Text (UL+errata): 3/3. ; When ~this~ enters the battlefield, all green creatures get -1/-1 until end of turn. [Oracle 2009/07/08]
The -1/-1 penalty is given to all green creatures in play when the triggered ability resolves. It's a one shot effect and will not apply to green creatures that enter play later in the turn. [Urza's Legacy FAQ 1999/02/03]
