Both karl and Antoni Wyszynski are incorrect; the Nemata, Grove Guardian/Earthcraft/Wild Growth combo sent in by Kip Will DOES work. They are correct that you can not tap a creature to activate it's own ability unless you have controlled it continuously since the beginning of your most recent turn.  However in this example you do not tap the newly created saproling tokens to activate their own ability, but to pay the cost of an activated ability of another permanent.  The saproling tokens in this example do not need Haste in order for this combo to work.