Sweet-Spruce, King of Spring

When Sweet-Spruce, King of Spring enters the battlefield, if you control 3 or more plants, add {g}{g} to your mana pool. If you don't, create two
0/1 green plant creature tokens with defender.
Whenever Sweet-Spruce attacks, add {1} to your
mana pool for each plant you control. This mana
doesn't empty from your mana pool as steps and
phases end until end of turn.