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.