Do I need a sub with landscape speakers?

For a courtyard at background volume, satellites can be enough. For a real backyard or pool, a burial or hardscape sub keeps bass even at low volume.

Can I add a sub later?

Yes. AcoustiScape and UltraScape sats are built to pair with SubTerrain or hardscape 12-inch later.

When a burial sub belongs in the yard

Landscape satellites cover mid and high frequencies. Outdoors they lose weight first. UltraScape packages the sub with four satellites so the first cart is already balanced.