looks like a general texture creation technique from a photo.

At a glance, looks like you get a texture. Resize your image canvas size and anchor it to the left. Duplicate it on a new layer, flip it using the transform tool so it's mirrored, then flattern, and use the clone stamp and healing brush tools to remove the mirroring and keep the resolution.

I would think you would then use Filter > Other > Offset to work on the edges in the same fashion so it can tile without seams, and any other distinct bits that will show up when tiled. Probably use colour balance and Hue/Saturation to equallize the various hues so you dont see any tell-tale repeitions when you tille it loads of time. You can also create a new layer, fil with a green and use blending on the layers to help too, plus some use of the sharpen too.