Get Michael O'Donnell's book "Turning Green Wood". It will give you all
the answers. It's a great book. To keep green wood from splitting you
can't let it dry out until you are done. You must keep it damp and you
must turn the walls thin and to a consistent thickness. Thin at top and
thick at bottom will guarantee splitting. Spray it with water if have
to to keep it moist while turning. Also, if you use fruit woods, they
are much more likely to split. This is not to say that the bowl won't
warp...it will but that is often the charm of turning green wood.

If you don't want splitting or warping, search out past threads about
alcohol, liquid detergent and microwaving rough turned bowls.