This is from my blog. I hope it will answer your question.
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I have not really given it any serious thoughts until recently. But
frankly, how do you distinguish between poetry and prose? Take the
following piece for example,
When lives are at stake,
would you risk
not reporting it?
If you see anything
or anyone suspicious,
inform our staff
or call 999.
And dont leave
your belongings unattended.
We all have a part to play
in keeping Singapore
Safe.
Do you consider it a poem? It is actually a copy of the notice put
up at various MRT stations to remind commuters to stay alert. I
chopped it up and arranged it to look like a poem. Okay, okay, this
is not really a good example.
But what about this?
And then comes Spring.
The sun is bright,
the water sparkles,
and the lobsters are active again,
swimming about, eating
like kings, and vying
for a place in your
Butter-browned top-sliced
frankfurter bun.
Would you categorize it as poetry? Better than the previous one
right? In fact it is a passage taken from one of the articles in
It mustve been something I
ate by Jeffrey Steingarten. Again, Ive chopped it up and
try to pass it off as a poem. 
Basically, there are two things I look out for in a piece of
writing before I decide whether it is a poetry or prose. Firstly is
the existence of poetic devices such as meter, rhyme, imagery,
metaphor, compression, etc. Secondly is its overall effect on me. I
need to be delighted, to be surprised, and if you could stun me
with it, the better; I will not hesitate to give you an A Plus.
To quote Emily Dicknson,
If I read a book [and] it makes my whole body so cold no
fire ever can warm me I know that is poetry. If I feel physically
as if the top of my head were taken off, I know that is poetry.
These are the only way[s] I know it. Is there any other
way?
To illustrate the second point, two poems immediately come into my
mind. Coincidentally both are very short poems. One is a haiku by
Taniguchi Buson -
The piercing chill I feel:
my dead wife's comb, in our bedroom,
under my heel . . .
And the other poem is Accident by Gilbert Koh, a
local poet I greatly respect.
He once told me,
A poem has to show me something that I wasn't aware of; or
it has to show me something that I was aware of, but in a way I'd
never thought of before. If I don't discover anything new in a
poem, then it doesn't work for me. It's not a poem to
me.
I have no problem with that. But what if instead of a poem, it is a
prose that show me something that I wasn't aware of; or it has to
show me something that I was aware of, but in a way I'd never
thought of before. If I don't discover anything new
can I still
consider it a poem? In fact many articles written by Mr Wang in his
blog "Did Mister Wang Say So?" meet the above requirements, but
they are definitely not poetry.
Maybe as suggested by Gilbert,
And if it is a good piece, does it really matter whether
it is more correctly classified as prose or poetry?
Well sorry Gilbert, but it does matters to me because I am the
stubborn type.
Although the boundary between poetry and prose remind obscure but
there is still hope; as Joan Houlihan in her reply to Fred
Moramarco said
While I agree that it is basically impossible to
successfully and fully define a poem, I maintain that it is
possible to define a non-poem by its lack of poetic
conventions.
In my opinion, if you write a prose using poetic devices, if you
insist, you can call it a prose poem. On the other hand, if you
write a poem in the manners as if you are writing a prose, it will
remain a prose, nothing but a prose.
