# They are planted

"Yahweh has planted them" or "Yahweh takes care of them as if they were trees he had planted" 

# in the house of Yahweh ... in the courts of our God

The psalmist speaks of people who truly worship God as if they were trees growing in Yahweh's house. 

# they flourish

"they are growing well" or "they are very strong" 

# in the courts of our God

in the courtyard of the temple in Jerusalem.