Spring has sprung...

The grass is ris
I wonder where the flowers zis.

That's one version. My Grandad's version is -
Spring is sprung
The grass is riz
I wonder where the boidies is.
They say the boid is on the wing
But that's absoid
The wing is on the boid.

Origin is unknown. Some attribute it to Ogden Nash and others say Spike Milligan and the Goons.