Traditionally haiku contains three lines and 5-7-5 syllables. You can write a little shorter or longer, but try to keep the three lines and around seventeen syllables.
Important is that the poem reflects the haiku spirit. Two lines express something concrete happening – a scene and action, and the third contains a surprise, a contrast or a reversal – a change.
One opinion holds that 12 syllables would better correspond to the Japanese
language style. Especially Swedish and English are different from Japanese or Finnish structure and in Sweden shorter lines are used.
A seasonal word is often used in haiku poetry, like snow, crocus or apples. Nature is very much present in the poems.