Here's how I learnt it from my father:

Spring is sprung,
The grass is riz,
I wonder where the boidies is.
The boid is on the wing.
Why that's absoid,
I always hoid
The wing was on the boid.

Just a few days ago I was looking for this to see who wrote it (Ogden Nash is a popular choice, but I think he just gets lumped with all these, like Oscar Wilde and Mark Twain). I couldn't find any definite version or author, though there are lots of versions out there. But I did come across a great big list of hundreds and hundreds of pieces of poetry mentioning spring - mainly Dickinson, Whitman, Frost, but lots of others (including copyright violations - Plath, Hughes, Neruda, Dylan Thomas etc).
Funny thing is it's the result of a search for the same ditty:

http://www.americanpoems.com/search/spring_sprung_grass_riz