Newb Question - turning a bunch of TriMesh into a single Object?

Hello, I'm new to jME and 3D programming in general.

I'm looking to make a cell based map setup which was originally going to be 2D, but figured I would give 3D a shot.  After running through the tutorials I decided to try my setup using flat TriMeshes as cells.  Each cell would be some simple texture, such as grass, dirt, rock, etc.

As a simple test I made a couple floor loops that laid out X by X number of TriMeshes and threw a grass texture on it, and the results where exactly what I was looking for.  However I take a huge hit to my FPS which I believe is because each TriMesh is a separate object.  So my, for instance, 30x30 TriMesh floor is 900 objects and 1800 Triangles.

I noticed the Maggie Model demo also has 1800 triangles, but my FPS stays around the 1.8K idle mark my PC seems to run jME at, but Maggie is only made up of three objects.

I assume my problem is I need to get my 900 TriMeshes into a single object.  Is there something simple I can add them to, such as a node (this didn't work as you probably all know) where jME will treat them as a single object?

Also, another thing I noticed, with the 900 TriMesh, I can see grid lines…  Is there any material setup, or effect I can use to make these lines go away/less noticeable?

Thank you for your time, and thank you jME Devs for all of your hard work.

Edit:  In case anyone is wondering why I would want this cell/tile setup in a 3D game, it is because I want it to be a game with a dynamic landscape that can be changed by players.  The information for the world will be stored in a server database and fed to the client to render.

Edit2: I also have another question I may as well ask here.  If I store the TriMesh's in a 2D array, can I reference them after they have already been added to the rootNode and displayed on the screen?  For instance, say if a specific cell changes texture, can I reference it such as mapCells[100][25].setRenderState(TextureState) ?

look at the terrain classes, they are exactly what you need. (a grid terrain, but only one single object)

Will do, thank you very much.

Also new here. Out of curiosity, can someone describe why he was getting the slowdown, and if it was because they were separate objects, how one would go about joining them?