It should be possible to get rid of newly (or not) planted crops much like it is for trees - not just by harvesting them when they are grown-up.
Once upon a time you could destroy them by building a Trellis on top of the tile: viewtopic.php?f=42&t=49456 - but I guess this was a glitch and not intended.
But it should be possible to just pluck the sprouts, or destroy them like other objects, even when newly planted.