...But only God can make a tree.

Most people know that blowing your nose is, to the Japanese, a disgusting practice. It is ironic, therefore, that they find admirable another activity which is very similar, in that it requires no skill, takes very little time and produces nothing of any value. This is the composition of haiku ; the word originally meant heavenly wind-breaking, but nowadays refers to
"a form of Japanese poetry, consisting of 17 morae, in three metrical phrases of 5, 7 and 5 morae respectively[1]. Haiku typically contain a kigo, or seasonal reference, and a kireji or verbal caesura. In Japanese, haiku are traditionally printed in a single vertical line, while haiku in English usually appear in three lines, to parallel the three metrical phrases of Japanese haiku".

[To understand this fully you really need to follow the links to morae and kireji, though this may not help you much.]

Quite clear so far?

The rules are often interpreted loosely when writing haiku in English, and the usual result is a piece of staggering banality, for example:
When it is snowing
It is good to stay indoors:
Writing stuff like this

...or,

Today is the day
For Grumio to have fun
Let us wish him well