I live in zone 7 and planted white pampas grass in early september. Our winter was mild and now in mid-may there are a few green leaves shooting up but not many. When does Pampas Grass usually leaf out in Zone 7?
Summer Grasses are some of the last plants to start growing in the gardens.
These articles have more information.
You can also check with your County Extension Office to see if they have dates of bloom time for you Pampas in your region.