So I just had a look at the haiku wikipage, I thought I remembered that haiku wasn't this easy, and lo and behold there were more 'rules'. Not sure I will adhere to them, but maybe someone else is interested.
Short version:
Haiku is a very short form of Japanese poetry in three phrases, typically characterized by three qualities:
1. The essence of haiku is "cutting" (kiru).
This is often represented by the juxtaposition of two images or ideas and a kireji ("cutting word") between them, a kind of verbal punctuation mark which signals the moment of separation and colours the manner in which the juxtaposed elements are related.
2. Traditional haiku often consist of 17 on (also known as morae though often loosely translated as "syllables"), in three phrases of 5, 7, and 5 on, respectively.[3]
3. A kigo (seasonal reference), usually drawn from a saijiki, an extensive but defined list of such terms.
Long version:
https://en.wikipedia.org/wiki/Haiku
Guess I'm gonna read some examples and try again... :)