Very Very Big Terrain, how to show it?

Hello, everybody, i have a very very big terrain which is 5x5 Square Kilometers to show, and i set the terrain's resolution, width & length all to 1025 to adapt to the real world's terrain.I read the DEM data form database and show it, the terrain is so big that my computer get blocked! How can i solve this problem? Using mesh? if so, i won't be able to plant trees and grass and other goodies of terrain.

Any reply will be appreciate!

I assume you can divide it into several smaller terrains?