I baked three 6 inch square cakes today. I filled and stacked all three. The height is just a little over 5 or so. I plan to cover this in fondant but wasnt sure if I should have put a cake board in there for support. It's a Tiffany box smash cake so I wanted it to look like the box so I wanted it to have a Loire more height than just the 4 inches. I need to cover it tomorrow with fondant, but before I do wanted to make sure that the cake wouldn't buckle from its height and no board. Please if anyone can tell me if it will be okay or if I should try to trim some off the top before I start to ice and cover it. Thanks!!!

It should be fine.

If your traveling with the cake I would recommend putting a dowel through the middle. I wouldn't take any chances.

You don't need a board, but I agree that you need a dowel through the center if you're traveling. I had done several three-layer cakes, but recently had one slide and lean when I hit a pothole.

A single dowel thru a cake without a board in it won't do any good. It's like spiking air. A good sideways jolt and the cake will just tear off of the dowel. If that spike goes thru a board, the cake can rotate around it, but won't tear.

When I have a large, multi-tier cake with boards & supports, I insert 2 full length spikes if it's going to travel. With 2 spikes, the cake can't go anywhere and certainly can't rotate.

A 6x6 cake should be fine without a board between any of the layers.
I don't think you'd want a board in there, anyway, because it's a smash cake. If you placed a board between the layer's, you'd have to put dowels/straws in the bottom, and you don't want people smashing a cake with dowels in it.

Rae