, portulaca, zinnia, and cockscomb.

[Yasuo Hori]

Autumn sowing

The optimum temperature for seed germination is around 20°C, and these flowers prefer cooler growing conditions. Therefore, most of them flower from winter to spring. Examples include snapdragons, marigolds, sweet peas, and corn poppies.

[Yasuo Hori]

Main annuals (sown in spring)
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Main annuals (sown in spring)

Main annuals (sown in autumn)
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Main annuals (sown in autumn)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

草花は、播種(はしゅ)から発芽、開花、結実までの暦年の長さによって、一年草、二年草、多年草に分けられる。種子を播(ま)いてから1年以内に開花し、種子を結実して枯死するか、または寒さ、暑さのために枯死するものを一年草とよぶ。一般的には園芸上の観賞用草花をさすが、野山における草花も同様である。播種から結実までの長さは温度や日照によって左右され、日本では一年草の扱いをするが、温度や日照の十分な熱帯のような所では多年草となるものもある。種子の発芽適温や生育にあたっての耐暑性、耐寒性などによって、春播きと秋播きに区別される。なお、秋に播いて翌春開花するものを二年草とよぶこともあるが、草花類ではこれらを総称して、一、二年草として扱うことが多い。

［堀　保男］

春播き

種子の発芽温度が20℃以上を適温とするものが多く、高温、日長下でよく生育する。したがって春播き種子を夏から秋にかけて播くと、すぐ短日状態になるので十分成長しないうちに花芽をつけるものもある（アサガオ、秋咲きコスモス）。春播き種にはヒマワリ、ホウセンカ、マツバボタン、ヒャクニチソウ、ケイトウなどがある。

［堀　保男］