At least half of the basic land cards in your library are Forests.
You have a land card in hand.
Steps
1Play a land.
2When the land enters, Springheart Nantuko triggers, causing you to pay to create a token copy of Avatar of Growth.
3When the Avatar of Growth token enters, it triggers, causing each player to search their library for up to two basic land cards and put them onto the battefield. Search for a Forest and any other basic land.
4When the basic lands enter, Springheart Nantuko triggers twice.
5Holding priority, activate two lands by tapping them, adding .
6Resolve the first Springheart Nantuko trigger, choosing not to pay and creating a 1/1 Insect creature token.
7Resolve the second Springheart Nantuko trigger, causing you to pay to create a token copy of Avatar of Growth
8Repeat from step 3 until your library contains no basic lands.